Water Sources, Properties, Contamination and Purification

Question 1

Which of the following is considered the purest natural form of water?

Accepted Answer

Rainwater

Question 2

What is the molecular shape of a water molecule due to the repulsion between lone pairs and bonding pairs?

Accepted Answer

Bent or V-shaped

Question 3

What is the approximate bond angle between the two O-H bonds in a water molecule?

Accepted Answer

$104.5^\circ$

Question 4

Why is the water molecule polar?

Accepted Answer

Oxygen is more electronegative than hydrogen, creating partial charges.

Question 5

Based on its electronic configuration of 2, 6, how many electrons does an oxygen atom need to achieve a stable octet configuration?

Accepted Answer

2

Question 6

At what temperature does water reach its maximum density of $1\text{ g/cm}^3$?

Accepted Answer

$4\ ^\circ\text{C}$

Question 7

Why is water often referred to as the 'universal solvent'?

Accepted Answer

Its high polarity allows it to dissolve many ionic and polar covalent compounds.

Question 8

What are the products when sodium metal reacts with water?

Accepted Answer

Sodium hydroxide and hydrogen gas

Question 9

What is formed when a non-metallic (acidic) oxide like $\text{SO}_3$ reacts with water?

Accepted Answer

An acid

Question 10

What is the chemical name for the hydrate $\text{CuSO}_4\cdot5\text{H}_2\text{O}$?

Accepted Answer

Copper(II) sulphate pentahydrate

Question 11

How does the boiling point of impure water compare to that of pure water at standard pressure?

Accepted Answer

Impure water usually boils at a temperature slightly above $100\ ^\circ\text{C}$.

Question 12

What effect do impurities have on the freezing point of water?

Accepted Answer

They lower the freezing point below $0\ ^\circ\text{C}$.

Question 13

Which substance is commonly added as a coagulant during the sedimentation process to help small suspended particles clump together?

Accepted Answer

Alum (aluminium sulphate)

Question 14

What is the primary purpose of adding chlorine to water during purification?

Accepted Answer

To disinfect the water by killing bacteria and viruses

Question 15

Which water purification method involves boiling water to produce steam and then cooling it back into liquid to remove dissolved solids?

Accepted Answer

Distillation

Question 16

What laboratory process is depicted in this diagram?

Accepted Answer

Filtration

Question 17

Which purification method is shown in this laboratory setup?

Accepted Answer

Distillation

Question 18

In a filtration experiment, what is the term used for the solid particles that are retained on the filter paper?

Accepted Answer

Residue

Question 19

How many lone pairs of electrons remain on the oxygen atom in a water molecule?

Accepted Answer

2

Question 20

Which human-made contaminant from agricultural run-off leads to excessive algal growth (eutrophication) in water bodies?

Accepted Answer

Fertilisers containing nutrients

Strong work.