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SCIENCE DEPARTMENT
- 2013 -
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This booklet has been created by members of the Science Department at
Canons High School. The aim of this booklet is to try and assist students
studying Triple Science with some of the trickier parts of the B3, C3 and P3
parts of the course and, in particular, it aims to tackle some of the generally
held misconceptions.
It also aims to tackle some literacy and numeracy issues in the three
disciplines.
We felt that it was important that this booklet did not turn into just
another text book or revision guide and should be seen as
something to compliment your existing texts whilst asking questions
that you would normally be asked in a lesson by a teacher.
In a very short time members of the department have compiled what we feel is
a very useful document that will hopefully lead you on the path to success with
Triple Science.
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Contents
The Human Respiratory System 4 Blood 6
Blood Vessels 8 Angioplasty & Stents 9
Biofuel 11 Biogas 13
Energy Changes in Chemical Reactions 15 X-Rays and Ultrasound 26
The Eye 28 Lenses 29
Fibre Optics 33 Hydraulics 34
Motors 35 Transformers 37
Circular Motion 39 Numeracy 40 Breathing 44
Glossary 46
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BODY
LUNGS
Vena Cava
Pulmonary
Artery
Aorta Pulmonary
Vein
Right Atrium
Right Ventricle
Left Atrium
Left Ventricle
Valve
Figure 1.
A diagram detailing the double
circulatory system of the heart and
the path of oxygenated and
deoxygenated blood around the
body.
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The heart is made of muscle and acts as a pump to move blood around the body. It is described as a double circulatory system because one half pumps deoxygenated blood to the lungs and the other pumps oxygenated blood to the rest of the body.
There are four chambers, the left and right atria and the left and right ventricles. You describe the sides of the heart as if it is inside you. Therefore when you look at it in a diagram, the right side of the heart is shown to be on the left and the left side is shown to be on the right.
Each chamber of the heart has a great vessel.
The vena cava brings deoxygenated blood from the body into the right atrium
The pulmonary artery sends blood from the right ventricle to the lungs
The pulmonary vein brings oxygenated blood from the lungs to the left atrium
and the aorta takes oxygenated blood from the left ventricle to the rest of the body.
This is the route blood takes around the heart:
Q. Why is the left side of the heart more muscular than the right side of the heart?
Q. What is the importance of valves in between the atria and the ventricles and in the aorta and pulmonary artery?
Q. Which side of the heart only has oxygenated blood and which has only deoxygenated blood?
Q. Why is the aorta the biggest blood vessel in the body?
Deoxygenated blood
from the body drains
into the right atrium via
the vena cava.
The right atrium
contracts to pump
blood into the right
ventricle.
The right ventricle
contracts to pump
blood out through the
pulmonary artery to
the lungs.
The now oxygenated
blood returns via the
pulmonary vein to the
left atrium.
The left atrium
contracts pumping
blood into the left
ventricle.
The left ventricle
contracts sending
blood out of the heart
to the body via the
aorta
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The blood is a very important tissue. It’s almost like the courier of our body: it delivers chemical messages (hormones), transports materials between different organs and tissues (such as urea), as well as important things our cells need to live.
Q. What other substances are transported in the blood?
In some countries, blood donations are in very short supply. Therefore scientists are trying to make artificial blood. In South Africa they have already made haemoglobin-based oxygen carriers which binds haemoglobin to a synthetic polymer but it doesn’t last long in the blood. Another type uses polyflourocarbons which are entirely synthetic. They are smaller than red blood cells so the patient needs to be supplied with more oxygen than normal in order to work. They can supply oxygen to areas which red blood cells would not usually be able to reach like swollen brain tissue.
Q. What are the risks of blood transfusion?
Q. Why do you think the use of artificial blood is so prevalent in Africa?
There are 4 main components of blood: red blood cells, white blood cells, platelets and the yellow liquid called plasma which they all float around in.
Red blood cells are responsible for transporting oxygen and carbon dioxide around the body. They are highly specialised in order to do this job effectively. It contains a red pigment called haemoglobin which the oxygen binds too to form oxyhaemoglobin which is bright red in colour. Red blood cells are also biconcave (they have two dimples in either side of the cell) and do not contain a nucleus.
Q. Why is blood red?
Q. Why do veins appear to be darker in colour compared to arteries?
Q. Why is not having a nucleus and being biconcave an advantage?
Q. Can you think of any disadvantages of a red blood cell not having a nucleus?
White blood cells are the army of the body. They are responsible for destroying any pathogen that may enter the body and cause harm. It can either produce antibodies, antitoxins, or just engulf them.
Figure 3
A white blood cell.
Figure 2
A diagram of a red blood cell,
showing their biconcave structure.
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Platelets are not complete cells; they are small cell fragments with no nucleus. They are like
the plumbers; responsible for plugging any leaks in blood vessels. When you get cut, they
gather where the cut is and form a clot to stop blood loss. This is what a scab really is.
Q. Apart from preventing blood loss, why are platelets also important?
Q. In the early development of blood transfusions, when people were bleeding severely,
doctors thought it was a good idea to give the patient an immediate blood transfusion.
These patients did not survive very long and many died of internal bleeding. Can you explain
why?
Figure 4
Red Blood Cells and
Platelets.
Platelets are not whole
cells, they are fragments
of cells with no nucleus.
Image courtesy of S. Kaulitzki
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Arteries carry blood away from the heart. It
has many special features to pump blood
under high pressure. It has a thick wall
which contains elastic tissue and a small
lumen to keep blood under high pressure.
The thick wall also contains muscle to help
control blood flow to different organs.
Q. Why is it important to keep blood at a
high pressure in arteries?
Q. Why would you need to control blood
flow to different organs?
Veins carry blood back to the heart.
Unlike the arteries they do not need
to maintain high pressure. They
contain valves and have a much larger
lumen than arteries.
Q. Why do veins contain valves?
Q. Can you name a vein that carries
oxygenated blood?
Capillaries are the smallest blood vessels, so small that
only one red blood cell can fit through at a time. They
carry both oxygenated and deoxygenated blood. They are
specialised to aid the exchange of materials between body
cells and the blood. They have very thin walls which are
just one cell thick to help the exchange of materials.
Q. What materials are exchanged between the blood and
body cells?
Elastic tissue and muscle
Small lumen
Big lumen
Red
blood
cell
Valve
Body cell
Thin wall Red blood cell
Figure 5.
A table detailing the structural specialisms of the 3
types of blood vessels: arteries, veins and capillaries.
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A balloon with a metal mesh (stent) is manoeuvred into the blocked artery. The balloon is inflated to break up the fatty deposits inside the
artery. The balloon is then withdrawn, leaving the stent in place to hold the artery open. Angioplasty is very similar, the only difference is
that there is no stent left behind, the balloon is just inflated to break up the fatty deposits on the inside of the artery.
Red
blood
cell
Fat
Balloon
Stent
Figure 6.
A series of diagrams
showing the steps
involved in unblocking
an artery using a stent.
A balloon with a wire
mesh around it is
inflated and the mesh
stays in the artery to
physically hold it open.
This procedure is often
used in the arteries
that supply the heart
muscle (coronary
arteries) and is also
used in blood vessels in
the brain to prevent
strokes.
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Valves are an integral part of the heart. A defective valve can result in serious problems
for the sufferer. They can be replaced by either a mechanical valve or a valve from a
human or a suitable mammal. Mechanical valves can last a lifetime but they can cause
blood to clot and damage red blood cells. Therefore patients with a mechanical valve need
to take anticoagulant drugs which stop the blood from clotting.
Q. What other problems could taking anticoagulants cause?
Q. Which patients do you think would be best suited to a mechanical valve?
Artificial hearts are a short term solution for someone waiting for a heart transplant.
Recently there have been huge leaps in the development of the artificial heart including
the first UK patient to be sent home with an entirely artificial heart in 2011.
Q. Why do you think an artificial heart has not yet been used as an alternative to a heart
transplant?
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Describe how ethanol based fuels are produced:
The term biofuel means a fuel produced from living plant material as opposed to fossil fuels
that are made from dead plant and animal material.
The following carbohydrate-rich plants are anaerobically fermented by microorganisms and
converted into bio fuels:
Wheat
Maize
Sugar cane
Sugar beet
The process goes like this:
1. The starch in the crop is hydrolysed by carbohydrases (enzymes)
2. Yeast is added to ferment the glucose anaerobically
Glucose Carbon dioxide + Ethanol
3. Ethanol is distilled and purified
4. Purified ethanol can be used as fuel or added to petrol to make it go further.
Put this process into a flow diagram then find a diagram of a bioethanol production plant,
copy and annotate it.
Explain that research is increasing the range of plant types and plant waste that can be
used as a source of ethanol:
Straw and wood are alternatives to using food crops. (This is important coz using food to
make fuel pushes up the price of basic food – meaning more poor people starving and
malnourished) the problem is they are made of cellulose and that is more tricky to convert
into glucose.
Scientists at York and Portsmouth University are taking part in the UK’s bioenergy research
programme. They are looking at gribble worms, Limnoria quadripunctata, wood borers that
are a pest on our nice wooden structures in the sea. They contain enzymes that digest
cellulose into glucose. Now wouldn’t it be handy if we could extract those enzymes and use
them in our bioethanol production plants? We could get bioethanol without taking away
food crops!
Watch and read this:
www.bbsrc.ac.uk/news/industrial-biotechnology/2012/121128-f-meet-the-gribbles.aspx
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Interpret economic and environmental data about fuel production by fermentation and
the use of these fuels.
Gasohol is a mixture of petrol and ethanol. The graph below shows the effect that
introducing it in Brazil has made on emissions of some pollutants.
What are the environmental effects of this?
What about other pollutants?
Are biofuels really carbon-neutral?
Think about: The use and production of fertilizers.
The transportation of the crops.
Heating the fermenter to the optimum temperature.
What do you think the economic effects are?
Would we be able to use this level of gasohol in Britain?
Do we have the land to grow the crops?
What would the economic impact be on food prices?
What other information would you need in order to make a proper judgement?
0
10
20
30
40
50
60
petrol gasohol +ethanol
gasohol +ethanol
gasohol +ethanol
<1980 1986 1990 1995
Average emissions per car in Brasil over the 15 years after the
introduction of gasohol.
Carbon Monoxide
Hydrocarbons
Nitrogen Oxides
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LO: Explain what biogas is
It is methane gas that can be used for furnaces and cooking stoves. A much safer option than an open fire in the house for cooking (less smoke and inhalants). It can also be used as a fuel for farm machinery.
LO: describe how biogas can be produced from plant and animal waste by anaerobic fermentation.
It is produced by the anaerobic fermentation (without oxygen) of waste products that contain carbohydrates. Examples of suitable waste are plant waste, animal waste such as manure and sewage sludge ad kitchen waste.
Carbohydrate Methane + Carbon dioxide (Microorganisms)
Very small scale biogas production can be done with the following method:
1. Dig a trench about 10m long and 1m deep.
2. Place a heavy-duty plastic bag in the trench.
3. The bag has an inlet and outlet pipes and a valve to draw out the gas.
4. Fill the bag 2/3 full of water
5. Fill the rest with exhaust fumes from a car (to make anaerobic conditions).
6. Add a mixture of water and faeces through the inlet pipe.
7. It take 18kg of faeces per day to make enough gas for the farmer.
Now find a diagram to go with this, draw and annotate it.
LO: evaluate the use of small scale biogas generators in a rural setting
Have a look at these websites, they have some interesting comments and information that will assist you in evaluating biogas generators in rural settings:
www.instructables.com/answers/Simple-designs-for-DIY-home-biogas-generation/
www.small-farm-permaculture-and-sustainable-living.com/methane_generator.html
home.btconnect.com/engindia/biogas.htm
www.heifer.org/blog/tag/biogas/page/2
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LO: Describe how biogas can be generated from domestic waste
There are thousands of biogas plants generating methane gas in Europe, they take organic
household waste and solid industrial waste and generate methane gas and fertilizer to be
used on crops.
The organic waste is shredded and fed into a primary mixing tank, some gas is given of here
and collected and the rest of the waste is passed through a heat exchanger (to warm it and
speed up the process) and into a digester tank (it is mixed in here too). Biogas comes out of
the top of the digester and solid waste is piped out the bottom. The biogas is then used for
fuels and the solid waste is turned into fertilizer to be sold or given to farmers.
These websites give real life examples of commercial biogas plants:
www.stormfisher.com/whatwedo.htm
chemewithaconscience.blogspot.co.uk/2010_12_01_archive.html
LO: Explain how cooperation between farmers results in the supply of energy to small
towns in rural locations
Farmers will give their manure to the biogas plants in exchange for the fertilizer at the end
of the process, in this way they are providing a service to their community and providing
methane that can be used for heating, car fuel and generating electricity for their local
town.
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‘A chemical reaction takes place when the reactant particles collide in the correct orientation with sufficient energy.’ This statement describes the requirements for a chemical reaction or a successful collision to take place. This topic explores the nature of energy changes in chemical reactions and the calculations that your will need to perform in the exam. What you need to be thinking about?
What types of energy changes take place during chemical reactions?
Why do all reactions need energy to happen and where does this energy come from?
Where do chemicals store energy?
What is the relationship between temperature and energy? When a reaction takes place bonds in the reactants have to be broken before new chemical bonds can form to make the products. It is logical to think that breaking strong bonds would require energy but for some students the notion of energy being released when new bonds form is not easily grasped. What needs to be considered is that most atoms are not stable unless they are chemically bonded to other atoms. This is how atoms achieve what is known as a Noble gas arrangement of electrons. When two atoms bond they achieve a stable arrangement of electrons which results in energy being lost to the surroundings.
So how can a reaction be defined as endothermic or exothermic? The answer lies in understanding how much energy is needed to break bonds (an endothermic process) and how much energy is released when new bonds are formed (an exothermic process). By comparing the magnitude of the two energy values a reaction can be defined as exothermic or endothermic. ‘A reaction is exothermic if the energy released when new bonds are formed is greater than the energy needed to break bonds’. The explanation needs to be practised as students often only talk about energy being needed when bonds are broken and made.
How would you phrase, in terms of bond breaking and bond making, the explanation for an endothermic reaction?
How can you measure energy changes taking place in chemical reactions?
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Many of you may have felt the bottom of a test-tube containing hydrochloric acid and magnesium ribbon. While the magnesium fizzes the tube gets warmer. The reaction is exothermic.
But how much energy is produced? How might you go about quantifying the amount of energy produced in a chemical reaction?
What would happen if the concentration of hydrochloric acid was increased or magnesium powder was used instead of ribbon?
From an industrial view point why is it important in knowing the energy change that takes place in a chemical reaction?
Calorimetry is used to measure the energy changes that take place in most chemical reactions. At GCSE the energy change that takes place during combustion, neutralisation, solubility and displacement reactions are commonly used examples. Figure 1 shows the apparatus used to measure the heat energy change taking place. (a) (b)
Figure 1. Apparatus used to measure the heat energy changes in chemical reactions. (a) a polystyrene calorimeter for measuring energy changes in neutralisation, solubility and displacement reactions. (b) a calorimeter used to measuring the energy released on burning a liquid fuel.
Describe the measurements would you need to make to calculate the energy change of a reaction when using the two methods of calorimetry shown in Figure 1?
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Calculating energy changes in reactions The basis of all heat energy calculations is an understanding of the concept of specific heat capacity. The specific heat capacity is the energy, in Joules, required to raise the temperature of 1 g of a substance by 1 oC. For pure water this value is approximately 4.2 Joules (Figure 2) and can be expressed as 4.2 J g-1 oC-1.
Figure 2. Diagram to illustrate the specific heat capacity of water. The relationship between temperature and heat energy is given in the expression:
Q = mcT
Q = thermal energy in Joules m = mass in grams (of the liquid you measure the temperature of)
T = change in temperature In the combustion of a fuel, the heat is transferred to the water (Figure 1). A polystyrene cup can be used as a simple calorimeter for measuring the energy changing of neutralisation, solubility and displacement reactions (Figure 1). In this case, the density of the solution is assumed to be the same as that of water.
The two methods described only give an estimate of the energy change that would take place during the reaction. Can you suggest reasons why?
Why does it not matter that the calorimetric methods described in Figure 1 do not measure accurate changes in energy when comparing different chemical reactions or the burning of different fuels?
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Calculating the energy change per mole of substance. The requirement at GCSE is to calculate all energy changes in kJ per mole (kJ mol-1). (Figure 2) The ‘mol’ refers to the amount of reactant that was used in the reaction. The mole calculation used would depend on whether the mass or the volume and concentration of the reactant were known.
To measure the energy released during the combustion of a fuel you would need to know the mass of the fuel burned. The moles of fuel burned can then be calculated using the above equation. Finally, to calculate the kJ released per mole, the energy released is divided by the moles of fuel burned. Example question A student carried out an experiment to measure the energy released during the combustion of an alcohol with the molecular formula, C5H12O. In the experiment, 1.76 g of alcohol was burnt. The energy was used to heat 250 cm3 of water from 24.0 oC to 78.0 oC.
Calculate the energy released in joules (J).
Calculate the number of moles of alcohol burnt.
Calculate the energy released in kJ when 1 mole of the alcohol burns. Answer
Energy released = 250 4.2 54 = 56700 J
oles of alcohol burnt mass
.
. 2 moles
Energy released in kJ per 1 mole of alcohol
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k energy released
. k
energy released in k
moles
.
. 2 per mole of alcohol
What would you do if you could not measure the energy change directly by experiment?
Using bond energies is an alternative method for calculating the energy change of a reaction in which the substances all exist as molecules. Molecules consist of covalently bonded atoms. Each type of covalent bond requires a certain amount of energy to break it known as the bond energy. As it happens, this is the same amount of energy released when the same bond is made. Table 1 shows the average bond energy of bonds commonly found in molecules you may come across at GCSE. Table 1. Example bond energies.
Bond Average bond energy in kJ per mole
O=O 498
C-H 413
H-H 436
H-O 464
C=O 745
C-C 348
The bond energies stated are average values. Furthermore, the molecules must be in
gaseous state.
How would using average values affect the calculation of the energy change? Calculating energy changes using average bond energies. The skill with these types of question is knowing how many bonds of each type are present in your reactant and product molecules. Once this has been established the rest is arithmetic. Worked example Let’s consider the example of hydrogen and oxygen reacting to form water. 2H2 (g) + O2 (g) 2H2O (g)
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Displaying the bonds in the molecules will make the calculation easier. The exam board usually does this for you.
Bonds on the reactants side Bonds on the products side
2 H-H = 2 436 = 847 4 O-H = 4 464 = 1856
O=O = 498
Total = 1345 Total = 1856
The energy released when new bonds are formed is greater than the energy needed to break the bonds in the reactants. This tells you that the reaction is exothermic. The difference between the two totals gives the energy change. Energy change = 511 kJ
What would be the energy change if only 1 water molecule had been formed?
21
Energy level diagrams and activation energy. The opening statement defining a successful collision refers to the reactant particles have ‘sufficient energy’. This quantity of energy is called the activation energy. The quantity involved is reaction specific but without it the reaction will not proceed. An energy level diagram represents the activation energy in the form of a ‘hump’. Knowing if a reaction is exothermic or endothermic is important but more important is knowing if the reaction has a high activation. Figure 3 shows typical energy level diagrams for an exothermic and endothermic reaction.
Figure 3. Energy level diagrams. The exam question will ask how you can tell if the energy level diagram represents an exothermic or endothermic reaction. The answer is to do with the products having less or more energy than the reactants. For example, if the products have less energy than the reactants then energy must have been transferred to the surroundings. This would make the reaction exothermic. Conversely, if the products had more energy than the reactants then the reaction would be endothermic. Adding a catalyst lowers the activation energy. This can also be represented on an energy level diagram with a lower ‘hump’ marking the activation energy. A catalyst is a substance that is not chemically consumed in a reaction. The catalyst provides a different way (or an alternative route) for the reaction to take place which needs less starting energy. This is why adding a catalyst makes a reaction faster.
Why does knowing the activation energy an important consideration in the chemical industry?
What are the economic and environmental impacts of using catalysts?
What are biological catalysts?
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Energy changes and reversible reactions
What is the difference between a reversible change and a reversible reaction? A reversible reaction is one in which products are made and reactants are reformed continuously in a closed system. Eventually, the reaction will reach a dynamic equilibrium where the concentration of the reactants and products remain constant because the rate of reaction is the same in both directions. Knowing the energy change of the forward reaction of a reversible reaction is an important industrial consideration. An exothermic forward reaction means that the backward or reverse reaction is endothermic. Therefore, heating a reversible reaction to increase the rate of reaction could result in a lower yield if the forward reaction is exothermic.
Why does the yield of a reversible reaction decrease if the forward reaction is exothermic?
The rate of reaction and the yield are two important considerations industry. Often the conditions used are a compromise. What does this mean?
Calculations involving titrations Titration calculations at GCSE can appear daunting but are in general one of the easiest chemical calculations you will perform. If anything, performing the titration itself usually causes the greatest anguish. A titration is an accurate analytical technique for finding the amount of a substance or its concentration using a chemical reaction and a balanced equation. At GCSE, a titration involves carrying out a neutralisation reaction to determine the concentration of an acid or alkali. For example, if the concentration of an acid is to be determined by titration then you would need to start with a standard solution of the alkali of known concentration and the balanced equation.
What is meant by a ‘standard’ solution?
What is meant by the term ‘concentration’ of a solution? The practical method is relatively standardised at GCSE (Figure 4) and there are many demonstrations available to view online. Search for the term acid/alkali titration.
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Figure 4. The apparatus used to perform a titration. The calculation is what this section will focus on. Ideally, you would want to perform a structured calculation but at GCSE this is not necessary so a few short cuts can be employed. Note, that short cuts would not be permitted at A level but your teacher will go through the correct steps required. The following word equation generalises what happens in a neutralisation reaction.
xAcid + yAlkali salt + water The x and y represent the number of molecules (also known as by the term moles). Most of the time the neutralisation reactions used in GCSE exam equations have x and y both equal to . You may even find questions where you are told that ‘one mole of acid reacts with one mole of alkali’ instead of being provided with the balanced equation.
What is the ionic equation for the reaction between an acid and an alkali?
Acids and alkalis are referred to as being strong or weak and concentrated or diluted. These terms are often used incorrectly. Explain the difference between the terms ‘strong or weak’ and ‘dilute and concentrated’ when describing acids or alkalis.
1. The burette is rinsed with the solution it will contain and
then filled.
2. A known volume of the acid/alkali is pipetted into the
conical flask.
3. A few drops of a suitable indicator are added.
4. The initial volume in the burette is recorded.
5. The solution in burette is added to the conical flask drop
wise while continually swirling the flask.
6. The titration is completed when the end point colour of
the indicator is reached.
7. The final volume in the burette is recorded.
8. The titration is repeated until similar values are obtained
(usually within 0.20 cm3)
Why is universal indicator not a suitable indicator to use in
titrations?
Why would you not rinse the conical flask with the solution
you intend to put in it?
The solution in the burette forms a meniscus. The advice is
to measure the volume from the bottom of the meniscus.
What effect would reading the top of the meniscus have
on volume of solution used in the titration? Explain your
answer.
24
The short cut you need for the titration calculation is as follows:
volume of acid used concentration of acid
volume of alkali used concentration of alkali x
y
or
A A
x
y
The concentration term used in the equation has the unit, mol per dm3. You will also need to state the concentration in gram per dm3. The conversion between grams and moles is given by the formula,
moles Mr = grams Example question A solution of hydrochloric acid is left out in an open beaker. The concentration labelled on the beaker is no longer accurate. The concentration of the acid is determined by titration using a solution of sodium hydroxide. HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l) The acid in 25 cm3 of solution completely reacted with 14.5 cm3 of sodium hydroxide of concentration 0.10 moles per dm3. Calculate the concentration in grams per dm3 of the acid in the solution. Answer Using the above expression, x and y both equal 1. VA = 25 cm3, VB = 14.5 cm3 and CB = 0.10 moles per dm3 2 A
. .
2 A . .
A . .
. . mol per dm
To express the concentration in grams per dm3, the number of moles is converted to
grams using the equation: moles Mr = grams The Mr of HCl = 36.5.
Therefore, the concentration of the HCl solution: 0.06 36.5 = 2.1 g per dm3
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Key terms glossary Bond energy – the energy needed to break one mole of a covalent bond in a molecule in the gaseous state. Calorimeter – apparatus used to measure the energy change taking place in a chemical reaction. Concentration – moles per dm3, the number of moles of solute dissolved in 1 dm3 of solution. Endothermic – a process that involves the transfer of heat energy from the surroundings to the reaction (also known as the ‘system’). The temperature of the surroundings decreases. Exothermic – a process that involves the transfer of heat energy from the reaction to the surroundings. The temperature of the surroundings increases. Mole – this is the amount of any substance expressed in terms of the relative numbers of
particles present in a given mass. One mole of any substance contains 6.02 1023 number of particles which in terms of mass is the relative formula mass expressed in grams. For example, 1 mole of sodium is 23 g; 1 mole of magnesium oxide, MgO, is 40 g.
26
Most of you will have had at least one X-ray in your lifetime for a broken or fractured bone or to check the condition of your teeth and will therefore understand the link with medicine and dentistry.
Figure 1: X-Ray of a simple fracture Figure 1 shows a simple fracture of a bone, think about an X-ray you had taken, how was it done, was there any protective measures taken? Why? Why does the image only show the bone and not the other parts of the limb? There have been developments with X-ray technology in recent decades.
Figure 2: CAT scan Figure 2 shows a Computerised Tomography (CT) or CAT scan for the abdominal region of a patient, what are the obvious differences between these and the X-ray in Figure 1? You must be able to describe these differences.
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Another technology used by medics to view inside a person is ultrasound. Ultrasound describes the frequency of longitudinal waves above the upper limit of human hearing, i.e. 20,000 Hz (20 kHz).
Figure 3: Ultrasound scan
Figure 3 shows an image
of a foetus taken using
ultrasound. This image is
shown on a screen on a
computer, the transmitter
and receiver is placed on
the stomach of a pregnant
woman using a gel. How
are these images created
on the screen?
There are good reasons why an ultrasound is used for this type of imaging as opposed to using an X-
ray or CT scan, can you think what some of them maybe?
28
Your eyes are one of the most important pieces of apparatus that scientists like you use
which is why we emphasise you must protect them during practical investigations! Without
your eyes you would not be able to make as many observations.
Figure 4 Human eye
It is important that you can name the main features of the eye as well as being able to
understand how it works in creating images of objects from reflected light rays and how
some eyes need corrective lenses in order for them to view images clearly.
This topic will help you understand the foundations of Optics as a significant topic when
studying Physics in University. Optics is a branch of Physics relating to how light and other
forms of electromagnetic radiation interact with objects. You have experience of this
everyday of your life. What do you know from your own experiences?
Have you ever looked through a transparent pen or a liquid in a glass and noticed how the
world can get a bit distorted?
What is the significance of the cornea and lens being oval shaped? What does this do the
rays of light entering the eye? You should start to link this with the topic of refraction from
P1.
The Ciliary muscle has an important function in helping you focus objects that are far off in
the distance and objects close to your face. How?
29
If someone is unable to objects clearly they may need to go to an optometrist to get
corrective lenses. The simplest types of lens are converging (convex) and diverging
(concave).
Figure 5 Simple lenses – converging on top, diverging below
You need to understand how these lenses work in partnership with the lens in the eye to
focus images clearly onto the retina.
One of the biggest issues students have is drawing relevant ray diagrams for both types of
lens and describing the type of image that is formed.
You should recognise the following layout for the creation of an image using a converging
lens
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Figure 6 How an image is formed using a convex lens
In order to create this you start with the layout and draw an arrow from the top of the object to the
lens, parallel to the principle axis as shown below
Figure 7First stage of forming the image
Next, you draw the ray after it has been refracted by the lens through the focal point.
Image
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Figure 8 Next stage
Next you draw the an arrow from the top of the object through the centre of the lens until it touches
the first refracted arrow as shown below
Figure 9 where the rays meet
Finally, draw the image arrow between the principle axis and the point where the light rays meet
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Figure 10 Final formation of the image
You need to use the correct terms in order to describe the image formed. To do this you
need to compare it to the object, so in this case you would say that it is magnified (larger),
inverted (upside down) and real (you could project the image onto a screen).
The lens in your eye is a converging lens which means we see everything inverted!
It is important that you are able to do this procedure at different positions along the
principle axis. If the object is placed on the Focal point (F on the left hand side) it will not
produce an image as the rays will never meet! If the object is between the F and the lens
then the image will be formed on the same side as the object and will be the right way up.
Try it. This is how a magnifying glass works.
Figure 11 Lenses with different reactive indices
Figure 11 shows 2 different types of converging lenses. The lens on the left is made of a
material with a higher refractive index which means it can be thinner and give the same
effect as the thicker lens on the right.
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Many companies that provide broadband go to great lengths to highlight how fast their
broadband is compared to their competitors to try and get you to subscribe to their service.
One of the biggest breakthroughs in telecommunications has been the development of fibre
optic cables. If you see pictures of your street from years ago it will probably show
telephone poles with wires stretching to all the houses that had a landline. These days some
streets may still have the telephone poles (especially in ore rural areas) however most
communications are transferred via fibre optic cables because they can carry much more
data and the data can be digitised.
How is laser light sent down a fibre optic cable?
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Most cars have a mass roughly equivalent to a ton (1000kg) and you may have seen car
safety adverts on television showing how the damage to a person hit by a car depends on
the speed of the car. You will appreciate that a person hit by a car will do little damage to
the car, let alone make it stop so how is it possible that by pressing your foot on a pedal you
can make a 1 ton car stop?
Cranes are used to carry extremely heavy loads on building sites and yet all it takes is for a
machinist to push or pull a lever to raise these loads. There would be no way that the same
person could lift these loads so how is this possible?
The use of hydraulics based on the application of a seemingly simple equation.
Figure 12 How hydraulics work
As you can see on both sides the size of the pressure, P, is the same and actually all through
the yellow liquid the pressure has the same value – because it is a liquid and not a gas. The
size of the arrow representing the Force, F, is larger on the right because the area of this
piston is larger and so for the pressure to be the same, F must be larger. This means that for
a small force at the master cylinder (break pedal), a larger force is created at the slave
cylinder (brake) which is large enough to stop a car.
Have you seen in some dodgy soap-opera or silly film about furious fast cars, a car crashes
and someone gets hurt because someone cut the brake cable? What they are actually doing
is making the brake fluid leak out so when the person presses the break, the pressure is not
the same in the fluid between the cylinders, the brakes don’t work and the car doesn’t stop.
Aaarrrghhh!
Master Cylinder
P = F/A
Slave Cylinder
P = F/A
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Speaking of cars, well specifically electric cars, you need to understand how motors work.
People use motors everyday of your life from microwaves, electric fans, fans in electronic
devices to keep them cool, fridges, hairdryers, vacuum cleaners and the tube. Can you name
any more examples? How they work is quite simple and it ties in nicely with circular motion
but first we must think about what happens when current flows in a wire. The first thing you
might think of is that it may get hot due to resistance but it also has a magnetic field around
it.
Figure 13 Magnetic field around a current carrying wire
Hopefully you will appreciate the link between electricity and magnetism. You have already
studied the Electromagnetic spectrum which is part of a huge topic within Physics,
Electromagnetism.
Remember when two magnets are brought together they will interact (there will be a force
between them) depending on what poles are brought close together, this is all to do with
the magnetic fields around the magnets. Similarly if you bring a magnet close to the wire
carrying the current there will be an interaction between them. If the magnet is in a fixed
position then it will be the wire that moves and you need to know how the wire will move.
The factors involved are the direction of the current flowing in the wire and the direction of
the magnetic field.
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Figure 14 Using Fleming's left hand rule
Figure 14 shows how you can use Fleming’s left hand rule to find the direction that the wire
will move. Imagine if we looped the wire so that on one side the current flowed in the
opposite direction, what direction would the wire move in? This is the basis of the motor
effect. So if you have a coil of wire connected to a power supply or battery and you place a
permanent magnet outside of the coil, as shown in Figure 14, you have the basic
components of a motor. You need to know how the split-ring commutator, the brushes and
the axle are all vital components for allowing the motor to spin around. What two things
can you do to make a motor go faster? What about if you wanted the motor to spin in
reverse?
Figure 15 A fan and a turbine
Figure 15 shows a fan and a turbine together. Looking at them you should notice certain
similarities but are you aware of the differences? What is needed to make each one spin?
Why do we use each one?
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Not the ‘robots in a disguise’ kind but the kind you met in P but this time you need to be
able to describe how they work – a good opportunity for a 6 mark question. This is a part of
electromagnetism that students often find difficult to understand. Building on your
knowledge that they are used to either increase or decrease the voltage from the primary to
the secondary coil and accordingly decrease or increase the current for energy saving
purposes we will have a quick look at how they do this.
Figure 16 Step up transformer
Figure 16 shows a typical transformer diagram with a primary and secondary coil as well as
an iron core. Students often think that as the core is made of iron and is therefore a
conductor, current can flow from the primary coil to the secondary. Current cannot travel
between the coils through the iron because the wires of the coils are all insulated to prevent
any conduction on the iron core. Why do we have an iron core there? You will notice how it
appears to be layered; we say that it is laminated. What is the significance of the iron core
being laminated?
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How a transformer works
When current flows on the primary coil it produces a magnetic field around it. The iron core
is there to enhance the strength of this magnetic field. This magnetic field is not the same as
one around a permanent magnet where you have one north and one south-pole. The
current in the primary coil is AC (alternating current) which means that it is changing
direction with a certain frequency (50Hz in this country). It follows that the magnetic field
will also alternate – think about it as if the north and south poles are switching between the
top and bottom of the iron core at the same frequency as the alternating current. This
alternating magnetic field on the iron core cuts through the secondary coil. This, in turn,
creates a potential difference on the secondary coil and so an alternating current is able to
flow in the secondary coil. As there are more turns on the secondary coil in Figure 16 this
means the potential difference or voltage is greater on the secondary coil than the primary
coil. If there were less turns on the secondary then the voltage on it would be less and this
would be a step down transformer.
There is an equation associated with transformers relating the power, voltage and current.
A common misconception is that because the secondary coil increases the voltage,
somehow the energy related to it increases. Why is this not the case?
You use at least one type of transformer once a week when charging your phone but also
you will find transformers charging your laptop or other such electrical device. Your phone
charger (transformer) can be carried around in your pocket but your laptop transformer
probably can’t. You need to know the difference between the two types and the term
switch mode transformer as this is a new part of the course.
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Figure 17Earth orbiting the Sun
Imagine if the Sun in Figure 17 suddenly disappeared, what would the earth do – forget
about there being any life on earth to begin with? So what affect does the Sun have on the
earth’s path as it travels through space?
As shown in the diagram when an object travels in a circular path the force causing the
motion always acts towards the centre of the circle. In the case of the earth it is the force of
gravity that causes the circular motion – we call this the centripetal force – the resultant
force that causes circular motion. What causes the centripetal force when a car is going
around a roundabout or if you swing a mass on a string? You need to be able to state how
mass, speed and radius of the circle affect the size of the centripetal force when an object is
displaying circular motion.
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Changing the subject of an equation
Algebra is a branch of Maths that many students find difficult to understand. As Physics is
the application of Maths you will know that there are many requirements of your numeric
ability including the ability to use algebra. One of the biggest difficulties students can have is
changing the subject of an equation, especially if it is not obvious how to employ an
equation triangle to help.
If you have an equation such as
And you wish make A the subject, it is often helpful to use numbers instead of the letters.
Therefore, the equation may be written as
If we want to make 2 the subject (on the left hand side on its own) we need to move the 2
and the 8
First we move the 2, we do this by multiplying both sides by 2
This now gives
This can be simplified as
So by multiplying the right hand side by 2 gets rid of the 2 on the bottom. Notice that both
sides remain equal as 8 x 2 = 16 giving 16 = 16. Now we need to deal with the 8, we have to
divide both sides by 8
This can be simplified as
( )
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Giving
Anything multiplied by 1 is equal to itself so we have
This can be written as
By replacing the numbers with the corresponding letters we now have an equation where A
is the subject
This has been a long method, can you see a simpler way to go from
To
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Standard Form You should be aware that the speed that light travels at is approximately 300000000ms-1
which is a very large number that gets a bit laborious having to write down all the zeros.
Instead we use standard form to simplify this. The standard form of the speed of light is 3
x108ms-1 (3 with 8 zeros behind it).
Often, students have trouble with using their calculators in order to write 3 x108 you use the
following method:
Press ‘3’
Then ‘X10x’ at the bottom of your calculator
Finally press’8’
The ability to use your calculator properly now will mean that you will not have to learn
these skills when you go to study A-Level Science.
Interpreting Graphs Using your knowledge of Maths you should be aware that when you have a graph of a
straight line it is represented in the general form
So if we think about a distance time graph with a straight line through the origin we can see
from the equation relating distance, time and speed
That s is the y component, t is the x component. V is the gradient and there is no c as the
line cuts the y-axis at 0. We would describe the relationship between distance, s, and time,
t, as being directly proportional
To make s equivalent to t we need to add a constant into the equation. In this case, the
constant is the speed, v
If a line does not go through the origin and intercepts the y-axis meaning there is a value for
’c’ we would say that there is a linear relationship between the y and x values.
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Using Significant Figures
Whenever you perform a calculation you may be tempted to write down your answer
exactly as the calculator is showing the number. For example, if you perform the calculation
Not only would this take up time but it is also important to understand that if the numbers
you are dividing only have a certain number of significant figures you can only have
confidence in your answer having a similar number of significant figures.
You need to be able to round the answer to an appropriate number of significant figures (as
opposed to decimal places). As both 13 and 2.4 have two significant figures each, your
answer should also only have two significant figures thus making your answer 5.4. If
however you performed the equation
Your answer would need to have three significant figures and so would be 5.42 (remember
your rules about rounding numbers up and down).
Finally, if the calculation was
Your answer would need to have two significant figures as 2.4 only has two which means
you would not have any confidence in your value beyond two significant figures and so your
answer would be 5.4 again.
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Take a deep breath, relax and make yourself a third lung!
Materials
600ml plastic bottle (cut off the base)
2 large balloons
drinking straw
rubber band
sticky tape
scissors
ball of plasticine (4 cm diameter)
Instructions
Safety: take care cutting the base from the plastic bottle.
1. Remove the neck of one balloon with scissors. Pull the balloon over the bottom of the bottle
and tape the edge of the balloon to the side of the bottle.
2. Place one end of the straw into the other balloon. Attach the balloon to the straw using a
rubber band. Make sure it is tight.
3. Make a hole through the plasticine. Press the straw through the hole. Allow 8 cm of the
straw to extend above the plasticine. Softly squeeze the ball of clay to seal the clay around
the straw.
4. Place the balloon end of the straw into the bottle and use the clay to seal the opening of the
bottle.
5. Slowly pull down on and release the balloon at the base of the bottle. See the balloon inside
the bottle and the air moving in and out of the straw.
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What's going on?
In this model, the straw acts as the trachea, the balloon inside the bottle acts as a lung, the
stretched balloon acts as the diaphragm and the inside of the bottle acts as the thorax.
When you pull down on the ‘diaphragm’ balloon, the volume inside the bottle increases. Because
the volume gets bigger, the air pressure inside the bottle decreases so that it is lower than the air
pressure outside the bottle. Like diffusion, air moves from high pressure to low pressure, so air
rushes into the straw and fills the ‘lung’ balloon. When you breathe in, or inhale, the diaphragm
contracts. The diaphragm in a relaxed state is an upside down U shape. When it contracts it pulls
down and becomes flatter which makes the volume of the chest cavity bigger. Air from outside
enters the airways and fills the lungs.
When you release the ‘diaphragm’ balloon, the volume inside the bottle returns to a smaller
amount. The air pressure inside the bottle then increases so it is higher than the air pressure outside
the bottle. Air rushes out of the ‘lung’ balloon through the straw. When you exhale, the diaphragm
relaxes and makes the volume of the chest cavity smaller. Air leaves the lungs and flows out of the
airways.
Did you know?
In the early and mid-1900s, poliovirus was rife! It works by attacking the central nervous system and
can cause paralysis. In the worst cases, it can paralyse your diaphragms, meaning you couldn’t
breathe. The iron lung was a machine that helped people with paralysed diaphragms to breathe. I
worked by having the patient lying flat on their back with their body inside a chamber and their head
lying on a shelf outside of the chamber. Their neck was surrounded by a sealed rubber collar that
was used to maintain pressure inside the chamber. A pump then changed the air pressure inside the
chamber. As the air pressure inside the chamber changed, it also changed the air pressure inside the
person’s lungs. The mechanism for breathing with the machine is then explained in the same way as
natural breathing.
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GLOSSARY
B3 biological systems
Section B3.1 – Movement of substances Diffusion– Net movement of substances from a high concentration to a low concentration Osmosis– Net movement of water from a high concentration (of water) to a low concentration, through a partially permeable membrane Active transport– Movement of molecules against the concentration gradient, through a membrane (uses energy from respiration) Concentration gradient– The difference in concentration of a substance in two different areas Alveoli– Tiny air sacs in the lungs with very large surface area, allowing oxygen to diffuse into the blood and carbon dioxide to diffuse out Diaphragm– Sheet of muscle across the bottom of the rib cage that increases or decreases the volume of the thorax, playing an important part in breathing and gas exchange Stomata– Tiny holes in the surface of leaves important for exchange of gases Transpiration– The loss of water through leaves via evaporation
Section B3.2 – Transport systems Atria– Upper chambers of the heart, where blood is received Ventricles– Lower chambers of heart Arteries– Blood vessels carrying blood away from heart (usually oxygenated) Veins– Blood vessels carrying blood to the heart (usually deoxygenated) Capillaries– Very small blood vessels only one red blood cell wide, with walls only one cell thick, that carry blood throughout organs Plasma– Liquid part of blood that carries blood cells, carbon dioxide, urea and hormones Red blood cells– Contains haemoglobin and carries oxygen White blood cells– Produce antibodies and destroy pathogens Platelets– Small fragment of cell, that helps blood to clot Xylem– Plant tissue made up of long hollow tubes that act as vessels to transport water Phloem– Plant tissue made of sieve cells and companion cells that transport sugars
Section B3.3 – Homeostasis Urea– Waste product from breaking down excess amino acids in the liver Carbon dioxide– Waste product of respiration Haemodialysis– Blood from patient with kidney failure is passed through dialyser to remove urea and restore normal balance of water, glucose and mineral ions Kidney transplant– Incorporating a healthy kidney from a donor into a patient with kidney failure Antigens– cell marker protein on the outside of cells; different people have different antigens on their cells Thermoregulatory centre– Part of brain that monitors and controls core body temperature Dilate– Become wider Constrict– Become narrower Shivering– small rapid contractions by the muscle to generate heat Hormone– Chemicals produced by glands, transported in blood and acts on target cells e.g. Insulin and glucagon Glucose– Simple sugar used in respiration to release energy Glycogen– Storage molecule of glucose in muscle and liver cells Tyoe1 Diabetes– Diabetes cause by an inability of the pancreas to produce insulin
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Section B3.4 – Humans and their environment Biodiversity – Variety of living organisms Global warming – Increase in global temperatures attributed to higher levels of carbon dioxide in the atmosphere Carbon Neutral – Whilst plants release CO2 as they burn, they also absorb CO2 in photosynthesis Biofuel– Fuels made from the anaerobic fermentation of plant material using yeast (ethanol) Biogas– Fuels made from the anaerobic fermentation of plant material found in manure, mainly methane gas. Fermentation – One kind of anaerobic respiration Fusarium– Fungus used to make mycoprotein products such as quorn
C3 – The periodic table, water, energy change, chemical analysis, ammonia, alcohols, esters and carboxylic acids
Section C3.1 – the periodic table Atoms – The smallest part of an element that still retains the properties of that element Atomic number – the number of protons in the nucleus (also called the proton number) Groups – A vertical column of elements in the periodic table Period – A horizontal row of elements in periodic table Alkali metals – Elements of group 1 in the periodic table Transition elements – The large block of metal elements in the centre of the periodic table Halogens – Group 7 elements in the periodic table Oxidation – A reaction involving the loss of electrons Reduction – A reaction involving the addition of electrons
Section C3.2 – Water Water softener - Apparatus that contains ion exchange resins that remove calcium and magnesium ions from water Hard water – tap water that contains dissolved compounds that form “scum” with soap Soft water – water that does not contain dissolved substances that produce scum and scale Precipitate – A solid material (insoluble salt) produced from a solution
Section C3.3 – Calculating energy change Fuel – A chemical that is burned to release heat energy Endothermic – the energy needed to break existing bonds is greater than the energy released in forming new bonds i.e. a reaction that takes in energy from the surroundings Exothermic – the energy released from forming new bonds is greater than the energy needed to break existing bonds i.e. a reaction that releases energy to the surroundings
Q = mcT – energy change is equal to mass (m) x specific heat capacity of water (c) x change in
temperature (T) Combustion – The process of burning Bomb calorimeter - Apparatus used to make accurate measurements of energy changes in reactions
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Section C3.4 & 3.5 – Analysis and quantitative chemistry & making ammonia Flame test – A technique to identify group 1 and 2 metal ions by analysing its flame colour Titration – A technique used to measure the precise volumes of acid and alkali solutions needed to react with each other Pipette – Apparatus used to measure a fixed volume of solution Burette- Apparatus used to measure the volume of solution added Reversible reaction – A reaction in which the products immediately react together to produce the original reactants Yield – The amount of product formed in a chemical reaction Optimum conditions – the most ideal conditions needed to produce that maximum yield Haber process – The industrial process used to make ammonia (NH3)
Section C3.6 – Alcohols, carboxylic acids and esters Organic substances – compounds that are based on the element carbon Alcohols – Any organic molecules that contains the –OH group Carboxylic acids – An organic compound that is weakly acidic containing the –COOH group Esters – An organic compound that has the functional group –COO- which usually have a distinctive (sweet) smell Volatile – compounds that have a tendency to turn into a gas easily
P3 – Further Physics
Section P3.1 – Medical applications of physics Concave lens – a lens thinner in the middle than at the rim. It is a diverging lens, which means parallel beams of light spread out (diverge) Convex lens – thicker in the middle than at the rim. It is a converging lens, which focuses parallel rays of light onto a point X-ray – Part of the electromagnetic (EM) spectrum with a wavelength similar to the diameter of an atom; They are absorbed by metal and bone but transmitted through healthy tissue. Can be detected using photographic plates CT Scan – Coputerised Tomography Scan – a series of X-Ray images compiled on a computer to form a 2D or 3D image Ultrasound – Sound above the range of human hearing (20kHz), used for pre-natal scanning, and removal of kidney stones
Hert (Hz) – Unit of frequency equivalent to
Refraction – When waves change direction and speed when going into a medium (substance) of different density (e.g. light going from air into glass) Refractive index = sin i ÷ sin r (where i is the angle of incidence, and r is the angle of refraction) Magnification – Where the image size is larger than the original object Power of a lens = 1/f, where f is the focal length Real image – An image through which light rays pass, so that it can be seen on a screen placed at that point Virtual image – an image that light rays do not pass through; they only appear to come from the image Ciliary muscle – controls the shape of the lens in the eye Inverted Image – an upside down image
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Fibre optic – a cable made of glass used to transmit data by light using total internal reflection
Section P3.2 – Using physics to make things work Stable – When the line of action of the centre of mass goes through an object’s base Time period – time taken for a pendulum to return to the point of release (T = 1/f, where f is the frequency in Hz) Moment – Turning force (M, the moment = F x d, where F is the force applied and d is the perpendicular distance from the pivot) Pivot – Point around which an object moves Hydraulics – transferring a force from one place to another; relies on the fact that liquids are incompressible Pressure- calculated by dividing force by area Centripetal force – The force that acts towards the centre when an object moves in a circular motion (e.g. gravitational force when a planet orbits the sun)
Section P3.3 – Keeping things moving Conductor – A material which allows an electrical current to flow through it e.g. metals Insulator – A material which does not allow a current to flow through it e.g. wood Transformer – A component consisting of two copper coils around an iron core which changes the potential difference of an AC power supply Switch Mode Transformer – a small transformer that switches current on and off at a high frequency Step up transformer – An electrical component that increases voltage and decreases current so that less energy is lost through heating when it is transferred through power cables Step down transformer – An electrical component that decreases voltage and increases current for use in homes Motor effect – The force experienced by a wire carrying a current which is placed in a magnetic field Electromagnetic induction – When a conductor (e.g. a wire) is moved in a magnetic field, a current is produced along the wire. Electromagnet – a magnet made when an electric current flows through a wire which is wrapped around an iron core Fleming’s Left Hand Rule – a way of understanding the direction of force on a current carrying in a magnetic field
