Chapter U1.9, Problem 5E

Interpretation Introduction

(a)

Interpretation:

The chemical formula of compound that is formed during the reaction of calcium with sulfur needs to be determined.

Concept introduction:

Element is the basic unit of any substance which can combine with same or different elements to form molecules and compounds. Elements are composed of same type of atoms therefore they exhibit unique physical and chemical properties.

The chemical reaction of two or more elements leads to the formation of new molecules and compounds.

Answer to Problem 5E

The reaction of calcium with sulfur forms calcium sulfide and the reaction is as follows:

$\text{Ca + S}\stackrel{}{\to }\text{ CaS}$

Explanation of Solution

The reaction of calcium with sulfur forms calcium sulfide as follows:

$\text{Ca + S}\stackrel{}{\to }\text{ CaS}$

The chemical formula of any compound depends on the valency of the bonded atoms. In calcium sulfide, both Ca and S has valency 2. Therefore, the simple ratio of Ca and S must be 1:1 that makes the chemical formula of calcium sulfide as CaS.

Interpretation Introduction

(b)

Interpretation:

Whether the mass of compound formed by Ca and O has higher mass or the compound formed by Ca and S has higher mass needs to be determined.

Concept introduction:

Element is the basic unit of any substance which can combine with same or different elements to form molecules and compounds. Elements are composed of the same type of atoms therefore they exhibit unique physical and chemical properties.

The chemical reaction of two or more elements leads to the formation of new molecules and compounds.

Answer to Problem 5E

CaS have higher mass as compared to CaO.

Explanation of Solution

The reaction of calcium with sulfur forms calcium sulfide as follows:

$\text{Ca + S}\stackrel{}{\to }\text{ CaS}$

Similarly, the reaction of calcium with oxygen forms calcium oxide as follows:

${\text{2 Ca + O}}_{\text{2}}\stackrel{}{\to }\text{ 2 CaO}$

In both compounds; Ca is common element whereas O and S are not same in both compounds. The atomic mass of O is 16u and atomic mass of S is 32u.

Since the molecular mass of any compound is sum of atomic masses of atoms present in it thus the molecular mass of CaO must be 40u + 16u = 56 u whereas mass of CaS will be 40u + 32u = 72 u.

Hence CaS must have higher mass than CaO.