Percentage Compositions using RAMs (1 Viewer)

[`kyttie]

I'd love some kind of help on this, as I'm fairly confused.

Here's the question:

Ammonium sulfate (NH4)2SO4 is commonly used as a nitrogenous fertiliser. How much ammonium sulfate is needed to supply 100g nitrogen?

I don't even have the first clue.



Mind you, that same sheet is all about percentage compositions using RAMs (relative atomic masses). So say in the beginning I had:

Find the % composition by Mass of Mg in MgO

Then it's = RAM Mg x 100= 24.31 x 100 = 60.31%
RAM MgO 24.31+16

So.. how would you tackle the original question, using RAMs?

Thankies in advance.





Kaitlyn.

 

[`kyttie]

M'kay, after making up my own method based on what seems logical,
I got an answer of: 3800.36g of ammonium sulfate are needed to supply 100g of nitrogen.

How did I get this? I found the % composition of each element:
N2 = 2.13%
H8 = 6.11%
S = 24.28%
O4 = 48.42%

Then I reasoned that, since 2.13% of nitrogen equalled 100g, then I'll divide all the other percentages by 2.13% and multiply by 100g to get what they actually are.
So, we already know that: N2 = 2.13% = 100g
Then:
H8 = 6.11% = 287g
S = 24.28% = 1 140g
O4 = 48.42% = 2 273.3g

And, adding them all together you get 3800.36g = my answer.

Now - firstly, I'm wondering if that's even right, or a valid method, since I just made it up.
Secondly... why don't my percentages add up to 100%? Probably a calculation error, but argh - where?



Kaitlyn.

 

[airie]

Hey there :wave: Maybe you should ask Conroy to explain more too

How did I get this? I found the % composition of each element:
N2 = 2.13%
H8 = 6.11%
S = 24.28%
O4 = 48.42%

How did you find those? If by mass, percentage of nitrogen in ammonium sulphate would be 2*14/(2*14+8*1.008+32.07+4*16)=21.2%, not 2.13%. And anyway, you could see that these percentages are wrong, seeing that your hydrogen percentage is almost thrice that of nitrogen, which is, uhh, hardly achievable given their ratio in the empirical formula...

So 21.2% of the substance is 100g, thus the total mass of the substance is just 100/[2*14/(2*14+8*1.008+32.07+4*16)]=471.907...=471.91g (2d.p.). You don't need to go through the percentages of all other compositions and add them up

 

[`kyttie]

Heh yeah, the H being almost three times N was a bit dodgy.
Stupid calculation errors. :mad1:

Anyhow, I ended up working out the rest but I don't get your last paragraph.
Why do you divide 100, by N2, by the rest?




Kaitlyn.

PS: I have Gouliaev. :mad1:

 

[airie]

Divide the mass of nitrogen by its percentage composition to get the mass of the whole compound. That long thing I divided 100g by is just the exact percentage of nitrogen in ammonium sulphate (around 21.2%, but that's not the exact percentage, remember)

Btw, I thought Gouliaev's good. I've got friends in her class. Anyway, we should stop there