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.
