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CAIE IGCSE Chemistry 7.3.3 Hydrated substance as a substance that

Practise recognising hydrated and anhydrous substances from heating tests, colour changes and removal of chemically combined water.

Syllabus
2026–2028
Course
Chemistry 0620

Exam points

  • state hydrated or anhydrous from descriptions of crystals gaining or losing water
  • link heating hydrated copper(II) sulfate to white anhydrous copper(II) sulfate
  • use repeated heating and weighing to judge when all water has been removed

7.3.3—Hydrated substance as a substance that question 1

[Maximum number: 1]

A student prepares calcium nitrate, Ca(NO3)2\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}, by adding calcium carbonate to dilute nitric acid.

Calcium nitrate crystals are hydrated and have the formula Ca(NO3)2⋅xH2O\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2} \cdot x \mathrm{H}_{2} \mathrm{O} where x is a whole number of molecules of water.

The student heats the crystals to remove the molecules of water.

Ca(NO3)2⋅xH2O( s)→Ca(NO3)2( s)+xH2O( g)\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2} \cdot x \mathrm{H}_{2} \mathrm{O}(\mathrm{~s}) \rightarrow \mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{~s})+x \mathrm{H}_{2} \mathrm{O}(\mathrm{~g})

State the term used to describe the calcium nitrate after the molecules of water have been removed.

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