Question
Which statement shows that a liquid is pure water?
A It boils at $100^{\circ} \mathrm{C}$.
B It has a pH value of 7 .
C It turns blue cobalt(II) chloride pink.
D It turns white copper(II) sulfate blue.
▶️Answer/Explanation
Ans:A
If a liquid boils at exactly 100 degrees Celsius under standard atmospheric pressure (1 atmosphere or 101.3 kPa), then it is pure water. Boiling point is a characteristic property of a substance, and for water at sea level, the boiling point is 100 degrees Celsius (212 degrees Fahrenheit).
Question
The diagrams show some uses of water in the home.
For which uses is it important for the water to have been treated?
A 1 only B 2 only C 3 only D 1, 2 and 3
▶️Answer/Explanation
Ans: A
For cooking, treated water must be used.
Question
Which substances do not produce water as a product when they are reacted together?
A calcium hydroxide and ammonium chloride
B calcium carbonate and dilute hydrochloric acid
C copper(II) oxide and dilute nitric acid
D zinc and dilute sulfuric acid
▶️Answer/Explanation
Ans: D
When zinc reacts with dilute sulfuric acid, it does not produce water as a product of the reaction.
In this reaction, zinc (Zn) reacts with dilute sulfuric acid to form zinc sulfate in aqueous solution, and hydrogen gas is evolved as a product.
Question
Water is treated at a waterworks to make it fit to drink.
What is present in the water when it leaves the waterworks?
A bacteria only
B bacteria and insoluble substances
C chlorine compounds only
D chlorine compounds and soluble substances
▶️Answer/Explanation
Ans: D
Water treatment facilities often add chlorine or other disinfectants to kill harmful bacteria and microorganisms, ensuring the water remains safe during distribution. After treatment, some amount of chlorine or other disinfectants may remain in the water to provide ongoing protection against potential contamination as the water travels through the distribution system.
Treated water may contain essential minerals such as calcium, magnesium, potassium, and sodium, which can be beneficial for health.
Question
Which test is used to show that a sample of water is pure?
A Evaporate the water to see if any solids remain.
B Heat the water to check its boiling point.
C Test with anhydrous cobalt(II) chloride.
D Use universal indicator paper to check its pH.
▶️Answer/Explanation
Ans: B
If a liquid boils at exactly 100 degrees Celsius under standard atmospheric pressure (1 atmosphere or 101.3 kPa), then it is likely pure water. Boiling point is a characteristic property of a substance, and for water at sea level, the boiling point is 100 degrees Celsius (212 degrees Fahrenheit).