AQA A Level Chemistry Paper 3 Markscheme
2024 [VERIFIED]
Define the term relative atomic mass (2 marks). - Correct Answer--.1. The average mass of an
atom of an element
(average mass of all isotopes of an element)
2. Compared to 1/12th the mass of an atom of carbon-12
Describe how molecules are ionised using electrospray ionisation (4 marks). - Correct Answer--
1. Sample dissolved (in a volatile solvent)
(allow named solvent eg water or methanol)
2. (injected through) a needle or nozzle or capillary and at high voltage/4000 volts or high
potential
(allow needle is positively charged)
3. Gains a proton / H+
4. X + H+ → XH+
Outline how the TOF mass spectrometer works (4 marks). - Correct Answer--1. Positive ions are
accelerated by an electric field
(allow (ions) accelerated to a negative plate)
2. To a constant kinetic energy
3. Ions create a current when hitting the detector
4. The size of the current is proportional to the abundance of ions hitting the plate and gaining
an electron
The student rinses the burette with deionised water before filling with
sodium hydroxide solution.
State and explain the effect, if any, that this rinsing will have on the value of
, the titre (2 marks). - Correct Answer--1. Titre value would increase / larger value
2. Because the sodium hydroxide solution would be more dilute
The student used a wash bottle containing deionised water when
approaching the end-point to rinse the inside of the conical flask.
Explain why this improved the accuracy of the titration (1 mark). - Correct Answer--1. Idea that
it ensures all ethanedioic acid / acid / sodium hydroxide / alkali / reactants are in the mixture /
solution / reaction
OR
the idea that some of the ethanedioic acid / acid / sodium hydroxide / alkali / reactants would
be on the sides of the flask
Explain why pentan-2-ol has a higher boiling point than pent-1-ene (3 marks). - Correct Answer--
1. Pentan-2-ol has stronger intermolecular forces
2. Pent-1-ene has van der Waals' forces (only)
3. Pentan-2-ol (also) has hydrogen bonds
Explain why a fluoride ion is larger than a sodium ion (2 marks). - Correct Answer--1. Fluoride
ion has (two) fewer protons/lower nuclear charge
2. Weaker attraction between nucleus and (outer) electrons
Explain, in terms of structure and bonding, why the melting point of sodium fluoride is high (2
marks). - Correct Answer--1. (Electrostatic) forces of attraction between oppositely charged
ions/Na+ and F-
2. Lots of energy needed to overcome/break forces
Explain how the lone pairs of electrons on the oxygen atom influence the
2024 [VERIFIED]
Define the term relative atomic mass (2 marks). - Correct Answer--.1. The average mass of an
atom of an element
(average mass of all isotopes of an element)
2. Compared to 1/12th the mass of an atom of carbon-12
Describe how molecules are ionised using electrospray ionisation (4 marks). - Correct Answer--
1. Sample dissolved (in a volatile solvent)
(allow named solvent eg water or methanol)
2. (injected through) a needle or nozzle or capillary and at high voltage/4000 volts or high
potential
(allow needle is positively charged)
3. Gains a proton / H+
4. X + H+ → XH+
Outline how the TOF mass spectrometer works (4 marks). - Correct Answer--1. Positive ions are
accelerated by an electric field
(allow (ions) accelerated to a negative plate)
2. To a constant kinetic energy
3. Ions create a current when hitting the detector
4. The size of the current is proportional to the abundance of ions hitting the plate and gaining
an electron
The student rinses the burette with deionised water before filling with
sodium hydroxide solution.
State and explain the effect, if any, that this rinsing will have on the value of
, the titre (2 marks). - Correct Answer--1. Titre value would increase / larger value
2. Because the sodium hydroxide solution would be more dilute
The student used a wash bottle containing deionised water when
approaching the end-point to rinse the inside of the conical flask.
Explain why this improved the accuracy of the titration (1 mark). - Correct Answer--1. Idea that
it ensures all ethanedioic acid / acid / sodium hydroxide / alkali / reactants are in the mixture /
solution / reaction
OR
the idea that some of the ethanedioic acid / acid / sodium hydroxide / alkali / reactants would
be on the sides of the flask
Explain why pentan-2-ol has a higher boiling point than pent-1-ene (3 marks). - Correct Answer--
1. Pentan-2-ol has stronger intermolecular forces
2. Pent-1-ene has van der Waals' forces (only)
3. Pentan-2-ol (also) has hydrogen bonds
Explain why a fluoride ion is larger than a sodium ion (2 marks). - Correct Answer--1. Fluoride
ion has (two) fewer protons/lower nuclear charge
2. Weaker attraction between nucleus and (outer) electrons
Explain, in terms of structure and bonding, why the melting point of sodium fluoride is high (2
marks). - Correct Answer--1. (Electrostatic) forces of attraction between oppositely charged
ions/Na+ and F-
2. Lots of energy needed to overcome/break forces
Explain how the lone pairs of electrons on the oxygen atom influence the
