A student is given a 5.000g sample to analyze composed of tin metal with a small amount of a zinc
impurity. The student dissolves the metal in concentrated nitric acid, allows the reaction to
continue to completion, and heats the mixture to leave 6.341g of solid containing only a tin oxide of
unknown composition and ZnO.
In order to separate the unknown tin oxide from the ZnO, the oxide mixture is dissolved in dilute
hydrochloric acid and treated with hydrogen sulfide. This precipitates the tin as SnS2. The
precipitate is filtered, dried, and weighed to a constant mass. The mass of the precipitate was
7.316g.
a) Calculate the mass percent of tin in the SnS2 precipitate.
b) Calculate the mass percent of tin in the original sample of metal.
c) Calculate the mass of the ZnO formed during the first reaction.
d) Calculate the mass of the tin oxide formed during the first reaction.
e) What is the empirical formula of the tin oxide formed during the first reaction? Justify your
answer.
f) Suppose that the student was unaware of the presence of the zinc impurity. Calculate the
percent yield that student would determine for the first reaction assuming no zinc is present.
g) Give one reason a student who is unaware of the zinc impurity might give for the percent yield
not being 100% that accounts for the results of your calculation in f). Explain your answer.
a) To calculate the mass percent of tin in the SnS2 precipitate, we need to determine the mass of tin in the SnS2 compound and then divide it by the total mass of the compound.
Mass of tin in SnS2 = Mass of SnS2 precipitate - Mass of sulfur in SnS2
The molar mass of SnS2 is:
molar mass of Sn = 118.71 g/mol
molar mass of S = 32.06 g/mol
So, the molar mass of SnS2 is:
molar mass of SnS2 = (1 * molar mass of Sn) + (2 * molar mass of S)
Now, use the molar mass of SnS2 to calculate the mass of tin in the SnS2 precipitate.
Mass of tin in SnS2 = (Mass of SnS2 precipitate) * (molar mass of Sn / molar mass of SnS2)
Now, calculate the mass percent of tin in the SnS2 precipitate:
Mass percent of tin in SnS2 = (Mass of tin in SnS2 / Mass of SnS2 precipitate) * 100
b) To calculate the mass percent of tin in the original sample of metal, we need to divide the mass of tin in the original sample by the total mass of the sample.
Mass of tin in the original sample = (Mass percent of tin in the original sample / 100) * Mass of the original sample
Mass percent of tin in the original sample = (Mass of tin in original sample / Mass of the original sample) * 100
c) To calculate the mass of ZnO formed during the first reaction, we need to subtract the mass of tin oxide formed from the total mass of the solid obtained after heating.
Mass of ZnO = (Mass of solid obtained after heating) - (Mass of tin oxide formed)
d) The mass of the tin oxide formed during the first reaction is equal to the mass of the solid obtained after heating.
Mass of tin oxide formed = Mass of solid obtained after heating
e) To determine the empirical formula of the tin oxide formed during the first reaction, we need to compare the number of moles of tin to oxygen in the tin oxide compound.
First, calculate the number of moles of tin by dividing the mass of tin by its molar mass (118.71 g/mol).
Next, calculate the number of moles of oxygen by dividing the difference between the mass of the tin oxide and the mass of tin by the molar mass of oxygen (16.00 g/mol).
The empirical formula is the simplest whole-number ratio between the moles of tin and oxygen.
f) To calculate the percent yield, we need to divide the actual yield (mass of tin oxide formed) by the theoretical yield (calculated mass of tin oxide that would be formed assuming no zinc impurity) and then multiply by 100.
Percent yield = (Actual yield / Theoretical yield) * 100
g) One reason a student who is unaware of the zinc impurity might give for the percent yield not being 100% is that the presence of the impurity (ZnO) affects the mass of the product formed. The zinc impurity adds additional mass to the solid obtained, leading to a higher measured yield. Since the student is unaware of the impurity, they would assume that all the additional mass is due to the tin oxide, resulting in an inflated percent yield.