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Tamil Nadu Board of Secondary EducationHSC Science Class 11

A Compound on analysis gave Na = 14.31% S = 9.97% H = 6.22% and O = 69.5% calculate the molecular formula of the compound if all the hydrogen in the compound is present in - Chemistry

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Question

A Compound on analysis gave Na = 14.31% S = 9.97% H = 6.22% and O = 69.5% calculate the molecular formula of the compound if all the hydrogen in the compound is present in combination with oxygen as water of crystallization. (molecular mass of the compound is 322).

Numerical

Solution

Element % Relative no. of atoms Simple ratio
Na 14.31 `14.31/23` = 0.62 `0.62/0.31` = 2
S 9.97 `9.97/32` = 0.31 `0.31/0.31` = 1
H 6.22 `6.22/1` = 6.22 `6.22/0.31` = 20
O 69.5 `69.5/16` = 4.34 `4.34/0.31` = 14

∴ Empirical formula = Na2SH20O14

η = `"Molar mass"/"Calculated empirical formula mass"`
= `322/322`

= 1
Na2SH20O14 = (2 × 23) + (1 × 32) + (20 × 1) + (14 × 16)

= 46 + 32 + 20 + 224

= 322
Molecular formula = Na2SH20O14

Since all the hydrogen in the compound present as water

∴ Molecular formula is Na2SH20O14

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Empirical Formula and Molecular Formula
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Chapter 1: Basic Concepts of Chemistry and Chemical Calculations - Evaluation [Page 35]

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Samacheer Kalvi Chemistry - Volume 1 and 2 [English] Class 11 TN Board
Chapter 1 Basic Concepts of Chemistry and Chemical Calculations
Evaluation | Q II. 17) | Page 35
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