EduNinja

CAIE IGCSE Chemistry 7.3.3 Hydrated substance as a substance that

CAIE IGCSE Chemistry 7.3.3 Hydrated substance as a substance that
Cambridge IGCSE Chemistry 0620 syllabus for exams in 2026, 2027 and 20282026–2028

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

How this is tested

  • 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

Question 4(e)(i)

[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.