someone help me on my chemistry homework

[JOE111111]

can someone tell me how to work out a mole and all that

[Gaia]

I'm going to move this to schools and careers.
I'm not incredibly sure what you're asking.
If you want to find the number of moles it's the mass divided by the gram formula mass, or the volume times the concentration.

[JOE111111]

i dont understand how t o rearrange it because sometimes you are only given one part and then you have to work out something to get 2 parts but how if you only are given one thing in the first place.

[Gaia]

Could you write down the question for me?

[JOE111111]

1.the equation for the reaction of magnesium and fluorins is :
Mg + F2 -> MgF2

a)how many moles of fluorine molecules react with one mole of magnesium atoms?
b)what is the relative frmula mass of MgF2?(Ar values: Mg = 24, F =19)



2. the relative atomic mass of oxygen is 16, and that of magnesium is 24. how many times heavier is a magnesium atmo than an oxygen atom?


3. ammonium nitrate (NH4NO3) is used as a fertiliser. what is the percentage mass of nitrogen in it? (ar values = H = 1, N = 14 , O = 16)



4. 22.5% of the mass of a sample of phosphorus chloride is phosphorus. what is the formula oh phosphorus chrloride? (ar values : P=31, Cl = 35.5)




5. hydrogen peroxide, H2O2, decomposes to form water nd oxygen gas. wrtie a balanced equation for this reaction.


6. calcium reats with oxygen like this :

2Ca + o2 -> 2CaO


what mass of oxygen qill react exactly with 60g of calcium?
(Ar values : O = 16 , Ca = 40)





7.a reaction prudeces a product which has a relative formula mass of 80. the total of the relative forumla masses of all the products is 120. what is the pecentage atom economy of thie reaction ?

8. a reaction that could produce 200g of product produces only 140 g what is the percentage yield?

9.if the percentage yiel for a reaction is 100%, 60g of reactant A would make 80g of product C How much of reactant A is needed to make 80 g of product c if the percentage yield of the reaction is only 75%?

[SillyEvee]

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

[Jagger]

My calculator agrees!

[Katrina]

Trashed; banned user.