‘Recycle shipwrecked cargo’ demands group

Pounded by recent storms, this mixture of 5 substances has been reduced to the sample given to you. Local environmental groups have demanded that these five compounds should be separated and either recycled or returned to their original location.

This experiment should take 120 minutes.

Equipment

• Eye protection
• Magnets
• Crucibles
• Evaporating basins
• Test tubes
• Small pyrex, or hard glass test tubes
• Test tube holders
• Filter funnels and papers
• Glass beakers, 100 cm³ maximum
• Glass stirring rods, spatulas
• Rocksil wool
• Bunsen burners
• Tripods
• Gauzes
• Heatproof mats
• Clamp stands
• Top pan balances
• Sodium chloride
• Ammonium chloride
• Silver sand
• Iron filings
• Calcium carbonate
• And a mixture containing 25 g of each of the above chemicals

Health, safety and technical notes 

• Read our standard health and safety guidance here.
• Wear eye protection. 
• This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.
• Ammonium chloride, NH₄Cl (s) is harmful if swallowed and an eye irritant. When it sublimes, do not inhale the vapour. See CLEAPSS Hazcard HC047b

Possible approaches

Each group should be provided with a sample of each component in its pure form, for any preliminary experiments they may wish to do.

Before adding water, it is best to separate (i) the iron filings from the mixture with a magnet, and (ii) the ammonium chloride by sublimation.

Then add water to the remaining sand, calcium carbonate and sodium chloride mixture and filter.

Filtrate of sodium chloride solution is evaporated. Calcium carbonate and sand are left on the filter paper.

Addition of hydrochloric acid to the sand/calcium carbonate mixture forms a solution of calcium chloride (sand removed by filtration).

Addition of sodium carbonate solution precipitates calcium carbonate (by double decomposition).

The calcium carbonate and sand mixture may also be separated by allowing the two components to settle out over a period of several weeks.

Cargo can be anything, e.g. organic material, coloured material becomes a possible extension.

Few students realise that only a small amount of water is needed to dissolve substances. If a large amount of water is used it can take a long time to evaporate (NB, keep large beakers out of reach of students).

Possible extension

Students to write a letter to local environment group with results.