   # What amount (moles) is represented by each of these samples? a. 20.0 mg caffeine, C 8 H 10 N 4 O 2 b. 2.72 × 10 21 molecules of ethanol, C 2 H 5 OH c. 1.50 g of dry ice, CO 2 ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243

#### Solutions

Chapter
Section ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243
Chapter 5, Problem 66E
Textbook Problem
63 views

## What amount (moles) is represented by each of these samples?a. 20.0 mg caffeine, C8H10N4O2b. 2.72 × 1021 molecules of ethanol, C2H5OHc. 1.50 g of dry ice, CO2

(a)

Interpretation Introduction

Interpretation: The amount (moles) of compound is to be calculated from the given samples.

Concept introduction: The atomic mass is defined as the sum of number of protons and number of neutrons.

Molar mass of a substance is defined as the mass of the substance in gram of one mole of that compound.

The molar mass of any compound can be calculated by adding of atomic weight of individual atoms present in it.

The amount of substance containing 12g of pure carbon is called a mole. One mole of atoms always contains 6.022×1023 molecules. The number of molecules in one mole is also called Avogadro’s number.

To determine: The amount (moles) of compound in 20.0mg of C8H10N4O2 .

### Explanation of Solution

Given

The mass of C8H10N4O2 is 20.0mg .

The molar mass of C8H10N4O2 is,

(8×12.01+10×1.008+4×14.0+2×15.999)g/mol=194.158g/mol

The conversion of milligram (mg) into gram (g) is done as,

1mg=103g

Hence, the conversion of 20.0mg into gram is,

20.0mg=(20.0×103)g=20×103g

Formula

The number of moles in C8H10N4O2 is calculated as,

MolesofC8

(b)

Interpretation Introduction

Interpretation: The amount (moles) of compound is to be calculated from the given samples.

Concept introduction: The atomic mass is defined as the sum of number of protons and number of neutrons.

Molar mass of a substance is defined as the mass of the substance in gram of one mole of that compound.

The molar mass of any compound can be calculated by adding of atomic weight of individual atoms present in it.

The amount of substance containing 12g of pure carbon is called a mole. One mole of atoms always contains 6.022×1023 molecules. The number of molecules in one mole is also called Avogadro’s number.

To determine: The amount (moles) of compound in 2.72×1021molecules of C2H5OH .

(c)

Interpretation Introduction

Interpretation: The amount (moles) of compound is to be calculated from the given samples.

Concept introduction: The atomic mass is defined as the sum of number of protons and number of neutrons.

Molar mass of a substance is defined as the mass of the substance in gram of one mole of that compound.

The molar mass of any compound can be calculated by adding of atomic weight of individual atoms present in it.

The amount of substance containing 12g of pure carbon is called a mole. One mole of atoms always contains 6.022×1023 molecules. The number of molecules in one mole is also called Avogadro’s number.

To determine: The amount (moles) of compound in 1.50g of CO2 .

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