   Chapter 2, Problem 139GQ

Chapter
Section
Textbook Problem

Chromium is obtained by heating chromium(III) oxide with carbon. Calculate the mass percent of chromium in the oxide, and then use this value to calculate the quantity of Cr2O3 required to produce 850 kg of chromium metal.

Interpretation Introduction

Interpretation: The mass percent of chromium in Cr2O3 and the mass of Cr2O3 that must be used to produce 850kg of chromium have to be determined.

Concept introduction:

• Moles: One mole is equivalent to the mass of the substance consists same number of units equal to the atoms present in 12g of 12C.
• From given mass of substance moles could be calculated by using the following formula,

Molesofsubstance GivenmassofsubstanceMolecularmass

• 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)
• Mass percentage is one way to represent the concentration of an element in a compound or a component in a mixture. 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

Mass percent of elements of a compound is the ratio of mass of element to the mass of whole compound and multiplied with hundred.

The molecular formula of chromium (III) oxide is Cr2O3 and its molar mass is 152g/mol

Then, the mass percent of chromium in Cr2O3 can be calculated as follows,

MolarMassofCrinthecompound =2×52=104g/molMasspercentofCrinCr2O3=MolarmassofCr

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