Acids, Bases and Salts

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A substance that has a pH of 7 is neutral (Neither an Acid or Alkali)

Acids have a pH of less than 7.

Bases have a pH of more than 7

Salts are made when an acid reacts with a base, carbonate or metal.

The name of the salt formed depends on the metal in the base and the acid used. For example, salts made using hydrochloric acid are called chlorides.

Acids

Substances with a pH of less than 7 are acids.

The more strongly acidic the solution, the lower its pH number.

Acidic solutions turn blue litmus paper red.

They turn universal indicator paper red if they are strongly acidic, and orange or yellow if they are weakly acidic.

When a Base is dissolved in water, they are known as a Alkali

Bases

Substances that can react with acids and neutralize them to make a salt and water are called bases.

They are usually metal oxides or metal hydroxides.

For example, copper oxide and sodium hydroxide are bases.

Neutral

Neutral solutions have a pH of 7.

They turn Universal Indicator paper Green

Alkalies

Bases that dissolve in water are called alkalies.

Copper oxide is not an alkali because it does not dissolve in water.

Sodium hydroxide is an alkali because it does dissolve in water.

Alkaline solutions have a pH of more than 7.

The stronger the alkali, the higher the pH number.

Alkalis turn red litmus paper blue.

hey turn universal indicator paper dark blue or purple if they are strongly alkaline, and blue-green if they are weakly alkaline.

Ions are charged particles which are formed when atoms, or groups of atoms, lose or gain electrons.

For the examination, you need to know which ions are produced by acids, and which are produced by alkalis.

You will also need to know the ionic equation for neutralisation.

State symbols State symbols are used in symbol equations:

(s) means solid

(l) means liquid (not the same as dissolved in water - see below)

(g) means gas

(aq) means aqueous (dissolved in water)

Acids

When acids dissolve in water they produce aqueous hydrogen ions, H+(aq). For example, looking at hydrochloric acid:

HCl(aq) → H+(aq) + Cl–(aq)

Alkalies

When alkalies dissolve in water they produce aqueous hydroxide ions, OH–(aq). For example, looking at sodium hydroxide:

NaOH(aq) → Na+(aq) + OH–(aq)

Ammonia is slightly different. This is the equation for ammonia in solution:

NH3(aq) + H2O(l) → NH4+(aq) + OH–(aq)

When the H+(aq) ions from an acid react with the OH–(aq) ions from an alkali, a neutralization reaction occurs to form water. This is the equation for the reaction:

H+(aq) + OH–(aq) → H2O(l)

For example, hydrochloric acid and sodium hydroxide solution react together to form water and sodium chloride solution.

The acid contains H+ ions and Cl– ions, and the alkali contains Na+ ions and OH– ions. The H+ ions and OH– ions produce the water, and the Na+ ions and Cl– ions produce the sodium chloride, NaCl(aq).

Acids, Bases and Salts

Acids, Bases and Salts

Neutralisation reactions

Neutralisation Reactions