Jan 2022

Question 1

1.2. Explain why the first ionisation energy of sulfur is less than the first ionisation energy of phosphorus. (2)

Answer 1

(1) (outer) electrons in (3)p orbital or sub-shell begin to pair

(2) (paired electrons) repel

Question 2

2.3. Explain how VDW forces arise. (3)

Answer 2

(1) electron movement or temporary dipole in first molecule

(2) induces / creates a (temporary) dipole in another molecule or induces δ+ and δ- in another molecule

(3) δ+ in one molecule attracts δ- in different / adjacent molecule

Question 3

2.4. Explain how a lone pair of electrons in a molecule of NF3 affects the bond angle in the molecule. (2)

Answer 3

(1) lone pairs repel more than bonding pairs

(2) bond angle will be reduced (from that in a regular shape)

Question 4

4.3. Suggest 2 reasons why the value for the enthalpy of combustion of propan-1-ol calculated in a Q is different from the value in the book (2)

Answer 4

(1) bond enthalpies are averages / mean values

(2) bond enthalpy calculations are for gaseous substances

Question 5

5.4. A few drops of aqueous bromine are added to a test tube that contains some sodium iodide solution. State the colour change observed in the test tube. (1)

Answer 5

colourless (NaI solution) turns to a brown (solution) / black solid

Question 6

6.2. The most abundant isotope of argon has Mr = 40.
The most abundant isotope of potassium has Mr = 39.
Justify why argon is placed before potassium in the Periodic Table. (2)

Answer 6

(1) periodic table is in order of atomic number / proton number

(2) K has Z = 19 but Ar has Z = 18 or K has one more proton than Ar

Question 7

7.3. Describe a test-tube reaction to show that a solution of ammonium chloride contains ammonium ions. (2)

Answer 7

(1) add sodium hydroxide or potassium hydroxide (and warm)
(2) ammonia / gas evolved which turns (red) litmus (paper) blue