Past Paper Questions and SQA Answers

Question 1

2024 1(b)
The melting points of phosphorus and nitrogen are shown.

Nitrogen -210
Phosphorus 44

Explain why the melting point of phosphorus, P4, is much higher than that of nitrogen, N2.

In your answer you should refer to the intermolecular forces involved.

Answer 1

Stronger intermolecular/Van der
Waals forces between phosphorus
compared with nitrogen. (1 mark)

London dispersion forces/LDFs are
the intermolecular forces present.
(1 mark)

There are more electrons in
phosphorus/P4 compared to
nitrogen/N2. (1 mark)

Any mention of breaking
covalent/ionic/metallic bonds is
cancelling.

Question 2

2024 2(c)
The metal oxides react with silicon dioxide, SiO2, to form
less harmful by-products.
Silicon dioxide has a melting point of 1713 °C.
Explain fully, in terms of structure and bonding, why silicon dioxide has a high
melting point

Answer 2

Silicon dioxide is a covalent network
(1 mark)

(Strong) covalent bonds are broken
(1 mark)

‘Covalent lattice’ is acceptable, but
lattice on its own is not.
Naming silicon as the covalent
network is cancelling for first mark.
Covalent network molecule is
cancelling for first mark.
A diagram of a molecule is
cancelling for the first mark.

Question 3

2024 7(b)i.B
Describe how a pipette should be prepared and used to accurately
measure the sample of seawater.

Answer 3

Rinse with
seawater/sample/solution
(1 mark)
Fill above the mark and allow liquid
to drop down to the mark (and read
from the bottom of the meniscus)
(1 mark)
OR
Fill to mark, read from the bottom
of the meniscus (1 mark)

Rinse with water is not accepted.

Question 4

2024 7(c)
Some micro-organisms living in seawater convert chloride ions to
chloromethane. The chloromethane then evaporates.
H
|
H —– C _____ H
/\
Cl
Explain fully why chloromethane has a lower boiling point than water.
In your answer you should refer to the intermolecular forces involved.

Answer 4

Chloromethane has permanent
dipole to permanent dipole
interactions whereas water has
hydrogen bonding. (1 mark)

Hydrogen bonding is stronger than
permanent dipole to permanent
dipole interactions. (1 mark)

Question 5

2024 9(a)ii
Titanium chloride is a liquid at room temperature.
Suggest the type of bonding and structure present in titanium chloride.

Answer 5

Covalent molecular or discrete covalent molecular

Question 6

2023 1(a)iiiA
The table shows four ionisation energies of sodium.
Ionisation energy (kJ mol−
)
First 496
Second 4562
Third 6910
Fourth 9543

(A) Explain fully the large increase between the first and second
ionisation energies of sodium.

Answer 6

Second ionisation energy involves
removal of an electron from an
electron shell that is inner/
full(whole)/(more) stable/closer to
the nucleus.
OR
Second electron is removed from an
electron shell that is inner/
full(whole)/(more) stable/closer to
the nucleus. (1 mark)

The second electron is less
screened/the second electron shell
is less screened.
OR
The second electron is more strongly
attracted to/pulled towards the
nucleus. (1 mark)

Correct statements made about the
1st ionisation energy/electron can
also be credited.
Stating that the 2nd electron requires
more energy than the 1st electron is
not sufficient on its own.
Shielding is acceptable in place of
screening.
Increased attraction of the electron
for the nucleus would be considered
cancelling.

Question 7

2023 1(b)ii
Explain fully why electronegativity decreases going down a group.

Answer 7

(More shells so) increased
screening/more screening. (1 mark)

(Covalent radius increases/atom size
increases/more shells so) attraction
of the nucleus/protons for the
(outer/shared) electron(s)
decreases. (1 mark)

Shielding is acceptable in place of
screening.
Increased attraction of the electron
for the nucleus would be considered
cancelling.

Question 8

2023 2(a)i
Explain fully why the boiling points of the group 4 hydrides increase
going down the group.
In your answer you should refer to the intermolecular forces involved

Answer 8

(Intermolecular/van der Waals)
forces increase (going down the
group). (1 mark)

LDFs are the forces (broken between
the molecules). (1 mark)

The more electrons the stronger the
LDFs. (1 mark)

Question 9

2023 2(b)iii
The table shows the melting points of silicon hydride, SiH4, and silicon
oxide, SiO2.
Melting point (°C)
SiH4 -185
SiO2 1710
Explain fully why silicon oxide has a much higher melting point than
silicon hydride.

Answer 9

In SiO2 covalent bonds are broken.
(1 mark)

In SiH4 Van der
Waals/LDFs/intermolecular forces
are broken. (1 mark)

Covalent bonds need more energy to
break than van der Waals/LDFs/
intermolecular forces.
OR
Covalent bonds are stronger than
van der Waals/LDFs/intermolecular
forces. (1 mark)