Question

calculate the no of molecules of :
#phosphorus in 18 g of phosphorus powder.
#copper in 26g of copper powder
#calcium ions present in 0.86g of calcium sulphate
# magnesium ions present in 0.126g of magnesium chloride

Answer 1

No:of moles of P4=18÷(31×4)=. 064

no:of molecules=6. 022×10*23×0. 064=3.
854×10*22
copper=18÷63. 5 =0. 28moles
=0. 28×6. 022×10*23=1. 707×10*23Cu
mass of CaSO4=136
136g of CaSO4contains 40g Ca,therefore 1mol Ca,. 86g contains(.86÷136)=6.323×10*-3 moles of Ca,
therefore 6.323×10*-3×6.022×10*23=3.808×10*21
no:of moles of Mg2+=0.126÷95.3=1.92×10*-3
no:of molecules=1.92×10*-3×6.022×10*23=1.16×10*21