A)
Let P = the pressure = 74.0 cm Hg = 740 mm Hg
Let V = the volume = 10 L
Let T = the temperature = 25 C = 298 K
Let R = the gas constant = 62.36367 (L•mm Hg)/(K• mole)
Let n = the number of moles of CO2
Using the gas law, (P)(V) = (n)(R)(T), solved for n:
n = {(P)(V)}/{(R)(T)}
n = {(740 mm Hg)(10 L)}/{(298 K)(62.36367 L•mm Hg/K• mole)}
n ≈ 0.3981 moles
Because Calcium Carbonate reacts to produce CO2 in a 1:1 ratio, 0.3981 moles of Calcium Carbonate are needed to produce 0.3981 moles of CO2. The molar mass of Calcium Carbonate is 100 grams per mole (google search)
0.3981 moles(100 grams/mole) = 39.81 grams of Calcium Carbonate.
B)
Density is mass/volume. To make the calculation simple, assume that you have 1 mole and then find its volume. Chlorine gas is diatomic so its molar mass is twice its atomic weight = 70.9 grams/mole. The temperature must be converted to 573 K and the we use the gas law to find the volume but this time we use 0.082 {L•atm}/{K•mole} for the gas constant:
V = n(R)(T)/P
V = 1(0.082)(573)/2.55
V ≈ 18.43 L
D = 70.9 grams/18.43 L
D ≈ 3.9 grams/Liter