8.18.1 The characteristic properties of acids and bases

Acids, bases and salts

The characteristic properties of acids and bases

Acids turn blue litmus red.

Acids have are pH 6 and below (the syllabus says that pH values will be integers, no decimals) Acid + metal → metal salt + hydrogen

Acid + base (except carbonates) → salt + water

Acid + metal carbonate → metal salt + carbon dioxide + water

Bases turn red litmus blue. Bases have are pH 8 to 14.

Acid + base → salt + water + (carbon dioxide when the base is a metal carbonate)

All alkalis (except ammonia) will react with ammonium compounds, removing ammonia for example: calcium hydroxide

+ ammonium chloride → calcium chloride + water + ammonia

Neutral substances are pH 7.

 

-Acidity in soil: plants grow at a pH near 7. If it is too acidic or alkaline they will not grow. Acidic soil is fixed by adding lime.

Strong acids: all molecules dissociate to become ions, low pH, high conductivity, weak bonds

Weak acids: only some molecules do, higher pH, low conductivity, strong bonds (weaker effervescence when reacting with carbonates or metal than a strong acid, this property can be used in experimental demonstrations)

Strong alkali: high conductivity and pH, weak bonds, high dissociation

Weak alkali: low conductivity and pH, strong bonds therefore low dissociation In alkalis, more dissociation i.e. higher concentration of OH- ion = higher pH. In acids, higher concentration of H+ ion (proton) = lower pH

Universal indicator is an indicator which can be used as paper or in solution