A 6.55 g sample of a mixture of magnesium carbonate and calcium carbonate is tre
ID: 1065200 • Letter: A
Question
A 6.55 g sample of a mixture of magnesium carbonate and calcium carbonate is treated with excess hydrochloric acid. The resulting reaction produces 1.74 L of carbon dioxide gas at 27 C and 741 torr pressure.
a)
Calculate the total number of moles of carbon dioxide that forms from these reactions.
Express your answer using three significant figures.
b) Assuming that the reactions are complete, calculate the percentage by mass of magnesium carbonate in the mixture.
Express your answer using two significant figures.
Explanation / Answer
(a)
Moles of CO2 = PV/RT = ((741/760) atm x 1.74 L )/ (0.082 x 300.15 K)
= 0.0689 moles
(b)
x = mass MgCO3 molar mass =84.4 g/mol
y = mass CaCO3 molar mass = 100 g/mol
x + y = 6.55
x/ 84.4 + y /100= 0.0689
100 x + 84.4 y =581.516
100 x + 84.4 ( 6.55 -x) = 581.516
100 x + 552.82 - 84.4 x = 581.516
x = 1.839 g
% = 1.839 x 100/ 6.54= 28%