Edexcel IAL Chemistry AS Topic 1 Question Bank

[Maximum number: 6]

Terpenes and terpenoids are groups of chemicals found in plants.
They contribute to the smell and taste of the plant, and so are used in flavourings and perfumes.

Both terpenes and terpenoids have carbon skeletons based on one or more units of the compound isoprene.

Figure for Question 1 — Edexcel A-Level Chemistry AS

isoprene
Terpenes are made up of two or more isoprene units joined together, while terpenoids have additional functional groups, often containing oxygen.

Limonene and myrcene are both terpenes composed of two isoprene units.
Menthol, linalool and citronellol are terpenoids containing an - OH group.

(a)

Show that myrcene and limonene are terpenes by comparing the molecular and/or empirical formulae of myrcene, limonene and isoprene.

myrcene

limonene

isoprene

[ 2 ]

An answer that makes reference to the following points:

- molecular formula of either myrcene, limonene or both is $\mathrm{C}_{10} \mathrm{H}_{16}$ and the molecular / empirical formula of isoprene is $\mathrm{C}_{5} \mathrm{H}_{8}$

- so the molecular formula of myrcene and limonene is twice isoprene (so they are terpenes)

OR

- molecular formula of either myrcene, limonene or both is $\mathrm{C}_{10} \mathrm{H}_{16}$ and the molecular / empirical formula of isoprene is $\mathrm{C}_{5} \mathrm{H}_{8}$

- so the empirical formula of myrcene and limonene is the same as isoprene (so they are terpenes)

(b)

5 g samples of myrcene and limonene were completely hydrogenated. Calculate the volume of hydrogen required to hydrogenate each sample.

Include the unit with your answer.

Assume the volume of 1 mol of hydrogen $=24000 \mathrm{~cm}^{3}$

[ 4 ]

Stand alone first mark

- calculation of $M_{\mathrm{r}}$ of terpene and moles of terpene

(1)

Method 1

- either value for number of moles of $\mathrm{H}_{2}$

(1)

- either volume of $\mathrm{H}_{2}$

(1)

- second volume of $\mathrm{H}_{2}$ with unit

(1)

Method 2

- either value for one $\mathrm{H}_{2}$ per terpene

(1)

- either volume of $\mathrm{H}_{2}$

- second volume of $\mathrm{H}_{2}$ with unit

(1)

Example of calculation:

$5 \div 136=0.036765$

	Myrcene	Limonene
numbers of moles of hydrogen required	$0.036765 \times 3$ =0.11030	$0.036765 \times 2$ =0.07353
volume of hydrogen required	$0.11030 \times 24000$ $=2647.2 \mathrm{~cm}^{3} / 2.6472 \mathrm{dm}^{3}$	$0.07353 \times 24000$ $=1764.7 \mathrm{~cm}^{3} / 1.7647 \mathrm{dm}^{3}$

(4)

	Myrcene	Limonene
one hydrogen per terpene	$0.036765 \times 24000$ =882.36	$0.036765 \times 24000$ =882.36
total volume of hydrogen required	$882.36 \times 3$ $=2647.1 \mathrm{~cm}^{3} / 2.6471 \mathrm{dm}^{3}$	$882.36 \times 2$ $=1764.7 \mathrm{~cm}^{3} / 1.7647 \mathrm{dm}^{3}$

Final answers can be found by use of ratios of 2:3 or 3:2 so not all values will necessarily be seen

Ignore rounding errors in all steps except the final answer

Both final volumes attributed to the correct terpene with some working scores (4)

Allow TE throughout

Ignore SF

[Maximum number: 9]

This question is about ethene, $\mathrm{C}_{2} \mathrm{H}_{4}$ .

(a)

The global production of ethene is about 150 million tonnes per year.

Calculate the number of molecules in 150 million tonnes of ethene.
$\left[1\right.$ tonne $=1000 \mathrm{~kg} \quad$ Avogadro constant $\left.=6.02 \times 10^{23} \mathrm{~mol}^{-1}\right]$

[ 2 ]

(b)

Ethene is used commercially to speed up the ripening of bananas.

Ethene levels of 100 parts per million (ppm) are used in ripening rooms.
Calculate the amount, in moles, of ethene in a ripening room of volume $220 \mathrm{~m}^{3}$ at a temperature of $21^{\circ} \mathrm{C}$ and pressure of $1.01 \times 10^{5} \mathrm{~Pa}$ .

Give your answer to an appropriate number of significant figures.

\left[p V=\mathrm{n} R T \quad R=8.31 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}\right]

[ 5 ]

(c)

Ethene reacts with oxygen, $\mathrm{O}_{2}$ , in the presence of a silver catalyst, to form compound Y as the only product.

[ 2 ]

(i)

When 10.0 g of ethene reacts completely with oxygen, the mass of compound Y formed is 15.7 g.

Calculate the empirical formula of Y.
You must show your working.
[A, values: H=1.0, C=12.0, O=16.0 ]

[ 2 ]

[Maximum number: 9]

Magnesium carbonate powder reacts with hydrochloric acid.

(a)

Complete the equation for this reaction by adding state symbols.

[ 1 ]

all correct state symbols

$\mathrm{MgCO}_{3}(\mathbf{s})+2 \mathrm{HCl}(\mathbf{a q}) \rightarrow \mathrm{MgCl}_{2}(\mathbf{a q})+\mathrm{H}_{2} \mathrm{O}(\mathbf{l})+\mathrm{CO}_{2}(\mathbf{g})$

Allow capital letters Ignore extra brackets

Figure for Answer to Question (a) — Edexcel A-Level Chemistry AS

(b)

A student carried out an investigation to determine the molar volume of carbon dioxide using this apparatus.

Figure for Question (b) — Edexcel A-Level Chemistry AS

The student carried out five experiments, adding a different mass of magnesium carbonate each time. The results are shown in the table.

Table for Question (b) — Edexcel A-Level Chemistry AS

[ 6 ]

(i)

Calculate the molar volume of carbon dioxide using your answers to parts (b)(ii) and (b)(iii). Give your value to an appropriate number of significant figures and include units.

\left[\begin{array}{lll} A_{\mathrm{r}} \text { values: } & \mathrm{Mg}=24.3 & \mathrm{C}=12.0 \end{array} \mathrm{O}=16.0\right]

[ 4 ]

calculation of molar mass of magnesium carbonate (1)

- calculation of moles of magnesium carbonate

(1)

- calculation of molar volume

(1)

- answer given to 2 or 3 SF and units (1) M4 dependent on award of M3

Example of calculation:

84.3

OR expression used correctly:
$[24.3+12+(3 \times 16)]$ $46 \div 0.0021352=21543 / 2.1543 \times 10^{4}\left(\mathrm{~cm}^{3}\right)$ $=22 \mathrm{dm}^{3}\left(\mathrm{~mol}^{-1}\right) / 22000 \mathrm{~cm}^{3}\left(\mathrm{~mol}^{-1}\right)$
Or $21.5 \mathrm{dm}^{3}\left(\mathrm{~mol}^{-1}\right) / 21500 \mathrm{~cm}^{3}\left(\mathrm{~mol}^{-1}\right)$
TE on any reasonable pair of values obtained
from the candidates' graph or table provided
eg $54 \mathrm{~cm}^{3}$ and $0.215(\mathrm{~g}) \rightarrow 2.5504 \times 10^{-3}(\mathrm{~mol}) \rightarrow 21$ $200 \mathrm{~cm}^{3}$

Correct answer scores 4 marks

Final answer must not be given as a fraction to get MP4

Ignore units except for MP4

(ii)

The acid must be in excess for each experiment. Calculate the minimum concentration of hydrochloric acid needed for $30 \mathrm{~cm}^{3}$ of acid to completely react with 0.25 g of magnesium carbonate.

\mathrm{MgCO}_{3}+2 \mathrm{HCl}+\mathrm{MgCl}_{2}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2}

[ 2 ]

moles of magnesium carbonate and moles of acid in $30 \mathrm{~cm}^{3}$

(1)

- calculation of minimum concentration with units (1)

Example of calculation:
$\begin{aligned} & \mathrm{n}=0.25 / 84.3 & \mathrm{n}=0.0029655 \text { or } 0.00297 \end{aligned}$

and

1:2 stoichiometry

$\therefore 0.00593$ (moles acid)

Accept 0.00594 from 0.00297

$(0.00593 / 30) \times 1000=0.198 \mathrm{~mol} \mathrm{dm}^{-3}$

Accept answers from

0.198 to $0.200 \mathrm{~mol} \mathrm{dm}^{-3}$

Allow TE throughout e.g. $M_{\mathrm{r}}$ from 21(b)(iv) Ignore SF

Correct answer with no working scores 2

(c)

The value of molar volume calculated in (b)(iv) was lower than the student expected. Give two reasons for the value being lower than expected. Assume that the correct amounts of hydrochloric acid and magnesium carbonate were used. (2)

[ 2 ]

An answer that makes reference to any two of the following points:

- loss of gas before the bung is inserted / other named reason

(1)

- some carbon dioxide dissolved in the water

(1)

- temperature of the lab was lower than standard temperature.

(1)

Do not allow "loss of gas" unless a reason is given eg delivery tube not positioned correctly so not all goes into measuring cylinder, badly fitting bung Ignore leaks

Allow gas for carbon dioxide

Ignore higher pressure

Do not award higher temperature / lower pressure / suck-back

Ignore impurities in $\mathrm{MgCO}_{3}$

Ignore incomplete reaction

Comment: Apply the list principle ie

- 1 correct answer and 1 do not award answer scores 1

- 2 correct answers and 1 do not award answer scores 1

- 2 correct answers and 2 do not award answers scores 0

- 2 correct answers and 1 ignore scores 2

[Maximum number: 2]

Terpenes and terpenoids are groups of chemicals found in plants.
They contribute to the smell and taste of the plant, and so are used in flavourings and perfumes.

Both terpenes and terpenoids have carbon skeletons based on one or more units of the compound isoprene.

Figure for Question 4 — Edexcel A-Level Chemistry AS

isoprene
Terpenes are made up of two or more isoprene units joined together, while terpenoids have additional functional groups, often containing oxygen.

Limonene and myrcene are both terpenes composed of two isoprene units.
Menthol, linalool and citronellol are terpenoids containing an - OH group.

Show that myrcene and limonene are terpenes by comparing the molecular and/or empirical formulae of myrcene, limonene and isoprene.

myrcene

limonene

isoprene

An answer that makes reference to the following points:

- molecular formula of either myrcene, limonene or both is $\mathrm{C}_{10} \mathrm{H}_{16}$ and the molecular / empirical formula of isoprene is $\mathrm{C}_{5} \mathrm{H}_{8}$

- so the molecular formula of myrcene and limonene is twice isoprene (so they are terpenes)

OR

- molecular formula of either myrcene, limonene or both is $\mathrm{C}_{10} \mathrm{H}_{16}$ and the molecular / empirical formula of isoprene is $\mathrm{C}_{5} \mathrm{H}_{8}$

- so the empirical formula of myrcene and limonene is the same as isoprene (so they are terpenes)

[Maximum number: 2]

This question is about ethene, $\mathrm{C}_{2} \mathrm{H}_{4}$ .

The global production of ethene is about 150 million tonnes per year.

Calculate the number of molecules in 150 million tonnes of ethene.
$\left[1\right.$ tonne $=1000 \mathrm{~kg} \quad$ Avogadro constant $\left.=6.02 \times 10^{23} \mathrm{~mol}^{-1}\right]$

[Maximum number: 1]

Magnesium carbonate powder reacts with hydrochloric acid.

Complete the equation for this reaction by adding state symbols.

all correct state symbols

$\mathrm{MgCO}_{3}(\mathbf{s})+2 \mathrm{HCl}(\mathbf{a q}) \rightarrow \mathrm{MgCl}_{2}(\mathbf{a q})+\mathrm{H}_{2} \mathrm{O}(\mathbf{l})+\mathrm{CO}_{2}(\mathbf{g})$

Allow capital letters Ignore extra brackets

Figure for Answer to Question 6 — Edexcel A-Level Chemistry AS

[Maximum number: 1]

This question is about alkenes.

Bisabolenes are a group of compounds found in plants and fungi. Bisabolene molecules contain several carbon-carbon double bonds.
5.51 g of $\alpha$ -bisabolene reacted with $1873 \mathrm{~cm}^{3}$ of hydrogen gas, $\mathrm{H}_{2}$ . The reaction occured at a temperature of $150^{\circ} \mathrm{C}$ and a pressure of 152000 Pa .
$\left[M_{\mathrm{r}}\right.$ value: $\quad \alpha$ -bisabolene $\left.=204.0\right]$

Calculate the amount, in mol, of $\alpha$ -bisabolene in 5.51 g .

calculation of number of moles

Example of calculation

$5.51/204=0.027010\;(\mathrm{mol})$

Correct answer with no working scores 1

Ignore SF except 1SF

Ignore incorrect units

[Maximum number: 1]

This question is about magnesium, magnesium oxide and magnesium sulfate.

Hydrated crystals of magnesium sulfate, $\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}$ , can be made by reacting magnesium with sulfuric acid.

In an experiment, magnesium was added to $30.0 \mathrm{~cm}^{3}$ of $0.500 \mathrm{~mol} \mathrm{dm}^{-3}$ sulfuric acid.
$\left[M_{\mathrm{r}}\right.$ value: $\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}=246.4 \quad A_{\mathrm{r}}$ value: $\left.\mathrm{Mg}=24.3\right]$

Calculate the number of moles of sulfuric acid used in this experiment.

number of moles of sulfuric acid

Example of calculation
$30 \times 0.5 \div 1000=0.015 / 1.5 \times 10^{-2}(\mathrm{~mol})$

Do not award 1 SF .

(1)

[Maximum number: 1]

An organic compound contains 53.3% carbon, 11.1% hydrogen and 35.6% oxygen by mass. The molar mass of this compound is $90.0 \mathrm{~g} \mathrm{~mol}^{-1}$ .
[Data: $A_{\mathrm{r}} \mathrm{H}=1.0 \quad \mathrm{C}=12.0 \quad \mathrm{O}=16.0$ ]
What is the empirical formula of the compound?

A

$\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}$

B

$\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}_{2}$

C

$\mathrm{C}_{4} \mathrm{H}_{5} \mathrm{O}_{2}$

D

$\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O}$

[Maximum number: 1]

This question is about magnesium, magnesium oxide and magnesium sulfate.

Hydrated crystals of magnesium sulfate, $\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}$ , can be made by reacting magnesium with sulfuric acid.

In an experiment, magnesium was added to $30.0 \mathrm{~cm}^{3}$ of $0.500 \mathrm{~mol} \mathrm{dm}^{-3}$ sulfuric acid.
$\left[M_{\mathrm{r}}\right.$ value: $\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}=246.4 \quad A_{\mathrm{r}}$ value: $\left.\mathrm{Mg}=24.3\right]$

Calculate the mass of magnesium needed to react with the sulfuric acid.

mass of Mg

Example of calculation
$0.015 / 1.5 \times 10^{-2} \times 24.3=0.3645(\mathrm{~g})$

Ignore SF except 1SF

TE on (e)(i).

(1)

[Maximum number: 3]

This question is about alkenes.

Bisabolenes are a group of compounds found in plants and fungi. Bisabolene molecules contain several carbon-carbon double bonds.
5.51 g of $\alpha$ -bisabolene reacted with $1873 \mathrm{~cm}^{3}$ of hydrogen gas, $\mathrm{H}_{2}$ . The reaction occured at a temperature of $150^{\circ} \mathrm{C}$ and a pressure of 152000 Pa .
$\left[M_{\mathrm{r}}\right.$ value: $\quad \alpha$ -bisabolene $\left.=204.0\right]$

Calculate the amount, in mol, of hydrogen gas that reacted with $\alpha$ -bisabolene. Use the ideal gas equation, p V=n R T.

\left[R=8.31 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}\right]

rearrangement of ideal gas equation (1)

- conversion of temperature and volume to appropriate units

(1)

- calculation of moles of hydrogen (1)

Example of calculation
$n=\frac{pV}{RT}$

M1 may be subsumed in M3

423( K), 1873 x 10^-6( m^3)

Allow 423( K), 1873 x 10^-3(dm^3), 152(kPa)

Allow 423.15 K (which gives final answer of 0.080963)
$=\frac{(152\times10^{3})\times(1873\times10^{-6})}{8.31\times423}=0.080992\;/\;0.08099\;/\;0.0810\;/\;0.081\;(\mathrm{mol})$

Correct answer with no working scores 1

Allow TE from M2 to M3

Ignore SF except 1SF

Penalise use of 1 SF once only in (c)(i) and (c)(ii)

[Maximum number: 2]

This question is about magnesium, magnesium oxide and magnesium sulfate.

Hydrated crystals of magnesium sulfate, $\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}$ , can be made by reacting magnesium with sulfuric acid.

In an experiment, magnesium was added to $30.0 \mathrm{~cm}^{3}$ of $0.500 \mathrm{~mol} \mathrm{dm}^{-3}$ sulfuric acid.
$\left[M_{\mathrm{r}}\right.$ value: $\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}=246.4 \quad A_{\mathrm{r}}$ value: $\left.\mathrm{Mg}=24.3\right]$

The magnesium sulfate solution was allowed to crystallise.

The crystals were dried and weighed.
The mass of the hydrated crystals, $\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}$ , was 2.78 g .
Calculate the percentage yield in this experiment.

[Maximum number: 4]

Precipitation reactions can be used to determine the formulae of compounds.
A bottle has a torn label which shows that it contains a nitrate with the formula X(NO_3)_2.

Figure for Question 13 — Edexcel A-Level Chemistry AS

Procedure
- a technician dissolved a sample of 12.41 g of the nitrate in deionised water to make 100 cm^3 of solution
- the technician pipetted 5.0 cm^3 of 1.50 mol dm^-3 potassium iodide into each of a series of test tubes
- each test tube then had a volume of the nitrate solution added to it as shown in the table
- a cloudy yellow solution formed, and the precipitate was allowed to settle
- the height of the precipitate was then measured.

The equation for the reaction is

\mathrm{X}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+2 \mathrm{KI}(\mathrm{aq}) \rightarrow \mathrm{XI}_{2}(\mathrm{~s})+2 \mathrm{KNO}_{3}(\mathrm{aq})

The results of the experiment are shown.

Table for Question 13 — Edexcel A-Level Chemistry AS

Identify X by using your answers to (b)(i), (b)(ii) and (b)(iii) to determine the M_r of the metal nitrate. You must show all your working.

[Maximum number: 2]

Magnesium carbonate powder reacts with hydrochloric acid.

The value of molar volume calculated in (b)(iv) was lower than the student expected. Give two reasons for the value being lower than expected. Assume that the correct amounts of hydrochloric acid and magnesium carbonate were used. (2)

An answer that makes reference to any two of the following points:

- loss of gas before the bung is inserted / other named reason

(1)

- some carbon dioxide dissolved in the water

(1)

- temperature of the lab was lower than standard temperature.

(1)

Do not allow "loss of gas" unless a reason is given eg delivery tube not positioned correctly so not all goes into measuring cylinder, badly fitting bung Ignore leaks

Allow gas for carbon dioxide

Ignore higher pressure

Do not award higher temperature / lower pressure / suck-back

Ignore impurities in $\mathrm{MgCO}_{3}$

Ignore incomplete reaction

Comment: Apply the list principle ie

- 1 correct answer and 1 do not award answer scores 1

- 2 correct answers and 1 do not award answer scores 1

- 2 correct answers and 2 do not award answers scores 0

- 2 correct answers and 1 ignore scores 2

[Maximum number: 2]

This question is about magnesium, magnesium oxide and magnesium sulfate.

Magnesium sulfate can be made by reacting magnesium with dilute sulfuric acid.

Give two observations you would make when the reaction is taking place.

Edexcel A-Level Chemistry AS 1 Formulae Equations and Amount of Substance Questions

Exam points

Covered syllabus points

Covered syllabus points

Question 1

Question (a)

Question (b)

Question 2

Question (a)

Question (b)

Question (c)

Question (i)

Question 3

Question (a)

Question (b)

Question (i)

Question (ii)

Question (c)

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question 12

Question 13

Question 14

Question 15