Question

The minimum quantity of ${H_2}S$ needed to precipitate 63.5 g of $C{u^{2 + }}$ will be nearly:
A.63.5 g
B.31.7 g
C.34 g
D.20 g

Answer 1

Hint:In the above question where is going find the molecular mass of ${H_2}S$. Molecular mass is a term for the average relative mass of a single-molecule and formula mass is a term used for the sum of the atomic mass of constituents. To solve the above question we must know the atomic mass of the given molecule and molar mass formula like molar mass of Sulphur is 32.065 g/mol.

Complete step by step answer:
Mole is also known as mol, this unit is used to measure large quantities of very small entities such as atoms, molecules, or other specified particles.
Mole is defined as the amount of a substance that contains exactly $6.02214076 \times {10^{23}}$ of the given substance.
The number $6.02214076 \times {10^{23}}$ is known as the Avogadro constant and is denoted by the symbol ‘${N_A}$’. The elementary constant that can be represented in moles can be atoms, molecules, monatomic/polyatomic ions, and other particles like electrons.
$n = \dfrac{N}{{{N_A}}}$
n is the number of moles of the substance.
N is the total number of elementary entities in the sample.
${N_A}$ is the Avogadro constant.

The molar mass of a substance is defined as the total mass of one mole of the substance. It is represented in terms of ‘grams per mole’ (g/mol). The SI unit of this quantity is kg/mol. Molar mass can be determined by the following formula:
 $\text{Molar Mass Of A Compound} = \dfrac{\text{Mass Compounding Rams}}{\text{Number Of Moles}}$
With this above equation, we find the mass of ${H_2}S$ in the $C{u^{2 + }}$ reacted with ${H_2}S$.
\[C{u^{2 + }} + {H_2}S \to CuS + 2{H^ + }\]
$MolesofC{u^{2 + }} = \dfrac{{63.5}}{{63.5}} = 1mole$
With this equation, we find the number of moles $C{u^{2 + }}$ required in the reaction. The number of moles $C{u^{2 + }}$ presents the reaction is one mole.
Hydrogen Sulphide has two elements they are hydrogen and Sulphur.
We have to first find the atomic mass for each element. The element hydrogen has the atomic mass of 1.00784g/mol. Sulphur has an atomic mass of 32.065g/mol.
Count atoms for each element. In the compound hydrogen sulphide has two hydrogen atoms and one Sulphur atom for the compound.
The molar mass can be calculated by multiplying atomic mass and number of atoms present.
Molar mass $ = $ Number of atoms present $ \times $ Atomic mass
$H = 2(1.00784g/mol) = 2.01568g/mol$
$S = 1(32.065g/mol) = 32.065g/mol$
First, find the molar mass as we know the number of atoms for each element. We first calculate the mass of the hydrogen atom is 2.01568 g/mol. We will repeat the same for a mass of Sulphur atoms that is 32.065 g/mol, now we have to add these two masses together to find the total mass of molecules of hydrogen sulphide. The total hydrogen sulphide mass is 34.08068 g/mol.
Molar mass $ = $ 2.01568 $ + $ 32.065 g/mol
Molar mass $ = $ 34.08068 or 34 g/mol
Thus the correct answer for the above question is (C).

Note:
Molecular mass founded by adding the sum of the atomic masses of the atoms in a molecule means it gives the mass of a molecule. Molecular mass is for covalent compounds that contain only nonmetals. Molecular mass should be expressed in g/mol.