# Chapter 2 Atoms, Molecules, and Ions - Study Questions - Page 95g: 119

$M=245.7\ g/mol$ Mass percents: Cu: $25.86\%$ N: $22.80\%$ H: $5.70\%$ S: $13.05\%$ O: $32.55\%$ In 10.5 g of the compound: Cu: $2.72\ g$ $H_2O$: $0.770\ g$

#### Work Step by Step

Atomic weights (g/mol): $Cu: 63.546,\ N: 14.007,\ H:1.0079,\ S:32.06,\ O:15.999$ Molar mass of $Cu(NH_3)_4SO_4\dot{}H_2O$: $M=63.546+4\times14.007+14\times1.0079+32.06+5\times15.999=245.7\ g/mol$ Mass percents: Cu: $63.546/245.7\times100\%=25.86\%$ N: $4\times14.007/245.7\times100\%=22.80\%$ H: $14\times1.0079/245.7\times100\%=5.70\%$ S: $32.06/245.7\times100\%=13.05\%$ O: $5\times15.999/245.7\times100\%=32.55\%$ In 10.5 g of the compound: Cu: $10.5\ g\times\frac{25.86}{100}=2.72\ g$ The molar mass of water is $18.015\ g/mol$: $H_2O$: $10.5\ g\times\frac{18.015}{245.7}=0.770\ g$

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