# Calculate the mass fraction of zinc in a 50 g sample of ZnS containing 3% impurities.

July 28, 2021 | education

| Given:

m (ZnS) = 50 g

w% (impurities) = 3%

To find:

w% (Zn) -?

Solution:

1) Find the mass of pure zinc sulfide without impurities:

If the proportion of impurities is 3%, then the proportion of pure substance will be 97%

m (ZnS) = 50 g * 0.98 = 49 g.

2) Find the amount of zinc sulfide:

n (ZnS) = m: M = 49 g: 97 g / mol = 0.5 mol

3) Find the mass fraction of zinc in the composition of zinc sulfide according to the following formula:

w% (element) = (Ar (element) * n): Mr (substance) * 100%.

w% (Zn) = (65 * 0.5 mol): 97 * 100% = 32.5: 97 * 100% = 33.5%

Answer: w% (Zn) = 33.5%.

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