Worksheet 10.1 - 10.3 Answers

10.1     Acids and alkalis in daily life

II.   Fill in the blanks:

1.     Acids

Ø   In our daily life, there are many foods, drinks and flavourings that taste sour. It is because they contain (1) acids.

²  Yoghurt contains (2) lactic acid.

²  Lemons contain (3) citric acid

²  Vinegar contains (4) ethanoic acid.

Ø   Many household cleaners and personal care products also contain acids.

²  Toilet bowl cleaners contain (5) hydrochloric acid.

2.     Alkalis

Ø   Alkalis are the chemical opposite of (6)acids . They generally taste (7) bitter, and feel (8) soapy or slippery.

Ø   Alkalis are also commonly found in many household cleaners.

²  Glass cleaners contain (9) ammonia.

²  Drain and oven cleaners usually contain (10) sodium hydroxide or (11) potassium hydroxide.

10.2            Acids and alkalis in the laboratory

II.   Fill in the blanks:

1.     Acids and alkalis in the laboratory

Ø   Acids and alkalis are commonly used chemicals in the laboratory. Below are some common examples:

Common acids in the laboratory	Common alkalis in the laboratory
·  Hydrochloric acid ·  (1) Sulphuric aicd ·  (2) Nitric acid	·  Sodium hydroxide solution ·  Potassium hydroxide solution ·  (3) Calcium hydroxide ·  (4) Ammonia solution

2.     Safety precautions when handling acids and alkalis

Ø   Many acids and alkalis are either irritant or (5)corrosive.

Ø   Therefore, we should follow the (6) safety precautions below when handling acids and alkalis in the laboratory.

10.2            Acid-alkali indicators

II.   Fill in the blanks:

1.     Natural acid-alkali indicators

Ø   An acid-alkali (1) indicator shows different colours in acids and alkalis. It can be used to distinguish acids from alkalis.

Ø   Some deeply coloured plants show different colours in acids and alkalis. They can be used to make (2) natural acid-alkali indicators.

2.     Litmus paper

Ø   Litmus is a common acid-alkali indicator.

Ø   There are two forms of litmus: (3) red litmus and (4)      blue litmus.

Both of them are available in solution and paper form.

Ø   (5) Acids turn blue litmus paper red, and (6) alkalis turn red litmus paper blue.

Ø   Distilled water does not change the colours of both blue and red litmus paper. It is said to be (7) neutral.        

3.     Universal indicator and the pH scale

Ø   To show the (8) degree of acidity and alkalinity of a substance, we can use

(9)universal indicator.

Ø   Universal indicator is a mixture of several indicators. It shows different (14) colour in substances with different degrees of acidity or alkalinity.

Ø   Universal indicator is available in solution and paper form. Its paper form is called

(10)  pH paper.

Ø   We usually measure acidity or alkalinity in terms of (11) pH value.

Ø   By matching the colour of universal indicator solution or pH paper with the colour chart provided, we can tell the pH value of the substance tested.

Ø   The scale for measuring acidity or alkalinity in terms of pH values is called the (12) pH scale. Most substances have pH values between 0 and 14.

²  An (13) acid has a pH value smaller than 7. The lower the pH value, the more acidic it is.

²  An (14) alkali has a pH value greater than 7. The higher the pH value, the more alkaline it is.

²  A (15) neutral substance has a pH value equal to 7.