5.5 Acids Alkali and Nutralisation

7/28/2019 5.5 Acids Alkali and Nutralisation

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ACIDS

An acids is substance that produces hydrogen ions when dissolved in water.

Some acids are found naturally in living things and are called organic acids.They are usually weak acids and less corrosive.

Inorganic acids or mineral acids obtain from manufactured from mineralsalt. Inorganic acids are usually strong and more corrosive.


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Organic acids


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The Properties of Acids


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The Properties of Alkalis


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The properties of Acids The properties of Alkalis

Taste sour

pH value less than 7

Turnsbluelitmus paperred Corrosive

React with metals to produce

hydrogen gas

React with carbonates to

release carbon dioxide gas

Neutralise alkalis to form

salt andwater

Tastebitter

Feel soapy(slippery)

pH greater than 7 Turns red litmus paper

blue

Corrosive

React with ammonium salt

to release ammonia gas

when heated

Neutralise acids to form

andwater

Acids and alkalis only show their properties in the

presence of water.

Substances with pH 7 are neutral.

The pH range is from 1 to 14.


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Uses of acid and alkali in everyday life


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NEUTRALISATION

Neutralisation is a chemical reaction between an acid

and alkali to form a salt andwater. Neutralisation can berepresented by thewords equation:

Reactions of various kinds of acids and alkalis will producedifferent types of salts.

Titration is a process where an acid is gradually addedfrom a burette to an alkali until the end point of

neutralisation is reach.

ACIDS + ALKALI SALT + WATER

Hydrochloric acid + sodium hydroxide sodium chloride + water

Sulphuric acids + calcium hydroxide calcium sulphate + water

Nitric acids + ammonium hydroxide ammonium nitrate + water


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Activity 5.12Aim : To investigate neutralisation between hydrochloric acid and sodium hydroxide

Discussion:

1. Why do we need to add in the phenolphtalein indicator?

2. Why must we add in the acids slowly?

3. Write a word equation to represent the neutralisation.


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Activity 5.12Aim : To investigate neutralisation between hydrochloric acid and sodium hydroxide

Discussion:

1. Why do we need to add in the phenolphthalein indicator?

Phenolphthalein indicator will change colour to indicate theend point is reached.

2. What is the colour and taste of the substance obtained afterevaporating the solution to dryness?

The substance is white and tastes salty

3. Write a word equation to represent the neutralisation.

Hydrochloric acid + Sodium hydroxide Sodium chloride +

waterConclusion:

When an alkal i is neutral ised by an acid, salt and

water are form ed


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Toothpaste (alkali) Neutralise acid in mouth

Antacid (alkali) Neutralise excessive hydrochloric acid in

stomach

Hair conditioner

(acid)

Neutralise alkaline shampoo residue on

the hair

Bee sting (formic

acid)

Ant bites

Treated with baking soda mixed with

water, calamine lotion

Wasp stings

(alkaline)

Treated with vinegar

Chemical burns

caused by alkalis

Treated by washing with weak acids such

as boric acid or vinegar

Acidic soil Treated by adding lime (alkali) to the soil

Application of neutralisation in daily life

5.5 Acids Alkali and Nutralisation

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