HARDMCQ SINGLEIChO (Chemistry Olympiad)Physical ChemistryMole _ Equivalent ConceptAchiever Section

When a hydrate of Na₂CO₃ is heated until all the water is removed, it loses 54.3 per cent of its mass. The formula of the hydrate is

A.Na₂CO₃.10H₂O

B.Na₂CO₃.7 H₂O✓ Correct

C.Na₂CO₃.5 H₂O

D.Na₂CO₃. 3H₂O

Explanation

Given, Mass of sodium carbonate M = 106 g/mol Let, Mass of water present molecules present in hydrate state = x Mass of hydrated sodium carbonate = M +x Therefore, 54.3% x 100/M+x 54.3% x 100/106+x x=125.94g/mol No. of water molecules -125.94/18=7 x x The formula of the hydrate is 2 3 2 Na CO .7H O .

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