Question

How many moles of compound are there in the following?
a. 6.60 g (NH4)2SO4
b. . 4.5 kg Ca(OH)2

Answer 1

a) (NH4)2SO4 --- 1 mole of it contains 2 moles of N, 8 moles of H, 1 mole of S, and 4 moles of O.

MM = (2 moles N x 14.0 g/mole) + (8 moles H x 1.01 g/mole) + (1 mole S x 32.1 g/mole) + (4 moles O x 16.0 g/mole) = 132 g/mole.

6.60 g (NH4)2SO4 x (1 mole (NH4)2SO4 / 132 g (NH4)2SO4) = 0.0500 moles (NH4)2SO4

b) The molar mass for Ca(OH)2 = 74.0 g/mole, calculated like (NH4)2SO4 above.

4.5 kg Ca(OH)2 x (1000 g / 1 kg) x (1 mole Ca(OH)2 / 74.0 g Ca(OH)2) = 60.8 moles Ca(OH)2

Answer 2

The number of mole in the compounds are:

A. 6.60 g of (NH₄)₂SO₄ contains 0.05 mole.

B. 4.5 kg Ca(OH)₂ contains 60.81 moles

The mole of a substance is related to its mass and molar mass according to the equation:

$Mole = \frac{mass}{molar mass }$

With the above formula, we can obtain the answer to the questions given above. This is illustrated below:

A. Determination of the number of mole in  6.60 g of (NH₄)₂SO₄

Molar mass of (NH₄)₂SO₄ = 2[14 + (4×1)] + 32 + (4×16)

= 2[14 + 4] + 32 + 64

= 2[18] + 32 + 64

= 36 + 32 + 64

= 132 g/mol

Mass of NH₄)₂SO₄ = 6.60 g

Mole of NH₄)₂SO₄ =?

$Mole = \frac{mass}{molar mass }$

Mole of NH₄)₂SO₄ = $\frac{6.6}{132}$

Mole of NH₄)₂SO₄ = 0.05 mole

Thus, 6.60 g of (NH₄)₂SO₄ contains 0.05 mole.

B. Determination of the number of mole in 4.5 kg Ca(OH)₂

Molar mass of Ca(OH)₂ = 40 + 2(16 + 1)

= 40 + 2(17)

= 40 + 34

= 74 g/mol

Mass of Ca(OH)₂ = 4.5 kg

= 4.5 × 1000

= 4500 g

Mole of Ca(OH)₂ =?

$Mole = \frac{mass}{molar mass }$

Mole of Ca(OH)₂ = $\frac{4500}{74}$

Mole of Ca(OH)₂ = 60.81 moles

Thus, 4.5 kg Ca(OH)₂ contains 60.81 moles

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