Oxford Revise AQA GCSE Chemistry | Chapter C6 answers

C6: Chemical calculations with mass

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Answers

Extra information

Mark

AO / Specification reference

01.1

12 + (4 × 1) = 16

1

AO2

4.3.1.2

01.2

the reactant that is completely used up when the other reactant is present in excess

1

AO1

4.3.2.1

01.3

CH4 + 2O2 → CO2 + 2H2O

2

AO2

4.3.1.1

01.4

oxygen

1

AO2

4.3.2.4

01.5

0.25

1

AO2

4.3.2.4

02.1

6.02 × 1023 × 6

= 3.61 × 1024

1

1

AO1

4.3.2.1

02.2

164

1

AO2

4.3.1.2

02.3

gaseous products leave the test tube as a gas

allow named gas (oxygen or nitrogen dioxide).

1

AO2

4.3.1.3

02.4

CaO: (40 + 16) = 56

\(\frac{22.4}{56}\)

= 0.4 mol

0.4 × 164

= 65.6g 6.02 × 1023

1

1

1

1

1

AO1 × 1

AO2 × 4

4.3.2.2

03.1

mass of one mole of water = RMM of H2O = 16 + (2 × 1) = 18

answer states for water, 1 g = 1 cm3, so 1 mole = 18 g = 18 cm3

1

1

AO2

4.3.2.1

03.2

\(\frac{18}{6.02 \times 10^{23}}\)

= 2.99 × 10–23 g

1

1

AO2

4.3.2.1

03.3

answer assumes that all particles in the 18 cm3 is taken up by water particles

but water is a liquid, so has space between the particles

1

1

AO3

4.3.2.1

04.1

there are three atoms of oxygen for every one atom of sulfur

1

AO2

4.1.1.1

04.2

32 + (2 × 16) = 64

accept correct answer without working shown

1

AO2

4.3.1.2

04.3

1.68 – 1.28 = 0.4 g

accept correct answer without working shown

1

1

AO1

4.3.1.1

05.1

the number of atoms, molecules or ions in a mole of a given substance

accept ‘particles’ in place of ‘atoms’, ‘molecules’ or ‘ions’

accept mention of just one or two of atoms, molecules or ions.

1

AO1

4.3.2.1

05.2

Mr of water = (2 × 1) + 16 = 18

\(
{\rm{number\ of\ moles\ of\ water}} = \frac{{23}}{{18}} = 12.89{\rm{\ mol}}
\)

number of molecules = 12.89 × 6.02 × 1023

= 7.76 × 1024

1

1

1

1

1

AO2

4.3.2.1

05.3

\(\frac{464}{232} = 2\)

2 × 7.76 × 1024 = 1.55 × 1025

1

1

AO2

4.3.2.1

06.1

one from

  • wear eye protection
  • work in a fume cupboard

accept any other reasonable answer.

1

AO3

WS2.4

06.2

2Na(s) + Cl2(g) → 2NaCl(s)

one mark for balancing

one mark for state symbols

2

AO2

4.3.1.1

4.2.2.2

06.3

Level 3: The description is detailed and accurate. The writing is clear, coherent and logical.

5-6

AO1

4.2.1.2

4.2.1.3

Level 2: The description is correct, although lacks detail. The writing is mainly clear, although the structure may lack logic.

3-4

Level 1: Some aspects of the description are correct. The writing lacks clarity, coherence and logic.

1-2

No relevant content.

0

Indicative content

  • sodium atoms each lose one electron to make Na+ ions.
  • chlorine atoms each gain one electron to make Cl ions.
  • the oppositely charged ions are held together
  • in a lattice
  • by strong electrostatic forces of attraction
  • that act in all directions.

07.1

\(\frac{52 + 49 + 48 + 56 + 55}{5} = 52\)

1

AO2

MS2b

07.2

56 – 48 = 8

1

AO2

4.3.1.4

07.3

\(
\begin{array}{l}
{\rm{uncertainty}} = \frac{\rm{range}}{2}\ =\ \frac{8}{2} = 4\\
{\rm{mean}} \pm 4
\end{array}
\)

1

AO2

4.1.3.4

07.4

\(
7.3 \times \frac{{25}}{{1000}}
\)

= 0.1825

= 0.18

1

1

1

AO2

4.3.2.5

08.1

HNO3(aq) + KOH(aq) → KNO3(aq) + H2O(l)

1

AO2

4.2.2.2

08.2

\(
\begin{array}{l}
\frac{14}{700} \times 1000\\
= 20{\rm{\ g/d}}{{\rm{m}}^3}
\end{array}
\)

allow 0.02 g/cm3 if units are specified.

1

1

AO2

4.3.2.5

08.3

\(
\begin{array}{l}
22 \times \frac{{30}}{{1000}}\\
= 0.66{\rm{\ g}}
\end{array}
\)

1

1

AO2

4.3.2.5

08.4

\(
\begin{array}{l}
{\rm{moles\ HN}}{{\rm{O}}_3} = \frac{{0.66}}{{63}}\\
= 0.01\\
20 \times \frac{{35}}{{1000}}\; = 0.7g\\
{\rm{moles\ KOH}} = \;\frac{{{\rm{0}}{\rm{.7}}}}{{{\rm{56}}}}\\
= 0.0125\\
{\rm{since\ moles\ HN}}{{\rm{O}}_3} \lt {\rm{\ moles\ KOH,\ limiting\ reagent}} = {\rm{HN}}{{\rm{O}}_3}
\end{array}
\)

1

1

1

1

1

1

AO2

4.3.2.5

09.1

first N atom should have 2 shells with 2 crosses in first shell and 5 crosses in second shell, second N atom should be the same but with dots.

the N atoms should be sharing 3 dot and 3 cross electrons in an alternating pattern.

2

AO2

4.2.1.4

09.2

gas would build up in the tube, as it has nowhere to escape to

this may result in the bung being forced out of the test tube

1

1

AO3

WS2.3

WS2.4

09.3

\(
\begin{array}{l}
{\rm{number\ of\ moles\ of\ Mg}} = \frac{{2.16}}{{24}} = 0.09\\
{\rm{number\ of\ moles\ of\ }}{{\rm{N}}_2} = \frac{{0.84}}{{(2 \times 14)}}\; = 0.03\\
{\rm{number\ of\ moles\ of\ M}}{{\rm{g}}_3}{{\rm{N}}_2} = \frac{{3.00}}{{(3 \times 24) + (2 \times 14)}} = 0.03\\
0.09{\rm{\ Mg}} + 0.03{{\rm{\ N}}_2} \to 0.03{\rm{\ M}}{{\rm{g}}_3}{{\rm{N}}_2}\\
3{\rm{\ Mg}} + {{\rm{N}}_2} \to {\rm{M}}{{\rm{g}}_3}{{\rm{N}}_2}
\end{array}
\)

1

1

1

1

1

AO2 × 3

AO3 × 2

4.3.2.3

10.1

\(
1{\rm{\ d}}{{\rm{m}}^3} = 1000{\rm{\ c}}{{\rm{m}}^3},{\rm{\ so\ }}\frac{{1000{\rm{\ c}}{{\rm{m}}^3}}}{{5{\rm{\ c}}{{\rm{m}}^3}}} = 200
\)

500 mg × 5 = 2500 mg in 1 dm3

0.5g/dm3

1

1

1

AO2

WS4.3

WS4.4

WS4.5

4.3.2.5

10.2

(8 × 12) + (9 × 1) + 14 + (2 × 16) = 151 g

1

AO2

4.3.1.2

10.3

Mr of ibuprofen = (13 × 12) + (18 × 1) + (2 × 16) = 206

\(
{\rm{number\ of\ moles\ in\ }}5.0{\rm{\ c}}{{\rm{m}}^3}{\rm{of\ solution\ }} = \frac{{0.1}}{{206}} = 0.000485
\)

number of moles in 1000 cm3 of solution = 0.000 485 × 200

= 0.0971 moles

or 9.71 × 10–2 mol in standard form

final mark awarded for giving answer to 3 significant figures

1

1

1

1

AO2

4.3.2.1

4.3.2.5

MS2a

11.1

(4 × 12) + (2 × 1) + 56 + (4 × 16) = 170

1

AO2

4.3.1.2

11.2

Mr = 56 + 32 + (4 × 16) = 152

\(
{\rm{number\ of\ moles}} = \frac{0.1}{206}
\)

= 4.3 × 10–4 moles

one mark awarded for giving answer to two significant figures; one mark for correctly expressing answer in standard form

1

1

2

AO2

4.3.2.1

MS1b

11.3

Mr = (12 × 12) + (24 × 1) + 56 + (14 × 16) = 448

\(
{\rm{number\ of\ moles\ of\ iron\ gluconate}} = \frac{{0.3}}{{448}} = 0.000670
\)

number of moles of iron = 0.000 670

mass of iron = 0.000 670 × 56 = 0.0375 g

or 37.5 mg if correct units are given

1

1

1

1

AO2 × 2

AO3 × 2

4.3.2.1

MS2a

12.1

Mr of iron oxide = (56 × 2) + (3 × 16) = 160

\(
16{\rm{\ g}} = \frac{{16}}{{160}} = 0.10{\rm{\ mol}}
\)

0.10 moles of Fe2O3 reacts with 0.15 moles of C

12 × 0.15

= 1.8 g

1

1

1

1

1

AO2

4.3.2.2

12.2

number of moles of CO2 = number of moles of C = 0.15

Mr of CO2 = 12 + (2 × 16) = 44 g

mass of CO2 = 0.15 × 44 g

= 6.6 g

1

1

1

1

AO2

4.3.2.2

12.3

3.7 tonnes = 3700 kg

\(
\frac{{{\rm{3700}}}}{{{\rm{160}}}}
\)

= 23.125 moles

23.125 × 2 = 46.25 moles of Fe

46.25 × 56

= 2590 kg

1

1

1

1

1

1

AO2

4.3.2.2

12.4

\(\frac{2590}{3700} \times 100\)

= 70%

\(\rm{allow\ }56 \times \frac{2}{160}\; \times 100\)

1

1

AO2

13.1

wear eye protection

work in a fume cupboard

1

1

AO1

WS2.4

13.2

fill the gas jar with chlorine gas first

so that the chlorine does not escape before the sodium is added to it

1

1

AO3

WS2.4

13.3

Na ion should have 2 shells with 2 crosses in the first shell, 8 crosses in second shell. Should be in square brackets with a superscript ‘+’ to the right of the brackets.

Cl ion should have 3 shells with 2 dots in the first shell, 8 dots in the second shell and 7 dots and 1 cross in square brackets. Should be in square brackets with a superscript ‘+’ to the right of the brackets.

2

AO1

4.2.1.2

three from:

  • ionic bonding
  • sodium atom transfers 1 electron to chlorine atom
  • forming 1+ sodium ion and -1 chlorine ion
  • electrostatic attraction between oppositely charged ions

one mark for each correct point

3

AO1

4.2.1.2

13.5

sodium conducts electricity

because it contains delocalised electrons that can move

chlorine does not conduct electricity

because it does not contain charged particles that can move

sodium chloride conducts electricity when in solution or molten, but not when solid

because ions are free to move

1

1

1

1

1

1

AO1

4.2.1.3

4.2.1.4

4.2.1.5

13.6

at the start, orange-brown liquid instead of green gas during/reaction would be less vigorous

1

AO1

4.1.2.6

14.1

P atom should have 3 shells, first shell should have 2 crosses, second shell should have 8 crosses and 3 shell should have 5 crosses

1

AO1

4.1.1.7

14.2

five

1

AO3

4.1.2.1

14.3

Level 3: The properties and locations are correctly given. The comparisons are clear, coherent and logically expressed.

5-6

AO1

4.1.1.5

4.1.1.4

Level 2: The properties and locations are mainly correct. The comparisons are mainly clear, but there is a lack of logic in the answer.

3-4

Level 1: Some of properties and/or locations are correct. The writing lacks clarity, coherence and logic, and only one or two comparisons are made.

1-2

No relevant content.

0

Indicative content

  • protons have a charge of +1 and a relative mass of 1
  • neutrons have no charge and a relative mass of 1
  • electrons have a charge of −1 and a very small relative mass
  • protons and neutrons are found in the nucleus of an atom
  • electrons are found outside the nucleus
  • electrons are in orbits/shells/levels
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