An alloy of metals X and Y weighs 12 g and contains atoms X and Y in the ratio of 2:5. The percentage by mass of X in the sample is 20. If atomic mass of X is 40, what is the atomic mass of metal Y?

Explanation

`"Mass of metal X in the alloy"=(20)/(100)xx12=2.40g`
`"Mass of metal Y in the alloy"=12-2.4=9.6g`
`"No. of atoms of X in 2.40 g of X"=(2.40)/(40)xx6.022xx10^(23)=3.61xx10^(22)` ltBrgt `"Ratio of atoms X and Y"=2:5`
`therefore" No. of atoms of Y in the alloy"=(5)/(2)xx3.61xx10^(22)=9.025xx10^(22)`
Thus, `9.025xx10^(22)` atoms of Y have mass = 9.6 g
`therefore" "6.022xx10^(23)" atoms of Y will have mass"=(9.6)/(9.025xx10^(2))xx6.022xx10^(23)g=64.0g`
Hence, atomic mass of Y = 64 amu.