View
216
Download
0
Category
Preview:
Citation preview
NATIONAL 5 - CHEMISTRY
CHEMICAL CHANGES AND STRUCTURE
ANSWERS HOMEWORK 1 - RATES OF REACTION
1a) Decreasing the particle size of a reactant results in an increase in the
surface area this will expose more particles that will be available to allow
collisions to occur. More product will be formed as a result of the higher
frequency of collisions being allowed to occur.
b) Decreasing the concentration results in a slowing of reaction rate because
less particles will be present resulting in a lower frequency of collisions
occurring and this will mean less chance of product forming.
c) Increasing the temperature that a reaction is taking place will mean the
particles have greater kinetic energy. This increased kinetic energy of particles
will result in a greater frequency of collisions between reactant particles and
therefore more chance of product forming and an increase in rate of reaction.
2a) i) Test tube A has magnesium ribbon in comparison to test tube B having
magnesium powder. The reaction will be quicker in test tube B because of the
reduced particle size giving an increased surface area, with more particles
available for collision the reaction rate will be higher in test tube B.
ii) Test tube C in comparison to test tube A will have a slower rate of reaction
because the concentration of acid is lower meaning less chance of reactant
particles colliding meaning a slower rate of reaction.
b) Increasing the temperature results in the reactant particles having more
kinetic energy, increasing frequency of collisions and a faster rate of reaction.
C) a. A catalyst speeds up a chemical reaction.
b. They are not used up during the reaction and can be recovered
and reused.
c. A catalytic converter is a solid catalyst made of platinum that allows
harmful gases to be adsorbed onto the surface of the catalyst. These harmful
gases e.g. carbon monoxide, nitrogen oxides by being absorbed onto the surface
of the catalyst results in their bonds being weakened. More oxygen and nitrogen
from the air can then react with these harmful gases producing less harmful
gases that are then desorbed from the catalyst and expelled out the exhaust of
the car. Gases such as nitrogen, carbon dioxide etc. (less harmful).
3) a) As time increases the pressure (bar) also increases.
b) Graph – an appropriate scale on the x and y axis
- labels with units on the x and y axis
- points are plotted correctly
- Tread line is added that best represents the results.
HOMEWORK 2 - RATES OF REACTION
1a) hydrogen
b) Average rate of reaction = Change ÷ Time
= 72 cm3 ÷ 40 s
= 1.8 cm3 s-1
c) 58 s or 60 s
d) The reaction would be faster because of the increased rate of reaction due
to the increase in concentration of sulphuric acids used. More particles present
in which to increase the frequency of collisions and therefore faster rate of
reaction.
e) On the graph provided you should have shown a steeper gradient at the start
showing more product formed within a shorter time but since the same
magnesium ribbon is being used then the reaction should curve (indicating the
reaction is slowing due to reactant concentration decreasing as product is
forming) and the curve should flatten at 82 cm3 of hydrogen gas produced but
much sooner than the curve already present on the graph.
2a) 0 to 2 minutes
Average rate = change ÷ time
= (128.7 cm3 – 128.4 cm3) ÷ 2 min
= 0.3 cm3 ÷ 2 min
= 0.15 cm3 min -1
2 to 4 minutes
Average rate = change ÷ time
= (128.4 cm3 – 128.33 cm3) ÷ 2 min
= 0.07 cm3 ÷ 2 min
= 0.035 cm3 min -1
4 to 6 minutes
Average rate = change ÷ time
= (128.33 cm3 – 128.30 cm3) ÷ 2 min
= 0.03 cm3 ÷ 2 min
= 0.015 cm3 min -1
b) 0.1g
c) The mass loss is greatest at the start of the reaction because the reactant
concentration is the highest and this means that more frequency of collisions
will occur in which will result in product being formed. As product forms then
the reactant concentration decreases and thus less frequency of collision and
therefore as the reaction time proceeds the rate decreases until eventually all
reactant particles have collided and formed product.
HOMEWORK 3 - ATOMIC STRUCTURE
Q1) a) Nucleus
b) i) mass number = 8
ii) Proton number equals electron number within an atom.
iii) alkali metals because the atom being shown has an electron arrangement 2,1.
2a) atomic number = 6
b) mass number = 14
c)
d) electrons = 6
3)
Symbol Number
of protons
Number of
neutrons
Number of
electrons
Atomic
number
Mass number
4
He
2
2
2
2
2
4
12
C
6
6
6
6
6
12
6
8
6
6
14
16
O
8
8
8
8
8
16
8
9
8
8
17
54
Fe
26
26
28
26
26
54
26
30
26
26
56
4) oxygen, carbon and iron are isotopes shown above.
5) The two statements that are correct are B and D.
HOMEWORK 4 - ATOMIC STRUCTURE
Q1)
Element Electrons Protons Neutrons
10 9 10
18 19 20
10 8 8
10 10 10
10 13 14
18 20 20
10 12 12
Q2) a) Isotopes are atoms with the same atomic number but a different mass
number. e.g.
b)
Isotope Number of
protons
Number of
neutrons
Number of
electrons
47 60 47
C) Relative atomic mass = [(107 x 48%) + (109 x 52%)] ÷ 100
= [5136 + 5668] ÷ 100
= 10804 ÷ 100
= 108.04
d) An elements relative atomic mass is an average of an elements isotopes.
3) a) (31 ÷ 100) x 2500 = 775 ions
b) average = (4 + 6.7 + 5.5 + 4.8 + 4.2) ÷ 5
= 25.2 ÷ 5
= 5.04
HOMEWORK 5 – BONDING RELATED TO PROPERTIES
Q1) A covalent bond is a shared pair of electrons between two positive nuclei.
Q2) a) Ammonia, NH3
b) Water, H2O
Q3) Ammonia – Pyramidal
Water – Bent or angular
Q4) C) Chlorine as it is diatomic
Q5) a) An ionic bond is an electrostatic interaction between a positive and
negative ion when usually a metal atom has lost electrons and a non-metal atom
has gained electrons to have an electron arrangement similar to a noble gas.
2, 8, 1 2,8,7
C) B – There are no chemical changes at the electrodes – this is the statement
that is not correct.
HOMEWORK 6 – BONDING RELATED TO PROPERTIES
A) Covalent network – network of strong
covalent bonds only.
– have high melting and boiling point.
- does not conduct in any state with carbon in
the form of graphite the exception.
- does not dissolve in water
- examples include carbon (diamond, graphite
etc.), silicon dioxide.
B) Ionic lattice – oppositely charged ions in a
lattice structure
– have high melting and boiling point.
- conducts only when molten or dissolved in
solution
- examples include sodium chloride, magnesium
oxide etc.
C) Covalent molecular – small discrete
molecules with weak forces between them.
– have low melting and boiling point.
- does not conduct in any state.
- Strong bonds within molecules and weak forces
of attraction between molecules
- examples include carbon dioxide, ammonia
D) Metallic bonding – positive metal ions
surrounded by delocalised electrons
– have high melting and boiling point.
- conducts electricity in any state
- does not dissolve in water
- examples include any metal left of the stair
case on the periodic table.
Q2) a) A, F
b) B, H
c) C, I
d) D, E
Q3) A) Covalent molecule
B) Metallic bonding
C) Covalent network
D) Ionic bonding
E) Metallic bonding
F) Covalent molecule
Q4) A) Molten ionic compounds
B) Solid ionic compounds
Q5) The graphite structure can conduct electricity because all thought being a
covalent network it is the only one with delocalised electrons that can carry a
current of electricity through the molecule. These delocalised electrons are
between layers and explains the function of graphite in a pencil that these weak
forces between layers having delocalised electrons allow the layers to come
apart onto the paper when you write with a pencil.
HOMEWORK 7 – FORMULA AND REACTION QUANTITIES
Q1) a) Na2O b) BaBr2 c) Mg3N2 d) CF4 e) NH3 f) N2O4
Q2) a) Li+NO3- b) Ca2+CrO4
2- c) (K+)3PO43-
d) Ag+I- e) Zn2+(OH-)2 f) (Fe3+)2(SO42-)3
g) (Al3+)2(O2-)3 h) Mg2+ (Cl-)2 i) Al3+(F-)3
Q3)
a) Na3PO4 + 3KOH 3NaOH + K3PO4
b) MgF2 + Li2CO3 MgCO3 + 2 LiF
c) P4 + 3O2 2 P2O3
d) 2RbNO3 + BeF2 Be(NO3)2 + 2RbF
e) 2AgNO3 + Cu Cu(NO3)2 + 2Ag
f) CF4 + 2 Br2 CBr4 + 2F2
g) 2HCN + CuSO4 H2SO4 + Cu(CN)2
h) GaF3 + 3Cs 3CsF + Ga
(i) N2 + 3H2 2NH3
Q4) SiO2
Q5) potassium – lilac
Strontium – red
Copper – blue/green
Barium – green
HOMEWORK 8 – FORMULA AND REACTION QUANTITIES
Q2) Soluble Insoluble
154
138.5
310
296.5
136.5
310
342
140.5
Calcium bromide Nickel hydroxide
Silver sulphate Aluminium Phosphate
Tin(ii) Sulphate Calcium Carbonate
Lead(ii) Iodide Barium hydroxide
Q3) (a) How many moles of barium chloride, BaCl2, are present in 4.166g of the
salt?
n = m ÷ gfm
= 4.166 ÷ 208.5
= 0.02 moles
(b) What is the mass of 1.2 mol of sodium hydroxide, NaOH?
m = n x gfm
= 1.2 x 40
= 48g
(c) What is the mass of 0.2 mol of copper(ii) chloride, CuCl2?
m = n x gfm
= 0.2 x 134.5
= 26.9g
(d) How many moles of nitric acid, HNO3, are present in 94.5g of the pure
substance?
n = m ÷ gfm
= 94.5 ÷ 63
= 1.5 moles
(e) What is the mass of 0.025 mol of iron(iii) oxide, Fe2O3?
m = n x gfm
= 0.025 x 160
= 4g
(f) How many moles of silver(i) nitrate, AgNO3, are present in 6.796g of the
substance?
n = m ÷ gfm
= 6.796 ÷ 170
= 0.04 moles
(g) The balanced equation shown below:
CaO + 2HCl CaCl2 + H2O
According to this balanced equation, the mass of calcium chloride that 0.2 mol
of calcium oxide will produce is
A) 22.2g B) 111g C) 11.2g D) 37.5g
Answer with showing working:
CaO + 2HCl CaCl2 + H2O
1 mol 2 mol 1 mol 1 mol
0.2 mol 0.2 mol
m = n x gfm
= 0.2 x 111
= 22.2g
MOLE
RATIO
(4) (a) Calculate the no. of moles present in 50cm3 of 0.05 molar HCl.
n = c x v
= 0.05 x 0.05
= 0.0025 moles
(b) Calculate the concentration of a glucose solution, given that 0.2 moles of
glucose are dissolved in water and made up to 250 cm3 of solution.
c = n ÷ v
= 0.2 ÷ 0.25
= 0.8 mol L-1
(c) Calculate the concentration of a solution of calcium hydroxide given that it
contains 1.48g of Calcium hydroxide in 800 cm3 of solution.
(d) Calculate the volume of solution produced if 22.5g of Oxalic acid (COOH)2, is
used to make a solution with concentration 0.5 mol L-1.
(e) A 330 cm3 can of “Fizz Alive” has a carbohydrate concentration of 0.01
mol/l. Calculate the number of moles of carbohydrate in the can of “Fizz Alive”.
n = c x v
= 0.01 x 0.33
= 0.0033 moles
Q5) (a) Calculate the mass of hydrogen produced when 4.9g of magnesium
reacts with an excess of dilute sulphuric acid.
(b) Urea reacts with water, breaking down to form carbon dioxide and ammonia.
Calculate the mass of ammonia produced, in grams, when 90g of urea
breaks down.
(c) The neutralisation reaction shown below was carried out in the laboratory.
The chemist used 1g of calcium carbonate and reacted it with excess dilute
hydrochloric acid. Calculate the mass of carbon dioxide produced.
(d) The equation below shows the breakdown of glyceryl tristearate to form
glycerol and stearic acid. Calculate the mass of stearic acid produced from 8.9g
of glyceryl tristearate.
(e) Ammonium sulphate is a commonly used fertiliser. It can be produced by the
reaction between ammonium carbonate and calcium sulphate. What mass of
ammonium carbonate, (NH4)2CO3, would be needed to make 13·2 kg of ammonium
sulphate, (NH4)2SO4?
HOMEWORK 9 – ACIDS AND BASES
Q1) a)
b) The solution would contain more hydrogen ions than hydroxide ions resulting
in the solution being acidic and explaining the pH 5.
c) It would be a metal oxide such as sodium oxide that would dissolve producing
a metal hydroxide such as sodium hydroxide and this increasing the
concentration of hydroxide ions and giving a pH of 9. The metal oxide would
have to be soluble of course.
d) Calculate the mass of sodium nitrate required to prepare 250cm3 of 0.1 mol
l-1 solution
e) What will be the concentration of 200cm3 of a solution containing: 4.8g of
LiOH
Q2)
(a) Sodium hydroxide + sulphuric acid sodium sulphate + water
(b) Potassium oxide + nitric acid potassium nitrate + water
(c) Calcium carbonate + hydrochloric acid calcium chloride + water + CO2
(d) magnesium carbonate + hydrochloric acid magnesium chloride + water + CO2
(e) Aluminium + sulphuric acid Aluminium sulphate + hydrogen
- because hydrogen is produced then it can only be aluminium metal reacting not
aluminium hydroxide.
Q3) 3 marks: The maximum available mark would be awarded to a student who
has demonstrated a good understanding of the chemistry involved. The student
shows a good comprehension of the chemistry of the situation and has provided
a logically correct answer to the question posed. This type of response might
include a statement of the principles involved, a relationship or an equation, and
the application of these to respond to the problem. This does not mean the answer
has to be what might be termed an “excellent” answer or a “complete” one.
2 marks: The student has demonstrated a reasonable understanding of the
chemistry involved. The student makes some statement(s) which is/are relevant
to the situation, showing that the problem is understood.
1 mark: The student has demonstrated a limited understanding of the chemistry
involved. The candidate has made some statement(s) which is/are relevant to the
situation, showing that at least a little of the chemistry within the problem is
understood.
Q4) B – sodium hydroxide because when metal oxides dissolve they produce
alkaline solutions, copper (ii) oxide is insoluble so cannot produce a solution and
the other two non-metal oxides dissolve to give acidic solutions.
Q5) a) F – (OH-)
b) D – (H+)
c) A + F – (Al3+) and (OH-)
Q6) B + E
HOMEWORK 10 – ACIDS AND BASES
1. What volume of potassium hydroxide solution (concentration 2mol/l) is
required to neutralise 50 cm3 sulphuric acid (concentration 1 mol/l).
2. What volume of nitric acid (concentration 0.5 mol/l) is required to neutralise
25 cm3 sodium hydroxide solution (concentration 4mol/l).
3. If 25 cm3 hydrochloric acid is neutralised by 50 cm3 sodium hydroxide
solution (concentration 2 mol/l), what is the concentration of the acid?
4. If 100 cm3 of nitric acid is neutralised by 30.3 cm3 sodium hydroxide
(concentration 1 mol/l), what is the concentration of the acid?
Q5) A spectator ion is an ion that exists in the same form on both the reactant
and product sides of a chemical reaction.
Q6) An ion equation shows electrons being gained and lost with respect to a
reaction and shows the respective charges on the ions involved.
Q7) e.g hydrochloric acid + sodium hydroxide sodium chloride + water
H+Cl- + Na+OH- Na+Cl- + H2O
Q8) e.g hydrochloric acid + calcium carbonate calcium chloride +water + CO2
2H+Cl- + Ca2+CO32- Ca2+(Cl-)2 + H2O + CO2
Q9)
i) K+OH- + H+Cl- K+Cl- + H2O
ii) H+ + OH- H2O
the reaction of lithium hydroxide solution with dilute sulphuric acid
i) 2Li+OH- + (H+)2SO42- (Li+)2SO4
2- + 2H2O
ii) 2H+ + 2OH- 2H2O
the reaction of lithium carbonate solution with dilute sulphuric acid
i) (Li+)2CO32- + (H+)2SO4
2- (Li+)2 SO42- + H2O +CO2
ii) 2H+ + CO32- H2O + CO2
the reaction of potassium carbonate solution with dilute nitric acid
i) (K+)2CO32- + 2H+NO3
- 2K+NO3- + H2O + CO2
ii) 2H+ + CO32- H2O + CO2
the reaction of potassium hydroxide solution with dilute hydrochloric acid
Q10) Name the spectator ions in the following reactions?
a. 2H+Cl-(aq) + Mg2+CO32-
(s) Mg2+(Cl-)2(aq) + H2O(l)
Mg2+ and Cl-
b. 2H+Cl-(aq) + Zn2+O2-(aq) Zn2+(Cl-)2(aq) + H2O(l)
Zn2+ and Cl-
(NH4+)2CO3
2-(aq) + Mg2+SO4
2-(aq) Mg2+CO3
2-(s) + (NH4
+)2SO42-
(aq)
NH4+ and SO4
2-
(Q11) Electronegativity is a measure of the attraction that an atom has for the
bonded electrons. The chart below shows the electronegativity values for some
elements in the periodic table.
(a) Describe what happens to the elctronegativity values going across a period in
the periodic table. - Going across a period in the periodic table showe the
electronegativity increases.
(b) Draw a bar on the chart to predict the electronegativity value for the
element calcium, atomic number 20.
Skill Q
Recommended