Question

12.00 gram sample of brass (alloy of copper and zinc), is reported to

contain 4.21 grams of zinc, report percent mass composition of zinc and
copper.

Answer 1

The percent mass composition of zinc in the brass sample is:

(mass of zinc / total mass of sample) x 100%

(4.21 g / 12.00 g) x 100% = 35.08% zinc

So the brass sample contains 35.08% zinc by mass.

To find the percent mass composition of copper in the sample, you can use the information that the sample is made of copper and zinc only, so you can use the difference between 100% and the percent zinc:

100% - 35.08% = 64.92% copper

So the brass sample contains 64.92% copper by mass.