Your answers are all correct.

Question 1:
Colour of copper(II) sulphate crystals are indeed due to the Water of Crystallization.

Question 2:
Based on the Table of Solubility of Salts (which is required to memorise and know well for O Level Chemistry), Potassium Nitrate is the only salt in the list to be soluble in water, and can be crystallized from its aqueous solutions.

Question 3:
Many students got this question wrong in my chemistry workshops and bootcamps when i tested them.

Many chose Copper Hydroxide as the answer which is incorrect. Just because Copper is one of the least reactive metals in the Metal & Reactivity Series, they thought Copper(II) Hydroxide will be unreactive. This is NOT true. Copper(II) Hydroxide does has the properties just like any other alkalis.

The clue for this question comes from “does not give a good yield of the salt”.
It hints that the salt will not form properly due to some reasons. Based on Table of Solubility of Salts, Calcium Sulphate that is formed between Sulphuric Acid + Calcium Hydroxide is INSOLUBLE in Water. As such, it will form a layer around the calcium hydroxide and prevents reaction from continuing smoothly. The same does not happen for other salts given, which are soluble in water.

Cheers
Sean

The first question is quite alright. Hopefully everyone knows that the water of crystallisation (or simply water molecules) is what gives the copper(II) sulphate it’s colour.

Potassium nitrate is the only one which is soluble in water. They say aqueous solution, hence I gather they’re asking us which one of those salts are soluble in water.

Question three requires us to spot the odd one out. In this case, it’s calcium hydroxide. When Calcium hydroxide reacts with sulphuric acid, it produces a calcium sulphate, which is insoluble, and hence will form a layer around the calcium hydroxide and stop the reaction from continuing. The same doesn’t happen for the other salts given in the question.