Jan 2020

Question 1

2.2. A mixture contains solid sodium carbonate and solid sodium sulfate. Describe how a pure sample of solid sodium sulfate can be obtained from the mixture. (3)

Answer 1

(1) Add sulfuric acid (to react with the sodium carbonate to form sodium sulfate and water and CO2)
(2) (add the acid) until effervescence ceases / fizzing stops
(3) Evaporate (to dryness)

Question 2

6.2. Explain, in terms of structure and bonding, why the melting point of silicon is much higher than the melting point of phosphorus. (4)

Answer 2

(1) Silicon in macromolecular or giant covalent or giant atomic
(2) silicon contains many covalent bonds
(3) phosphorus has vdw forces (dispersion forces etc) between molecules
(4) Covalent bonds require much more energy to break than vdw / covalent bonds are stronger than vdw forces

Question 3

6.4. Explain why the first ionisation energy of sulfur is lower than that of phosphorus (2)

Answer 3

(1) Electrons are paired in (3)p orbital in S
(2) Paired electrons repel (so less energy needed to remove)

Question 4

7.5. Explain why chlorine is a stronger oxidising agent than Bromine. (2)

Answer 4

(1) Chlorine (atom/molecule) is smaller OR chlorine has less electron shells OR chlorine has less shielding
(2) Attraction to (outer/gained) electron in chlorine is stronger OR (gained / outer) electron is more tightly held