HELP! Patterns of chemical change mass, aqa chem

Ok we NEVER got taught this.
My cgp book says how to calculate %mass but that isnt what this question from a past paper asks:

'Iron tablets usually contain iron sulphate.
This can be made by reacting iron with sulphuric acid:

Fe + H^2(little 2, below H)SO^4 -> FeSO^4 + H^2

Calculate the mass of iron sulphate that could be obtained from 4g of iron.'

I know the answer, but could someone actually give me a formula with letters so i can work out all types of these equations? thankyou
xx

Reply 1

Excalibur

These types of questions don't have such 'formula', really. You just have to learn how to do them.

4g of iron.
RAM of iron=56
Moles = mass ÷ RAM = 4 ÷ 56 = 1/14

?g of iron sulphate
RMM of iron sulphate=56+32+16x4=152
Moles = 1/14 (same as iron, because they are at a ratio of 1:1)

So mass = moles x RMM = 1/14x152 = 10.9g

Hmm, that seems wrong. Is that the right answer?

Reply 2

Morgan141

There isn't as formula as far as I'm aware, there is only a process that you have to go through. I'll go through it with your example.

Fe + H₂SO₄ -> FeSO₄ + H₂

(the command is [sub] btw)

Firstly work out the relative mass for everything in the formula

Fe = 56
H = 1 x 2 = 2
S = 32
O = 16 x 4 = 64
Total = 154

Then work out the mass of the specific molecules it wants you to work out, so Fe would be 56 and FeSO₄ would be:

56 + 32 + (4 x 16) = 152

We can then say that 56 grams of iron will produce 152 grams of iron sulphate. Therefore 1 gram of iron produces 152/56 grams of iron and 4 grams will produce (152/56) x 4 = 10.9 grams of FeSO₄

Sorry I couldn't get a formula, I hope that clears it up though

edit: damn beaten! :p:

Interesting method though, in the syllabus tiger_vio is doing though moles aren't covered

Reply 3

[mellifluous]

Is the answer to the question 10.8571 grams FeSO^4 (11 grams when rounded) ??

I hope so because i really hate these types of question!

to get this i did 4/56 x (56+32+(16x4)).

Reply 4

[mellifluous]

woah, clearly got beaten while writing post!
Well, whatever, at least i'm right :smile:

Reply 5

tiger_vio

they are accpeting answers between 10.6 and 10.9 :smile:

thanks

Reply 6

butterfly_girl_5

Its in my revision guide too- I never got taught it but its easy:

step 1: write out a balanced equation
step 2: work out the Mr of each substance 9they give it to you)
step 3:check that the total mass of the products = total mass of reactants
step 4: Apply this ratio to the question-

Fe + H2 SO4 -> FeSO4 + H2

theyll give you:
Fe is 56
H is 1
S is 32
O is 16

56 + (2x1) + 32 + (4x16) -> 56 + 32 + (16x4) + (2x1) (check: yes mass does = reactants)

it asks only about iron sulphate so:

56Ar (iron) -> can be reacted to make -> 56 + 32 + (16x4)
56Ar -> 152Ar of iron sulphate
because Ar is relative mass you can say that
56g iron -> 152g iron sulphate

you want 4g of iron sulphate- so to 56/56 x4= 4
so thats how you work out the amount of iron sulphate: 152/56 x4= 10.86 (2dp)

thats the method- so its right unless my mental maths is a bit off

so say

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