I need help with some Chemistry questions.

A 37.7-mL volume of an unknown gas is collected over water at 19 degrees Celsius and a total pressure of 770 torr. The mass of the gas is 68.6 mg.

Express all subsequent calculations to the correct number of significant figures.

a. What is the pressure of the “dry” unknown gas?

b. What volume does the gas occupy?

c. How many moles of gas are collected?

d. What is the molar mass of the gas? 

A 1.719-g sample of CaCO3 mixture is thermally decomposed, producing CaO(s) and CO2(g). After the reaction, the mixture has a mass of 1.048g.

a. How many grams and moles of CO2 are evolved?

b. How many moles and grams of CaCO3 are in the mixture?

c. What is the percent CaCO3 in the mixture?

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