Chapter 13, Problem 61GQ

### 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

# If you want a solution that is 0.100 m in ions, what mass of Na2SO4 must you dissolve in 125 g of water? (Assume total dissociation of the ionic solid.)

Interpretation Introduction

Interpretation: Mass of Na2SO4 dissolved has to be determined.

Concept introduction:

Molarity (M): Molarity is number of moles of the solute present in the one liter of the solution.

Molarity (M) =Numberofmolesofsolute1literofsolution

The number of moles of any substance can be determined using the equation

Numberofmole=GivenmassofthesubstanceMolarmass

Explanation

Given,

â€‚Â Molality of Na2SO4 is 0.001â€‰m

â€‚Â Molar mass of Na2SO4 is 142.04â€‰g/mol

â€‚Â Mass of water is 125â€‰gâ€‰=â€‰0.125â€‰kg

Molality of the solution is calculated by the equation,

â€‚Â MolalityÂ (m)Â =Numberâ€‰ofâ€‰molesâ€‰ofâ€‰soluteMassâ€‰ofâ€‰solventâ€‰inâ€‰kg

Number of moles of Na2SO4 is,

â€‚Â NumberÂ ofÂ molesâ€‰=â€‰molalityâ€‰Ã—â€‰massâ€‰ofâ€‰solvent=â€‰0.100â€‰mâ€‰Ã—â€‰0.125â€‰kg=â€‰0

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