# Chapter 2 Atoms, Molecules, and Ions - Study Questions - Page 95k: 158

12

#### Work Step by Step

Number of moles of water: $2.16\ g\div 18.015\ g/mol=0.1199\ mol$ Number of moles of potassium to aluminum sulfate: $(4.74-2.16)\ g\div 258.20\ g/mol=0.00999\ mol$ Ratio: $0.1199/0.00999=12.0$ 12 molecules of water per formula unit.

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