Waste water can contain metal ions such as chromium. Chromium ions can cause damage to the liver and kidneys. Chromium ions can be removed from water by chemical precipitation using hydroxide ions.
(a) Assuming chromium is present as Cr3- , state an equation for its reaction with hydroxide ions, include state symbols. 
(b) State an expression for the solubility product constant, K, for chromium (III) hydroxide. 
(c) The solubility product of chromium (III) hydroxide is 1.00×10-33 mol4 dm-12 at 298 K. Calculate the concentration, in mol dm-3, of Cr3+ in the solution, when chromium (III) hydroxide is precipated. 
1. (a) Two processes used to treat sewage are filtration and chemical precipitation.
(i) Name the type of substance removed by filtration and the equipment used to do this. 
(ii) Name the type of substance removed by chemical precipitation and a chemical used to do this. 
(b) (i) State two advantages of treating drinking water with ozone rather than chlorine. 
(ii) Other than cost, name one disadvantage of treating drinking water with ozone rather than chlorine.