   # In 1987 the first substance to act as a superconductor at a temperature above that of liquid nitrogen (77 K) was discovered. The approximate formula of this substance is YBa 2 Cu 3 O 7 . Calculate the percent composition by mass of this material. ### 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 74E
Textbook Problem
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## In 1987 the first substance to act as a superconductor at a temperature above that of liquid nitrogen (77 K) was discovered. The approximate formula of this substance is YBa2Cu3O7. Calculate the percent composition by mass of this material.

Interpretation Introduction

Interpretation: The percentage composition (by mass) of each element in YBa2Cu3O7 compound is to be calculated.

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.

### Explanation of Solution

To determine: The percentage composition (by mass) of each element in YBa2Cu3O7 compound.

The atomic weight of yttrium (Y) is 88.905g/mol . In a compound YBa2Cu3O7 , only one yttrium atom is present. Hence, mass of yttrium in YBa2Cu3O7 is 88.905g/mol .

The atomic weight of oxygen (O) is 15.999g/mol . In a compound YBa2Cu3O7 , seven oxygen atoms are present. Hence, mass of oxygen in YBa2Cu3O7 is,

7×15.999g/molg/mol=111.993g/mol

The atomic weight of barium (Ba) is 137.32g/mol . In a compound YBa2Cu3O7 , two barium atoms are present. Hence, mass of barium in YBa2Cu3O7 is,

2×137.32g/mol=274.64g/mol

The atomic weight of copper (Cu) is 63.546g/mol . In a compound YBa2Cu3O7 , three copper atoms are present. Hence, mass of copper in YBa2Cu3O7 is,

3×63.546g/mol=190.638g/mol

The molar mass is the sum of mass of individual atoms present in it. Hence, molar mass of YBa2Cu3O7 is calculated as,

(88.905+274.64+190.638+111.993)g/mol=666.176g/mol

Formula

The mass percent of element is calculated as,

Mass%ofelement=MassofelementMolarmassofcompound

Substitute the values of mass of yttrium and molar mass of YBa2Cu3O7 in the above equation

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