The diagram shows part of a technician's method for recovering hydrated magnesium sulfate crystals from a clear magnesium sulfate solution. The solution has...
Question 1 Report
The diagram shows part of a technician's method for recovering hydrated magnesium sulfate crystals from a clear magnesium sulfate solution. The solution has been warmed in an evaporating basin to remove some water. It is then allowed to cool before crystals are filtered. The technician must not heat the basin until it is completely dry because hydrated crystals can lose water of crystallisation. The crystals are intended for a school demonstration, so they should be clean and dry.
(a) Name the process in which liquid water changes to water vapour during warming. [1]
(b) State why the solution is allowed to cool after some water has evaporated. [2]
(c) Give three pieces of apparatus, other than the evaporating basin, needed for the warming stage. [3]
(d) Describe how the crystals should be washed and dried after filtration. [3]
(e) Explain why heating to dryness is unsuitable for preparing hydrated magnesium sulfate crystals. [3]
Answer Details
(a) The change of liquid water into water vapour is evaporation. [1]
(b) Cooling makes the concentrated solution saturated, so magnesium sulfate crystals can form. [2]
(c) Three suitable items are a tripod, gauze and Bunsen burner. A heatproof mat or tongs would also be acceptable. [3]
(d) Rinse the filtered crystals with a small amount of cold distilled water, remove them from the filter paper, then dry them by pressing them between dry filter papers. Cold water minimises dissolving the crystals. [3]
(e) Heating to dryness removes all water. Hydrated magnesium sulfate contains water of crystallisation, and strong heating can remove this bound water and change the crystals. [3]
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