Acids, Bases and Salts

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Acids, Bases and Salts

1. Acids

Acids are substances that produce hydrogen ions when dissolved in water.

When acids react with metals, it produces a salt and hydrogen gas.

When acids react with carbonates, it produces a salt, water and carbon dioxide gas.

When acids react with metal oxides or metal hydroxides, it produces a salt and water.

Acids turn blue litmus paper red and they are sour.

Acids are corrosive when highly concentrated and conduct electricity in an aqueous state.

2. Bases

Bases are substances that produce salt and water when reacted with acids and alkalis are soluble bases that produce hydroxide ions when dissolved in water.

When alkalis react with acids, it produces a salt and water.

When alkalis react with ammonium salts, it produces a salt, ammonia gas and water.

When alkalis react with metal salts, it produces a salt and metal hydroxide.

Alkalis are soapy, bitter and conduct electricity in an aqueous state.

3. Oxides

Metals burn in air to produce basic and amphoteric oxides.

When metal oxides react with water, it produces a metal hydroxide.

When amphoteric oxides react with alkalis or acids, it produces a salt and water.

When basic oxides react with acids, it produces a salt and water.

Basic oxides have high melting and boiling points.

Non-metals burn in air to produce acidic and neutral oxides.

When acidic oxides react with alkalis, it produces a salt and water.

When acidic oxides react with water, it produces an acid.

4. Measuring pH

When the pH value falls below 7, the substance is acidic.

When the pH value falls above 7, the substance is basic.

When the pH value is 7, the substance is neutral.

As the pH value increases from 1 to 14 for the universal indicator, the colour changes from red to violet.

As the pH value increases from 1 to 14 for methyl orange, the colour changes from red to yellow.

As the pH value increases from 1 to 14 for bromothymol blue, the colour changes from yellow to blue.

As the pH value increases from 1 to 14 for phenolphthalein, the colour changes from colourless to pink.

5. Salts

All nitrates, most chlorides, most sulphates and SPA carbonates are soluble.

Non-SPA salts can be prepared by adding excess solid but only one reactant is soluble.

SPA salts can be prepared by titration where both reactant are soluble.

PbCl2, AgCl2, BaSO4, PbSO4, CaSO4 and most carbonates are insoluble.

Insoluble salts can be prepared by precipitation where both reactants are soluble.