Oh wow, I wish you all the best, and from what I've seen in your VM, I can say quite confidently that you are pretty much set for it. I have to commend you for so quickly absorbing all that material in such little time though! Well done!
More or less, but not in all cases. You will have to take the molar ratio of reactants into consideration. For example, in the equation:
CS2(l) + 2NH3(g) ->NH4SCN(s) + H2S(g)
You see that for every 1 mole of CS2, you need 2 moles of NH3 to react. Let's put some numbers for this example. You have 9g of CS2 and 3g of NH3. What is the maximum number of grams of NH4SCN you can form?
First, you'll want to look at the number of moles of both reactants you have.
From the masses, you divide by the molar masses to find the number of moles of each substance you have. And that should get you 0.204 moles of CS2 and 0.176 moles of NH3. Just by looking at this, you would think NH3 is the limiting reagent, but it's not. You have to consider the 1:2 molar ratio in the equation as well.
Let's assume CS2 is the limiting reagent. With 0.204 mol CS2, we'll need (0.204*2) mol NH3, which equals 0.408 mol NH3. But do we have that much NH3? No. So let's assume NH3 is the limiting reagent. (This part is actually unnecessary, because if you know one reagent is not limiting, then automatically the other one is, but I'm just doing it to illustrate a point.) For every 1 mol of NH3, we'll need 0.5 mol of CS2, correct? So with 0.176 mol NH3, we'll need only 0.088 mol CS2. And there we have it: NH3 is the limiting reagent.
So you work out the moles of product you form from the equation:
For every 1 mole of NH3 you have, you only produce 0.5 moles of NH4SCN. (Which is the same number of moles as CS2, if you've been paying attention. XD) So, you have 0.088 mol product formed, correct? You multiply by the molar mass and get the mass of product formed, which should be 6.70g. Try it yourself to see if you can work through to get the same answer.
Yes. You can also convert the mass of oxygen combusted because there is a limit to the amount of O2 methane consumes during combustion. But you will need to know the mass/volume of O2 used.
You have the magnesium hydroxide method nailed. And after reading the ethanol/gasoline one, you've also got that process right as well.
You'll do fine for that test! You've already got everything down. Good job on getting it so quickly, again!