Chapter 4, Problem 26PS

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# A 2.634-g sample containing impure CuCl2 2 H2O was heated. The sample mass after heating to drive off the water was 2.125 g What was the mass percent of CuCl2.2 H2O in the original sample?

Interpretation Introduction

Interpretation:

The mass percent of CuCl2.2H2O in the given sample has to be determined.

Concept introduction:

• The relation between the number of moles and mass of the substance is ,

Numberofmole=MassingramMolarmass

Massingramofthesubstance=Numberofmole×Molarmass

• The molar mass of an element or compound is the mass in grams of 1 mole of that substance, and it is expressed in the unit of grams per mol (g/mol).
• For chemical reaction balanced chemical reaction equation written in accordance with the Law of conservation of mass.
• Law of conservation of mass states that for a reaction total mass of the reactant and product must be equal.
• Stoichiometric factor is a relationship between reactant and product which is obtained from the balanced chemical equation for a particular reaction.
• Amountof substance=Concentrationofsubstance×volumeofthesubstance
• Mass percent of elements of a compound is the ratio of mass of element to the mass of whole compound and multiplied with hundred.
Explanation

Here impure sample of CuCl2.2H2O heating to drive off all the water then the mass of the mixture is reduced from 2.634â€‰g to 2.125â€‰g

From the amount of water involved in the reaction, amount of CuCl2.2H2O can be calculated. Â Both of these components in this reaction react in 1:1 stoichiometric ratio.

Mass of water =â€‰2.634â€‰â€‰gâˆ’â€‰2.125â€‰â€‰gâ€‰=â€‰â€‰0.509â€‰gâ€‰â€‰

Amount of water = 0.509â€‰gâ€‰â€‰18â€‰g/molâ€‰â€‰=â€‰â€‰0.0282â€‰â€‰molâ€‰H2O

Amount of CuCl2 = 0.0282â€‰â€‰molâ€‰H2Oâ€‰â€‰Ã—1â€‰â€‰molâ€‰ofâ€‰CuCl22â€‰â€‰molâ€‰H2Oâ€‰â€‰=0.0141â€‰â€‰molâ€‰CuCl2

Mass of CuCl2=Â  0

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