Exam Questions

Question 1

Phosphorus (III) chloride molecules are pyramidal with a bond angle less than 109.5. Explain why. (2)

Answer 1

Pyramidal because there are 3 bonding pairs and one lone pair of electrons on P
Bond angle because lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion

Question 2

Calcium Nitrate decomposes in a similar way to magnesium nitrate, but needs a higher temperature. Explain in terms of the charge and size of the cations. (3)

Answer 2

Ca2+ has larger ionic radius
So Ca2+ causes less polarisation
Nitrate ion electron cloud polarised

Question 3

Explain why boiling temperatures increase from chlorine to iodine. (2)

Answer 3

Down the group, number of electrons increases

So strength of London forces increases and more energy needed to separate the molecules

Question 4

Explain why zinc ions are colourless (2)

Answer 4

Zinc ions have a full 3d subshell

So electrons cannot move between d orbitals/cannot be promoted

Question 5

Explain why the first ionisation energy of magnesium is higher than that of sodium (3)

Answer 5

Magnesium has more protons than Sodium, greater effective nuclear charge
Shielding in Magnesium the same as in Sodium
Force of attraction between nucleus and outer electron is greater in Mg

Question 6

Explain why different alkanes in crude oil can be separated by fractional distillation (2)

Answer 6

Different alkanes have different boiling temperature

Because of different chain length/strength of intermolecular forces

Question 7

Describe how reactions happen in catalytic converters (3)

Answer 7

Adsorption to catalytic surface
Weakenign of bonds on catalytic surface
Desorption of products

Question 8

Give the steps to show have 2,4-DNPH can be used to distinguish between phenylethanone and phenylethanal (4)

Answer 8

Formation of yellow/orange precipitate
Filter then recrystallise products
Determination of melting temperature
Comparison and identification from use of database