Question

The amount of solute required to prepare 10 litres of decimolar solution is:
A. 0.01mole
B. 0.2mole
C. 0.05mole
D. 1.0mole

Answer 1

Hint: We simply know that molar mass is weight of the substance multiplied by the number of atoms and every mole or gram equivalent contains equal number of atoms that is 6.022$ \times {10^{23}}$.

Complete step by step answer:
From Avogadro’s law it is known that equal volumes of all gases contain equal numbers of molecules under similar conditions. Now since one mole of molecules of all gases contain the same number (6.022$ \times {10^{23}}$ ) of molecules, therefore they occupy the same volume under similar pressure and temperature. The mass of one mole of atoms is exactly equal to the atomic mass in grams of that element.
Let us understand what a decimolar solution is, it is a solution having 1/10th concentration of molar solution such that 1/10th of mole of solute is dissolved in 1L of solution. Hence we can say 0.1 mole of solute is dissolved in ${10^{ - 3}}{m^3}$ volume of the solution. Molarity is given by the number of moles of solute in volume of solution in litres. Therefore to prepare 10 litres of decimolar solution the amount of solute required is,
Decimolar solution M = 0.1
Volume = 10 L
$M = \dfrac{n}{V} \\
0.1 = \dfrac{n}{{10}} \\
n = 1mole \\$
Hence the number of moles of solute in decimolar solution of volume 10 L is 1 mole.

Note: It is extremely convenient to use the law of gram equivalents to solve problems based on chemical reactions. According to this law ‘ the number of gram equivalents of all reactants are equal to each other in a reaction assuming none of them are in excess and is also equal to the number of gram equivalents of all products’. Assuming that all the reactants are undergoing in the reaction.