Question

For an alloy that consists of 74.9 g copper, 108.0 g zinc, and 7.3 g lead, what are the concentrations of (a) Cu, (b) Zn, and (c) Pb in weight percent? The atomic weights of Cu, Zn, and Pb are 63.54, 65.39, and 207.2 g/mol, respectively.

Answer 1

Based on weight percentage,

a. percentage of copper

Cu(%) = mass of copper / total mass of the alloy

= 74.9/(74.9+108.0+7.3)

= 0.3938=39.38%

b.percentage of zinc

Zn(%) = mass of zinc / total mass

=108.0/(74.9+108.0+7.3)

= 0.5678=56.78%

c.percentage of lead

Pb(%) = mass of the lead / total mass

= 7.3/(74.9+108.0+7.3)

= 0.03838 = 3.838%

Based on atomic number ,

number of moles of copper = mass of copper/ atomic weight of copper

= 74.9/63.54

= 1.179

number of moles of zinc = mass of zinc / atomic weight of zinc

= 108.0/65.39

= 1.652

number of moles of zinc = mass of zinc / atomic weight of zinc

= 7.3/207.2

= 0.0352

% of Cu = 1.179/(1.179+1.652+0.0352)

=0.4113

= 41.13%

% of Zn = 1.652/(1.179+1.652+0.0352)

= 0.5764

= 57.64%

% of Pb = 0.0352/(1.179+1.652+0.0352)

= 0.01228

= 1.228%