Jan 2023

Question 1

1.3. Give a further reagent that the student could add to confirm the identity of the bromide ion in the precipitate. State what the student would observe. (2)

Answer 1

(1) add concentrated ammonia

(2) precipitate disappears / colourless solution forms

Question 2

4.4. State 2 ways that the student could make sure that the mass of the sodium carbonate in the volumetric flask is known exactly (titration). (2)

Answer 2

(1) weigh by difference

(2) transfer the washings into the volumetric flask

Question 3

4.5. In a titration, the pipette and burette are rinsed before use. State why they’re rinsed before use. (1)

Answer 3

to remove other solutions (that may be present from previous
experiments) or to stop contamination (from previous solutions)

Question 4

5.6. Suggest why the data book value for the bond enthalpy of the C–H bond is different from the calculated value in 5.5. (1)

Answer 4

(bond enthalpies are) averages / mean values (measured over several compounds)

Question 5

6.2. Explain, in terms of structure and bonding, why the melting point of magnesium is higher than the melting point of sodium. (2)

Answer 5

(1) Mg has smaller ions or Mg ions have bigger charge density or Mg2+ has a higher charge than Na+ or Mg atoms are smaller than Na atoms
(2) stronger attraction with delocalised / free / sea of electrons

Question 6

6.8. State the meaning of electronegativity (1)

Answer 6

power of an atom to attract electron density / pair of electrons / two electrons towards itself in a covalent bond