Water

Water is the most abundant compound on Earth.

Heat from the Sun causes evaporation only from oceans, seas, and lakes.

Tap water boils exactly at 100°C.

The water cycle is driven by wind currents.

Distilled water is used in labs because it is impure.

Adding an unknown liquid to anhydrous copper(II) sulfate can test for the presence of water.

Water may be electrolysed when acidified with dilute sulfuric acid, resulting in a 1:1 ratio of hydrogen to oxygen gas.

Hydrogen bonds in water are stronger than covalent bonds.

Water decreases in density when it freezes.

Pure water is an acidic liquid.

Water is an excellent solvent for ionic substances like sodium chloride.

Water has a lower specific heat capacity compared to most other liquids.

Boiling point of water is unusually high for a molecule of its relatively low molecular mass because of hydrogen bonding.

The water used in industry and homes is returned to rivers or seas without any treatment.

The majority of the Earth\’s surface is covered by water.

The human skeleton contains more water by percentage than the kidneys.

The sun is not involved in the water cycle on Earth.

Clouds form through the condensation of water vapor.

Rainwater directly enters the sea without going through rivers or lakes.

Pure water has a fixed boiling point of 100°C at 1 atmosphere pressure.

Tap water boils at exactly 100°C because it is pure.

Distilled water is impure and contains many dissolved substances.

Anhydrous copper(II) sulfate turns from white to blue if it comes in contact with water.

When water is electrolyzed, the gas volume ratio at the cathode to anode is 1:2.

Water is not a chemical reactant in industrial processes.

Transpiration is a process where water evaporates from the surface of leaves.

Reservoirs are natural bodies of water where rainwater is collected before it reaches the ocean.

Water is a poor solvent and does not dissolve many substances.

Acidified water with dilute sulfuric acid cannot be electrolyzed.

Water must be purified before it is suitable for use in the home.
Which processes are used to remove solid impurities and bacteria?

\[
\begin{array}{|c|c|c|}
\hline & \begin{array}{c}
\text { to remove } \\
\text { solid impurities }
\end{array} & \begin{array}{c}
\text { to remove } \\
\text { bacteria }
\end{array} \\
\hline \text { A } & \text { chlorination } & \text { chlorination } \\
\text { B } & \text { chlorination } & \text { filtration } \\
\text { C } & \text { filtration } & \text { chlorination } \\
\text { D } & \text { filtration } & \text { filtration } \\
\hline
\end{array}
\]

The diagram shows stages in the purification of water. Which stage uses chlorine?

Which statements about water are correct?

1. Water is treated with chlorine to kill bacteria.
2. Household water may contain salts in solution.
3. Water is used in industry for cooling.
4. Water for household use is filtered to remove soluble impurities.

Water from a reservoir flows to the water works where purification processes 1 takes place followed by process 2. What are purification processes 1 and 2 ?

\[
\begin{array}{|c|c|c|}
\hline & \begin{array}{c}
\text { purification } \\
\text { process } 1
\end{array} & \begin{array}{c}
\text { purification } \\
\text { process } 2
\end{array} \\
\hline \text { A } & \text { chlorination } & \text { filtration } \\
\text { B } & \text { filtration } & \text { chlorination } \\
\text { C } & \text { fractional distillation } & \text { filtration } \\
\text { D } & \text { filtration } & \text { fractional distillation } \\
\hline
\end{array}
\]

Some uses of water are listed.

1. for drinking
2. in chemical reactions
3. in swimming pools
4. in washing

For which uses is it necessary to chlorinate the water?

Air containing an acidic impurity was neutralised by passing it through a column containing substance X.

What is substance X ?

Water has been contaminated with sea-water.
Which substances can be removed by chlorination and filtration?

Water is treated at a water works to make it fit to drink.
What is present in the water when it leaves the waterworks?

Which method of purification would produce water most suitable for drinking?

The diagram shows stages in producing drinking water.
In which tank is chlorine added to the water?

Which statement shows that a liquid is pure water?

Which substances can be used to detect the presence of water?

1. cobalt(II) chloride
2. copper(II) sulfate
3. litmus
4. methyl orange

What are possible effects of an inadequate water supply during a drought?

1. crop failure
2. wastage of water
3. human disease
4. death of farm animals