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# Have i done this chem question right? watch

1. so the question is about reacting masses

calculate the mass of iron oxide produced if 28g of iron is burnt in the air.

2Fe+1.5O2=Fe2O3

heres what i've done

. find the RFM of Fe and Fe2O3 which was 55.8 and 159.6

. I divided each RFM by the smallest one that i need for this question (55.8)

. 55.8/55.8 = 1 159.6/55.8 = 2.86 (to 3 sig fig)

. Then i did 2.86 x 55.8 = 159.588 grams

i dont think this is right , someone help
2. this will not get many answers in the Relationship forum.
3. (Original post by the bear)
this will not get many answers in the Relationship forum.
aw *******s how do i change it
4. that's not right; you're not working out iron, you're trying to work out iron OXIDE. So you have to use the formula: moles = mass/molar mass and then multiply to get the mass. don't forget to take moles into account too.

tag one of the admins who run this part of the forum to change the tag
aw *******s how do i change it
it's OK i have requested a move.

although Relationships depend on that special chemistry i think you will struggle on this forum
so the question is about reacting masses (which generally makes me wanna kms)

calculate the mass of iron oxide produced if 28g of iron is burnt in the air.

2Fe+1.5O2=Fe2O3

heres what i've done

. find the RFM of Fe and Fe2O3 which was 55.8 and 159.6

. I divided each RFM by the smallest one that i need for this question (55.8)

. 55.8/55.8 = 1 159.6/55.8 = 2.86 (to 3 sig fig)

. Then i did 2.86 x 55.8 = 159.588 grams

i dont think this is right , someone help
How many moles of Fe to begin with?

How many moles of Fe2O3 are produced by each mole of Fe being reacted?

How many moles of Fe2O3 are being produced in this case?

What mass of Fe2O3 is that?
7. (Original post by the bear)
it's OK i have requested a move.

although Relationships depend on that special chemistry i think you will struggle on this forum
ha got em
8. (Original post by saharan_skies)
that's not right; you're not working out iron, you're trying to work out iron OXIDE. So you have to use the formula: moles = mass/molar mass and then multiply to get the mass. don't forget to take moles into account too.

tag one of the admins who run this part of the forum to change the tag
any websites where i can look this stuff up
9. (Original post by MexicanKeith)
How many moles of Fe to begin with?

How many moles of Fe2O3 are produced by each mole of Fe being reacted?

How many moles of Fe2O3 are being produced in this case?

What mass of Fe2O3 is that?
.2 moles ?

. 1 mole ?

. idk

.that's what i'm trying to find out
10. First you need to find the moles of iron by doing moles=mass/RFM, I.e.28/55.8=0.5 moles of iron
In the equation, 2 moles of iron reacts to form 1 mole of iron oxide. Since in the question you have 0.5 moles of iron, you have 0.5/2= 0.25 moles of iron oxide
To find the mass of iron oxide, mass=moles x RFM so mass=0.25x159.6=39.9g. I think this is right.

11. Once you figured out the moles of Fe; you can work out the moles of Fe2O3 because there's a 2:1 mole ratio. To get Fe2O3 you need to divide the mole of Fe by 2 to get it. Then you multiply the molar mass of Fe2O3 (103.8) by the moles (0.25..) to get the answer.

The molar mass of Fe2O3 isn't 103.8, my bad but it's still the same method.
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12. image.jpg (497.8 KB)
.2 moles ?

. 1 mole ?

. idk

.that's what i'm trying to find out
The only equation you need to know is that Mr = m/n

Mr is relative molecular mass
m is mass
n is number of moles

1) 28g of Fe
Mr = 55.8 gmol^-1
so moles of Fe = 28/55.8 = 0.502 moles

2) each mole of Fe produces half a mole of Fe2O3 when reacted

3) In this case 0.502 moles of Fe reacts so is must make 0.502/2= 0.251 moles of Fe2O3

4) n=0.251 moles
Mr= 159.7 gmol^-1
m= 0.251x159.7 = 40.1 grams of product
14. (Original post by StarGirl01)
First you need to find the moles of iron by doing moles=mass/RFM, I.e.28/55.8=0.5 moles of iron
In the equation, 2 moles of iron reacts to form 1 mole of iron oxide. Since in the question you have 0.5 moles of iron, you have 0.5/2= 0.25 moles of iron oxide
To find the mass of iron oxide, mass=moles x RFM so mass=0.25x159.6=39.9g. I think this is right.
(Original post by saharan_skies)

Once you figured out the moles of Fe; you can work out the moles of Fe2O3 because there's a 2:1 mole ratio. To get Fe2O3 you need to divide the mole of Fe by 2 to get it. Then you multiply the molar mass of Fe2O3 (103.8) by the moles (0.25..) to get the answer.

The molar mass of Fe2O3 isn't 103.8, my bad but it's still the same method.
(Original post by MexicanKeith)
The only equation you need to know is that Mr = m/n

Mr is relative molecular mass
m is mass
n is number of moles

1) 28g of Fe
Mr = 55.8 gmol^-1
so moles of Fe = 28/55.8 = 0.502 moles

2) each mole of Fe produces half a mole of Fe2O3 when reacted

3) In this case 0.502 moles of Fe reacts so is must make 0.502/2= 0.251 moles of Fe2O3

4) n=0.251 moles
Mr= 159.7 gmol^-1
m= 0.251x159.7 = 40.1 grams of product
thanks guys

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