Question:

The amount of arsenic pentasulphide that can be obtained when 35.5 g arsenic acid is treated with excess ${H_2S}$ in the presence of conc. HCl ( assuming 100% conversion) is :

Updated On: Sep 30, 2024
  • 0.50 mol
  • 0.25 mol
  • 0.125 mol
  • 0.333 mol
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The Correct Option is C

Solution and Explanation

${2H_3 AsO_4 + 5H_2 S ->[Conc\,HCl] As S_5 + 8H_2O }$
2 moles of Arsenic Acid ${->}$ 1 mole of Arsenic Pentasulphide
1 moles of Arsenic Acid ${->}$ 1/2 mole of Arsenic Pentasulphide
$\frac{Molar\,mass\, of\, H_{3}AsO_{4}=141}{Molar\,mass\,of\, As_{2}S_{5}=308} \,$number of moles of $H_{3}AsO_{4}=\frac{35.5}{141}=0.25$
$\therefore$ number of moles of $As_{2}S_{5}=\frac{0.25}{2}=0.125\,mol$
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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.
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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
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