just few chemistry questions help??!!?

Question

1. what is the phase of MgN?

2. A volatile liquid was found to have the composition 62.04% carbon, 10.41% Hydrogen, and 27.55 Oxygen by mass. At 100 degree celsius and 1.00atm, 440.ml of the gaseous compound had a mass of 1.673g. the empirical formula is C3H6O.

Calculate the molar mass of the compound
Determine the molecular formula of the compound.

3. CaCO3(s)-> CaO(s)+CO2(g)

When 1.000g of the impure limestone was heated to constant mass, 215mL of gas were evolved at 25 degree celsius and a pressure of 755mmHg. What was the mass percent of the CaCO3.

Answer 1

1. Solid. And it's Mg3N2.

2. Solve the Ideal Gas Law for molar mass.

PV = gRT/MM
MM = gRT/PV = 1.673*0.08206*373/(1*0.440) = 116.4 g/mol
C3H6O is 58 g/mol, so the molecular formula is C6H12O2

3. Solve IGL for moles of CO2 generated, get moles then mass of CaCO3 consumed, compare to total mass.

n = PV/RT = 0.993*0.215/(0.08206*298) = 0.0087 moles
0.087 moles CaCO3 * 100 g/mol = 0.870 grams
87% CaCO3

Answer 2

3. From the equation pV=nRT we can get
n= pV /RT
755/760 = 0.993 atm
215 mL = 0.215 L
25°C = 298 K
n= 0.215(0.993) / 0.08206(298) = 0.00873 mole CO2
mole CO2= mole CaCO3
MM(CaCO3) = 100 g/mol
so we have 100g/mol (0.00873 mol)=0.873 g
Since the impure limestone weights 1.00 g >>87.3% of CaCO3