The diagram shows the process of adding calcium nitrate and strontium nitrate to separate boiling tubes and heating them. Identical conditions are used.

11.4.1 describe and interpret, in terms of changes in oxidation number, the reaction of chlorine with cold and with hot aqueous sodium hydroxide and recognise these as disproportionation reactions

11.4.2 explain, including by use of an equation, the use of chlorine in water purification to include the production of the active species HOCl and which kill bacteria.