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