Acids, Bases and Salts

Acids: Hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, ethanoic acid, methanoic acid, citric acid, carbonic acid.

1. Corrosive: Have a look

2. Turns blue litmus paper red

Alkali: Sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia,

1. Can burn skin.

2. Feels slippery.

The pH value

Acidic: less than 7                              Alkali: more than 7               Neutral: Exactly 7



Methyl orange:


11.2 A closer look at acids and alkalis

Acids: how do they show their acidity?

Definition of strong and weak acid. Measure by conductivity meter or pH meter.

The reactions of acid and base

Reaction of acids

Acid + metals -> salt + hydrogen gas

Acid + base -> salt + water

Acid + carbonates -> salt + water + carbon dioxide

Reaction of bases

calcium hydroxide + ammonium chloride -> calcium chloride + water + ammonia

Strong alkali and weak alkali

Special case of ammonia!

Making use of neutralisation

Acidity of soil comes from : rotting of vegetation, heavy use of fertilisers

If soil is too acidic, plants can't grow.

To reduce acidity, (increase the pH), soil is treated with

limestone ( calcium carbonate )

Lime ( calcium oxide )

Slaked lime ( calcium hydroxide )

11.4 A Closer Look at Neutralisation

Neutralisation by alkali (soluble base)

hydrochloric acid + sodium hydroxide -> sodium chloride + water

Since both (acid and alkali) is in aqueous form, let look at the amount of ions in the solution on both side.

Reactant: H+, Cl-, Na+, OH-

Product: Na+, Cl-, H2O

Change the chemical formula into ionic form. Eliminate ions that appears on both sides of the equation. (They are called spectator ions). What is left?

H+  +  OH-   -> H2O

This is the ionic equation for neutralisation of acid and alkali.

Neutralisation by insoluble base (metal oxide)

Hydrochloric acid + magnesium oxide -> magnesium chloride + water

Ions of both side:

Reactant: H+ , Cl-, Mg2+, O2-

Product: Mg2+, Cl- , H2O

Eliminate ions that appears on both sides of equation.

2H+  +  O2-   -> H2O




11.5 Oxides

Oxides are compounds containing oxygen and another element. Or, any element that is oxidised.

Basic oxide: Magnesium oxide, Iron(III) oxide, Copper (II) oxide

Acidic oxide: Carbon dioxide, sulfur dioxide, phosphorus (V) oxide

Amphoteric oxide: Aluminium oxide, zinc oxide

Neutral oxide: carbon monoxide, dinitrogen oxide