Question:

If $300\,mL$ of a gas weighs $0.368\, g$ at $STP$. What is its molecular weight?

Updated On: Jun 8, 2024
  • 30.16 g
  • 2.55 g
  • 27.5 g
  • 37.5 g
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The Correct Option is C

Approach Solution - 1

At STP, $\because$ Weight of $300\, mL$ of gas
$=0.368\, g$
$\therefore$ Weight of $22400\, mL$ of gas
$=\frac{0.368 \times 2240}{300} g / mol$
$=27.47\, g / mol$
$=27.5\, g / mol$
$\because$ Molecular weight of the gas is $27.5\,g$
$[\because 22400\, mL$ of a gas contains amount equal to molecular weight of the gas.]
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Approach Solution -2

Ans: Molecular weight is the atomic mass unit of each of the atoms present in the compound. 

One mole of gas occupies a volume of 22.4 L at STP ( standard temperature and pressure) where temperature is 273 K and pressure of 1 atm.

 Now, according to the question, 

Weight of 300ml of the gas is 0.368g 

So, weight of 22400 ml of gas will be = 0.368 x 22400/300 

= 27.47 g/mol 

So, as one mole of gas occupies 22.4L, therefore,the weight will be the molecular weight of the gas. 

 

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Concepts Used:

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.
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Read More: Some Basic Concepts of Chemistry

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.