Testing for cations sim

What the sim shows

Each tube holds 2.0 cm³ of a 0.1 mol/dm³ solution of one cation. Each drop is 0.05 cm³ of 1.0 mol/dm³ reagent. Add a few drops and note the colour of the precipitate, then add more until the reagent is clearly in excess and note whether the precipitate dissolves completely. Copper(II) gives a pale blue precipitate, iron(II) green and iron(III) red-brown; calcium, zinc, aluminium and lead(II) give white. In excess sodium hydroxide the amphoteric hydroxides of zinc, aluminium and lead(II) dissolve to a colourless solution; calcium's stays. Aqueous ammonia is a weak alkali: calcium gives no precipitate, only zinc's white precipitate dissolves in excess, and copper(II)'s pale blue precipitate dissolves to a dark blue solution. Ammonium gives no precipitate, but warmed with sodium hydroxide it gives off ammonia, which turns damp red litmus blue. A tube tested with the other reagent is refilled with a fresh portion first.

• Precipitate and solution colours are true colours
• Tubes are numbered on the rack

Use it in your lessons

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