Question:

A compound, on analysis, gave the following percentage composition: $ Na = 14.31\%, S = 9.97\%, H = 6.22\%, O = 69.5\%$ What would be the molecular formula of the compound assuming that all the hydrogen in the compound is reset in combination with oxygen as water of crystallisation. Molecular weight of the compound is $322$

Updated On: Jun 23, 2023
  • $Na_{2}SO_{4}$
  • $Na_{2}SO_{4}\cdot 10H_{2}O$
  • $Na_{2}SH_{10}O_{12}$
  • $Na_{2}SO_{4} \cdot 7H_{2}O$
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The Correct Option is B

Solution and Explanation

Empirical Formula mass $= 46 + 32 + 20 + 224 = 322$ $n= \frac{\text{Molecular mass}}{\text{Empirical formula mass}} = \frac{322}{322} = 1$ Hence, molecular formula $= Na_{2}SH_{20}O_{14}$ Since, all the hydrogen is in the form of water, thus there are $10H_{2}O$ molecules. Hence, the molecular formula is $ Na_{2}SO_{4} \cdot 10H_{2}O$
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Some Basic Concepts of Chemistry

Chemistry is a vast subject and for understanding its significance we can take help of following points:

  • Chemistry plays an important role in understanding various subjects like physics, geology and biology.
  • Chemistry is a core branch of science that explains us about the various compositional properties and interaction of matter. It also helps to understand various chemical reactions.
  • Chemistry is important in order to understand the behaviour of fertilizers, alkenes, acids, salts, dyes, polymers, drugs, soaps and alloys in organic and inorganic chemistry.
  • Chemistry plays an important role in various fields like healthcare, industrial, research, food, and farm activities.

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Classification of Matter

There are two ways of classifying the matter:

(A) Physical Classification:

Matter can exist in three physical states:

  1. Solids - have definite volume and definite shape
  2. Liquids - have definite volume but not definite shape.
  3. Gases - have neither definite volume nor definite shape.

(B) Chemical Classification:

Based upon the composition, matter can be divided into two main types:

  1. Pure Substances are defined as a single substance (or matter) which cannot be separated by simple physical methods. Pure substances can be further classified as (i) Elements (ii) Compounds
  2. Mixtures are the combination of two or more elements or compounds which are not chemically combined together and may also be present in any proportion.