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# Chemistry calculations watch

1. I need help on moles calculations. I've checked a revision guide with no luck.

Mg + N2 = Mg3N2
I am given that 5 kg of magnesium was burnt inair so I have to find out the mass of magnesium nitride produced assuming air is 4/5th nitrogen.

1. balance equation 3Mg + N2 = 3MgN2 (am i right?)
2. find number of moles of Mg used. 5000 divide by 24 = 208 moles ?
3. work out number of moles of magnesium nitride produced. ???
4. find molar mass of magnesium nitride. ???
5. Find mass of Magnesium nitride produced burnt in N2. ???
6. Find mass of magnesium nitride produced if burnt in air. ???

Another question I'm completely stuck on.

Ca(OH)2 + CO2 = CaCO3 + H20
What volume of Co2 is needed to react with 100cm3 of 0.1 mol dm-3 calcium hydroxide.
1 Find number of moles of calcium hydroxide
2 Work out te number of moles of C02
3 Find out the volume of C02 needed

All help will be so grateful
2. (Original post by angelic_fairy)
I need help on moles calculations. I've checked a revision guide with no luck.

Mg + N2 = Mg3N2
I am given that 5 kg of magnesium was burnt inair so I have to find out the mass of magnesium nitride produced assuming air is 4/5th nitrogen.

1. balance equation 3Mg + N2 = 3MgN2 (am i right?)
2. find number of moles of Mg used. 5000 divide by 24 = 208 moles ?
3. work out number of moles of magnesium nitride produced. ???
4. find molar mass of magnesium nitride. ???
5. Find mass of Magnesium nitride produced burnt in N2. ???
6. Find mass of magnesium nitride produced if burnt in air. ???

Another question I'm completely stuck on.

Ca(OH)2 + CO2 = CaCO3 + H20
What volume of Co2 is needed to react with 100cm3 of 0.1 mol dm-3 calcium hydroxide.
1 Find number of moles of calcium hydroxide
2 Work out te number of moles of C02
3 Find out the volume of C02 needed

All help will be so grateful
For the second question i think you do it like this:

1. moles = concentration * Volume

moles = 0.100 * (100/1000)
=0.01 moles

2. 1 : 1 ratio
So moles of CO2 is 0.01 moles

3. volume = moles * 24

volume = 0.01 * 24
volume =0.24 dm3

I think this is right i may be wrong...
3. Thnx sooo much. Anyone have any answers for the first Q? Would like to get a good mark in this seeing as I've done real bad in the subject and the teacher's starting to have a dislike to me more and more.
4. (Original post by angelic_fairy)
I need help on moles calculations. I've checked a revision guide with no luck.

Mg + N2 = Mg3N2
I am given that 5 kg of magnesium was burnt inair so I have to find out the mass of magnesium nitride produced assuming air is 4/5th nitrogen.

1. balance equation 3Mg + N2 = 3MgN2 (am i right?)

All help will be so grateful

1. no, it's 3Mg + 2N2 = Mg3(N2)2
5. (Original post by scottygar)
1. no, it's 3Mg + 2N2 = Mg3(N2)2
Actually the chemical structure is 3Mg+N2=Mg3N2, the formula Mg3(N2)2
leaves the N2 ion having 13 electrons which is a dimer and the structure's bond angle is bent so much that its making is endothemic.

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