Chapter 2, Problem 150GQ

### 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

# The elements A and Z combine to produce two different compounds: A2Z3 and AZ2. If 0.15 mol of A2Z3 has a mass of 15.9 g and 0.15 mol of AZ2 has a mass of 9.3 g, what are the atomic weights of A and Z?

Interpretation Introduction

Interpretation: The atomic weights of A and Z are needed to be calculated for the given molecules A2Z3 and AZ2 under given conditions.

Concept introduction:

Equation for finding molar mass from mass of a molecule and number moles is,

Molarmass=MassingramsNumberofmoles

• Molar mass of a molecule can be calculated from its molecular formula by taking the sum of atomic masses of all the elements present in it.
• 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

Explanation

Letâ€™s take atomic mass of A and Z as x and y respectively.

The mass and the number of moles of A2Z3 is given that 15.9g and 0.15â€‰mol.

The mass and the number of moles of AZ2 is given that 9.3g and 0.15â€‰mol.

Equation for finding molar mass from mass of a molecule and number moles is,

Â Â Â Â Molarâ€‰massâ€‰â€‰=â€‰â€‰Massâ€‰inâ€‰gramsâ€‰Numberâ€‰ofâ€‰molesÂ

Therefore,

The molar mass of A2Z3 is,

Â Â Â Â Molarâ€‰massâ€‰â€‰=â€‰â€‰15.9g0.15molâ€‰=â€‰106g/mol

The molar mass of AZ2 is,

Â Â Â Â Molarâ€‰massâ€‰â€‰=â€‰â€‰9.3g0.15molâ€‰=â€‰62g/mol

The molecule A2Z3 contains 2A and 3Z atoms, so the molar mass of the compound can written as,

2xâ€‰(atomicâ€‰massâ€‰ofâ€‰A)+3yâ€‰(

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