a. If you start with 0.122 g of H 2 , how much H 2 O do you theoretically
make? Calculate the moles of H2, which would be (0.122g/2g/mole), or 0.061 moles of H2. The balanced equation says we'll get 4 moles of water for every four moles of H2 (1 to 1), so we should get 0.061 moles of H2O. Convert that to grams by multiplying by water's molar mass of 18 g/moles.
b. You make 0.745 g of H 2 O in the lab, what is your percent yield? Take the answer from (1.) and divide that by 0.745 g to get percent yield. I judge around 70%, just looking at the numbers.
3. 2Al+ 3Cl 2 → 2AlCl 3
How many grams of AlCl 3 could be produced from 34.0 g Al and 39.0 g
Cl 2 ? Use the same process as above. Calculate the moles of Al in 34.0 grams. Since it is in a 1:1 relationship with the moles of AlCl3, that will be the number of moles of the product produced. Then convert that into grams by multiplying by the molar mass of AlCl3.
4. N 2 + 3H 2 → 2NH 3
a. How many grams of NH 3 will be produced if you have 55.2 g N 2 and
89.7 g of H 2 ? Use the same process. But now we have a molar ratio of 2:1 between the NH3 and N2, so multiply the value of moles you get for the N2 by 2 to get moles of NH3. Before you do that, however, we need to find out if there is enough H2 for this reaction. The equation says we need three moles of H2 for every one mole of N2. Calculate how many moles we have of both the H2 and N2 by dividing their masses by their molar mass. I get 1.97 moles for N2 and 44.85 moles of H2. We need three times as much hydrogen than nitrogen, and we can see we have far more than that. That makes nitrogen the limiting reagent. Use the moles of N2 in calculating the grams of NH3 using the technique above.
b. What are your limiting reagents? Answered just above.
5. C 3 H 8 + 5O 2 → 3CO 2 + 4H 2 O
a. If you have 17.6 g of C 3 H 8 and 36.2 g of O 2 , how much CO 2 will be
made? I've run out of time. Sorry. Use the same principles as the previous problem. Convert to moles and determine which reagent is limiting before using that reagent to calculate the amount of CO2 made.
b. What is your limiting reagent?
I hope this helps,