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Using density to find the % composition of an alloy

  1. Apr 14, 2008 #1
    1. The problem statement, all variables and given/known data

    The densities (at 25*C) of tin and lead are 7.3 g/cm3 and 11.3 g/cm3 respectively. Plumber's solder is an alloy of tin and lead and has a density of 9.7 g/cm3.

    Estimate the composition by mass, of the two metals in this solder.

    2. Relevant equations

    3. The attempt at a solution

    i assumed the % composition of lead to be X%. so % composition of tin is (100 - X)%.
    using [(X*11.3)/100] + [((100-X)*7.3)/100] = 9.7

    i got % lead as 60% and % tin as 40%.

    but the answers from the book are 30.1% for tin and 69.9% for lead.

    any help!
  2. jcsd
  3. Apr 14, 2008 #2


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    Amount fractions can be measured in weight percent (wt%) or atomic percent (at%), so just writing "%" is ambiguous. Perhaps this explains the difference.
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