Question

A compund containg sodium hydrogen sulphur calculate the molecular formula of the anhydrous compund

Answer 1

ElementPercentageRelative number of atomsSimplest RatioNa14.28 %(14.28/23) = 0.62(0.62/0.31) = 2S9.92 %(9.92/32) = 0.31(0.31/0.31) = 1H6.20 %(6.20/1) = 6.20(6.20/0.31) = 20O(100 - 30.4) = 69.6 %(69.6/16) = 4.35(4.35/0.31) = 14
The empirical formula of the compound is Na2S1H20O14. This is the empirical formula of crystalline salt, if in crystalline salt all hydrogen atoms are combined with oxygen only to from water of crystallization, then the emipirical formula of the crystalline salt will be Na2SO4.10H2O.
Emiprical formula mass of crystalline salt = (2x23) + 32 + (4x16) + (10x18) = 322 u.
Molecular mass of the crystalline salt = 322 u
n = (Molecular Mass)/(empirical formula mass) = 322 / 322 = 1
Thus, Molecular formula of crystalline salt = Na2SO4.10H2O
The anhydrous salt will not contain water of crystallization, so the molecular formula of anhydrous salt = Na2SO4.
Molecular mass of anhydrous salt = 322 - 

Answer 2

Explanation:

10H2O. Emiprical formula mass of crystalline salt = (2x23) + 32 + (4x16) + (10x18) = 322 u. The anhydrous salt will not contain water of crystallization, so the molecular formula of anhydrous salt = Na2SO4...

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