# How many moles are there in each sample? a. 45 mg Ag b. 28 kg Zn c. 8 .7 × 10 27 He atoms d. 1 He atom

### Chemistry In Focus

7th Edition
Tro + 1 other
Publisher: Cengage Learning,
ISBN: 9781337399692

Chapter
Section

### Chemistry In Focus

7th Edition
Tro + 1 other
Publisher: Cengage Learning,
ISBN: 9781337399692
Chapter 3, Problem 45E
Textbook Problem
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## How many moles are there in each sample?a. 45 mg Agb. 28 kg Znc. 8 .7 × 10 27 He atomsd. 1 He atom

Interpretation Introduction

Interpretation:

The number of moles present in each sample is to be calculated.

Concept Introduction:

Mole is the unit of the amount of a substance. It relates the number of particles to molar mass.

One mole of a substance contains Avogadro number (6.022×1023) of particles. The number remains constant regardless of the nature of the substance. One mole of an atom contains 6.022×1023 atoms. One mole of a molecule contains 6.022×1023 molecules.

It also relates to the molar mass of substance in grams. The weight of one mole of a substance is equivalent to its molar mass in grams.

To sum up, 1 mole of a substance contains 6.022×1023 particles and weighs the same as its molar mass in grams

### Explanation of Solution

a) 45 mg Ag

Conversion of the mass of Ag from mg to g is as follows:

Mass of Ag = 45 mg (given)1000 mg = 1 g

The number of moles of Ag is calculated as follows:

Molar mass of Ag is 107.9 g.

Number of moles=given massmolar mass

Substitute the values in the above equation:

Hence, the number of moles are 4.2×104 mol Ag.

b) 28 mg Zn

Conversion of the mass of Zn from kg to g is as follows:

Mass of Zn = 28 kg1 kg = 1000 g

The calculation for discerning the moles of Zn is done as follows:

Molar mass of Zn is 65.38 g Zn.

Number of moles=given massmolar mass

Substitute the values in the above equation:

Therefore, the number of moles are .

c) 8.7×1027He atoms

The number of moles of He atom is calculated as follows:

6.022 ×1023 atoms of He = 1 mole of He8.7 ×1027 atoms of He =  1 mole6

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