Edexcel IAL Chemistry Unit 1 Structure, bonding and organic chemistry

Use the Unit 1 question bank to connect particle and bonding models with equations, mole calculations, organic representations and evidence from chemical data.

Covered syllabus points

Topic 1: Formulae, Equations and Amount of Substance Topic 2: Atomic Structure and the Periodic Table Topic 3: Bonding and Structure Topic 4: Introductory Organic Chemistry and Alkanes Topic 5: Alkenes

[Maximum number: 9]

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 Unit 1: Structure, Bonding and Introduction to Organic Chemistry 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)

Give the IUPAC name for isoprene.

[ 1 ]

(b)

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)

(c)

Both myrcene and limonene can be completely hydrogenated by reaction with hydrogen.
State the conditions required for hydrogenation of alkenes.

[ 1 ]

(d)

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)

\multirow{4{*}{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

$0.11030 \times 24000$ $=2647.2 \mathrm{~cm}^{3} / 2.6472 \mathrm{dm}^{3}$ $0.07353 \times 24000$ $=1764.7 \mathrm{~cm}^{3} / 1.7647 \mathrm{dm}^{3}$

\end{tabular}
\end{tabular}}}

(4)

\multirow{3{*}{& Myrcene & Limonene

one hydrogen per

terpene

$0.036765 \times 24000$

=882.36

$0.036765 \times 24000$

=882.36

total volume of

hydrogen required

$882.36 \times 3$ $=2647.1 \mathrm{~cm}^{3} / 2.6471 \mathrm{dm}^{3}$ $882.36 \times 2$ $=1764.7 \mathrm{~cm}^{3} / 1.7647 \mathrm{dm}^{3}$

\end{tabular}}}

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

(e)

Give the IUPAC name of the product formed by complete hydrogenation of myrcene.

[ 1 ]

[Maximum number: 1]

Which statement about subatomic particles is correct?

neutral atoms always contain the same number of protons and electrons

neutral atoms always contain the same number of protons and neutrons

electrons have a relative mass of 1 and a charge of -1

protons have a relative mass of 1 and no charge

[Maximum number: 20]

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

(a)

A sample of magnesium contains three isotopes and has a relative atomic mass of 24.32.
The table gives the relative abundances of two of these isotopes.

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

[ 6 ]

(i)

Calculate the relative abundance and hence the mass number of the third isotope.
Give your answer to the appropriate number of significant figures.
You must show all your working.

[ 4 ]

An answer that makes reference to the following points:

- calculation of the \% abundance of the third isotope

(1)

- substitute equation

(1)

- calculation of the mass of the $3^{\text {rd }}$ isotope

(1)

- answer to 2 SF only

(1)

Example of calculation

100-78.99-10.00=11.01(%)

100-78.99-10.00 = 11.01(\%)

$24.32=\frac{(24 \times 78.99)+(25 \times 10)+(y \times 11.01)}{100}$ $\mathrm{y}=\frac{2432-(24 \times 78.99)-(25 \times 10)}{11.01}$

y=25.998

(4)

(ii)

State one similarity and one difference between these isotopes.

[ 1 ]

(iii)

State which of these isotopes would be deflected most in a mass spectrometer. Justify your answer.

[ 1 ]

An answer that makes reference to the following point:

- ${ }^{24} \mathrm{Mg}$ and lowest mass or lowest m / z ratio (so deflected more by the magnetic field)

Allow ${ }^{24} \mathrm{Mg}$ is lightest Allow ${ }^{24} \mathrm{Mg}^{+}$

Ignore just the lowest mass

(1)

(b)

Magnesium oxide and magnesium sulfate are ionic compounds.

[ 4 ]

(i)

Draw a dot-and-cross diagram to show the bonding in magnesium oxide, MgO .
Show outer electrons only.

[ 2 ]

(ii)

The melting temperatures of magnesium oxide and magnesium sulfate are $2852^{\circ} \mathrm{C}$ and $1124^{\circ} \mathrm{C}$ respectively.

Explain why the melting temperature of magnesium oxide is significantly higher than that of magnesium sulfate.

[ 2 ]

An answer that makes reference to the following points:

- oxide/ $\mathrm{O}^{2-}$ smaller than sulfate/ $\mathrm{SO}_{4}{ }^{2-}$

- stronger (electrostatic) attraction between the ( $\mathrm{Mg}^{2+}$ and $\mathrm{O}^{2-}$ ) ions

Allow just the oxide is smaller or vice versa Do not award comparison with sulfur or sulfide

Allow stronger ionic bond

Allow more energy required to break the ionic bond

Allow reverse argument Ignore reference to lattice energy Ignore reference to distortion/polarisation Any reference to intermolecular forces /covalent bond/molecular structure score 0

(2)

(c)

The table gives some data about the electrical conductivity of magnesium and magnesium oxide.

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

Explain the similarities and differences in the electrical conductivity of the two substances.

[ 2 ]

(d)

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

[ 4 ]

(i)

Write an equation for the reaction that occurs.

Include state symbols in your answer.

[ 2 ]

Example of equation
$\begin{aligned} \mathrm{Mg}(\mathrm{~s}) +\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \longrightarrow \mathrm{MgSO}_{4}(\mathrm{aq})+\mathrm{H}_{2}(\mathrm{~g}) \bullet \text { correct balanced equation } \bullet \text { correct state symbols } \end{aligned}$

(1)

(1)

$\mathrm{Mg}(\mathrm{~s})+2 \mathrm{H}^{+}(\mathrm{aq}) \longrightarrow \mathrm{Mg}^{2+}(\mathrm{aq})+\mathrm{H}_{2}(\mathrm{~g})$

Allow multiples

Allow ionic equation

M2 dependent on M1 or having the correct species in an unbalanced equation

(2)

(ii)

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

[ 2 ]

(e)

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: $\left.\mathrm{Mg}=24.3\right]$

[ 4 ]

(i)

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

[ 1 ]

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)

(ii)

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

[ 1 ]

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)

(iii)

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.

[ 2 ]

[Maximum number: 1]

When carrying out chemical experiments, the hazards and risks must be considered.
For a given chemical

the hazard is fixed but the risk varies

the hazard varies but the risk is fixed

both hazard and risk are fixed

both hazard and risk vary

All question bank results loaded

Covered syllabus points

Unit 1: Structure, Bonding and Introduction to Organic Chemistry question 1

Question (a)

Question (b)

Question (c)

Question (d)

Question (e)

Unit 1: Structure, Bonding and Introduction to Organic Chemistry question 2

Unit 1: Structure, Bonding and Introduction to Organic Chemistry question 3

Question (a)

Question (i)

Question (ii)

Question (iii)

Question (b)

Question (i)

Question (ii)

Question (c)

Question (d)

Question (i)

Question (ii)

Question (e)

Question (i)

Question (ii)

Question (iii)

Unit 1: Structure, Bonding and Introduction to Organic Chemistry question 4