acid and alkali
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CAMBRIDGE SECONDARY ONE SCIENCE
CHAPTER 7: ACIDS AND ALKALIS
7.1 ACIDS AND ALKALIS
Many things contain acid. Foods that contain acid have sour taste. Lemons and limes taste sour because contain citric acid.Common acids in the laboratory are hydrochloric acid, sulfuric acid and nitric acid.
7.1 ACIDS AND ALKALIS
Citrus fruits contain citric acid
7.1 ACIDS AND ALKALIS
Strong acids are corrosive. Acids can be diluted with water to make them less dangerous. Diluted acids are still harmful or irritant. The bottles have hazard warning labels.
7.1 ACIDS AND ALKALIS
Strong acid is labelled corrosive Diluted acid is labelled irritant
7.1 ACIDS AND ALKALIS
Many cleaning products contain alkali. Strong alkalis are corrosive. Common alkalis found in the laboratory are sodium hydroxide, potassium hydroxide and calcium hydroxide. Alkalis can be diluted with water to make them less dangerous.
7.1 ACIDS AND ALKALIS
All these products contain alkalis
7.2 IS IT AN ACID OR AN ALKALI?
An indicator can be used to tell an acid from an alkali because it has different colours in an acid and an alkali.Some plant materials such as red cabbage, blackcurrant and beetroot make good indicators. Litmus can also be used as indicator.
7.2 IS IT AN ACID OR AN ALKALI?
Substance Litmus colour Red cabbage juice Type of substance Hydrochloric
acid Red Red Acid
Sodium hydroxide
Blue Yellow Alkali
Water Purple Purple Neutral Lemon juice Red Red Acid
Calcium hydroxide
Blue Yellow Alkali
7.2 IS IT AN ACID OR AN ALKALI?
Video on red cabbage juice indicator:
7.3 THE pH SCALE
The pH scale measures how acidic or alkaline a substance is. Universal indicator changes to different colours in different pHs.
A colour chart for Universal Indicator showing the pH scale
7.4 NEUTRALISATION
Acids and alkalis can cancel each other out when you mix them together to make a neutral solution. This is called neutralisation. To neutralise an alkali, you must use the right amount of acid. If you add too much acid, it makes an acidic liquid. If you add too little acid, it stays an alkaline liquid.
7.4 NEUTRALISATION
A burette can be used to neutralise an alkali very accurately. Universal indicator is added to the alkali in the conical flask
7.5 NEUTRALISATION IN ACTION
Applications of
neutralisation
Toothpaste - Toothpaste
contains alkali that neutralises acid produced by bacteria that
feed on food pieces left on
your teeth
Neutralising lakes
- Acid rain changes the pH
of the lakes. Some countries
drop alkalis into the lakes to
neutralise the acid
Growing crops- Farmers
spread lime on the soil to
neutralise the acid so that
plants can grow better