1. a) You figure that out by looking at the chemical equation.
Mg + F2 -> MgF2
There are no numbers in front of any of the compounds, so you know that 1 mole of Mg is reaction with 1 mole of F2 to form 1 mole of MgF2. Suppose you had:
2C + O2 -> 2CO
Then 2 moles of carbon would be reacting with 1 mole of oxygen gas to form 2 moles of carbon monoxide. Does that make sense?
b)Just add the atomic masses of the elements in the compound.
Compund: MgF2--that's 1 Mg and 2 F atoms.
Mass of MgF2=mass Mg+2*mass F
Mass of MgF2=24+2*19=62
2. mass of Mg=(some constant)*mass of O
24=x16
x=1.5
Mg is one and a half times as heavy as O
3.To find the pourcentage of an element in a compound by mass, you have to find the mass of that element in the compound and divide it by the total mass of the compound. Each molecule of NH4NO3 contains 2 N atoms, so the mass of all the N in that molecule is 28g/mol. The total mass of that molecule is 80g/mol.
28g/mol
80g/mol
=.35
35% of that compound, by mass, is N
4. This is just the same problem, in reverse.
5. This is just writing a balanced chemical equation, and would take a while to actually explain without just doing it for you. If you don't get how to do it, repost and I'll explain.
6. First you have to find how many moles of Ca are equal to 60g.
moles Ca=60g/40g/mol=1.5 moles Ca.
Now, figure out how many moles of O2 will react with 1.5 moles of Ca. To find out, look at the balanced chemical equation.
1 mole of O2 will react with 2 moles of Ca, so we can calcuate that .75 moles of O2 will react with 1.5 moles of Ca.
(1.5/2 gives the proportion of the equations. Then mulitply by the number of moles of O2 in the original euqation, in this case, 1)
Now all we have to do is figure out the mass of .75 moles of O2. The mass of 1 mole of O2 is the relative atomic mass of O times two, because there are two O atoms in a molecule of O2
16*2=32 g/mol
m O2=.75moles*32g/mol=24g
So 24 grams of O2 will react completely with 60 grams of Ca
I have to go now, but you should be able to find the answers to all your mole-related chemisty questions here:
http://www.savitapall.com/moles/index.html
It's a website run by my old Chemistry teacher. It's got a whole ton of review notes and summaries. I've linked you right to the mole section, but you can look at everything else up there, if you need help elsewhere.
Good luck!
EV