# The Naked Scientists Forum

#### Aleysha82

• First timers
• Posts: 3
« on: 26/03/2006 14:18:16 »
Hey,

I feel silly asking for help on this question but I have spent 2 hours reading and trying to figure it out myself.  Hope you guys can help.

I will type the question and hopefully you can guide me to the correct answer.

Potassium Peroxydisulfate K2S2O8, and important industrial bleaching agent is produced by the reaction (NH4)2S2O8 + 2KHSO4 = K2S2O8 + 2NH4HSO4

What Mass (in grams) of K2S2O8 would be produced when 50.0G OF (NH4)2S2O8 reacts with 50.0g of KHSO4?

I did attempt trying to do it but I could understand the equation or the way of getting it done.  The question before it asked for the Limiting Reagent between (NH4)2S208 and KHS04 which I worked it out to be (NH4)2S2O8.

Thanks Aleysha

#### wim

• Full Member
• Posts: 66
« Reply #1 on: 26/03/2006 20:22:49 »
50g / 136g/mol *2 = 0,184mol
0,184mol * 270g/mol = 49,63g K2S2O8

136g/mol = MM KHSO4
270g/mol = MM K2S2O8

highschool?

grtz

« Last Edit: 27/03/2006 12:14:18 by wim »

#### daveshorts

• Moderator
• Neilep Level Member
• Posts: 2583
• Physics, Experiments
« Reply #2 on: 27/03/2006 11:56:28 »
Just with some more words so it may make a bit more sense (also wim are the units right for .184?)

first work out how many mols of product each of the reagents would produce:

first how many mols 50g of (NH4)2S2O8 will make:
2*(14+4)+2*32+16*8=228g/mol
50g / 228g/mol = .219mol

How many mols 50g of KHSO4 will make:
50g / (136g/mol *2) = 0.184mol

KHSO4 is the limiting reagent as it will make less of the product so there will be some (NH4)2S2O8  left over.

so you will produce
0.184mol*270g/mol = 49,63g K2S2O8

#### wim

• Full Member
• Posts: 66
« Reply #3 on: 27/03/2006 12:13:33 »
no they are not, I'll quickly edit!

grtz

#### tony6789

• Neilep Level Member
• Posts: 1127
« Reply #4 on: 27/03/2006 15:17:47 »
..............i am only 13......your question is like a forein language to me

- Big T

#### Aleysha82

• First timers
• Posts: 3
« Reply #5 on: 27/03/2006 15:23:31 »
Thank you so much for that it helped me greatly.

It's so much easier when someone explains it using a bit more english ...

Thanks guys

#### daveshorts

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• Physics, Experiments
« Reply #6 on: 27/03/2006 15:37:33 »
Cheers Aleysha glad to be of assistance

Tony, hopefully it will be a language that will make more sense to you in the future. the names are basically just names and I have never heard of them before, I worked everything out from the formulae.

in the same way that H20 means 2 hydrogen atoms and one oxygen atom in a molecule

K2S2O8 means 2 pottasium, 2 sulphur, and 8 oxygen atoms in a molecule like thing, from the question I worked out this is what Potassium Peroxydisulfate was.

the equation tells us how the substances react together, and using a periodic table you can work out how much each substance weighs and so how much of each substance you have got, and how much product you will get.

It shouldn't be too difficult when you come to do it at school

#### Mr Andrew

• Sr. Member
• Posts: 206
• God was primitive man's attempt at Physics.
« Reply #7 on: 07/06/2006 00:02:21 »
Having a good teacher helps too! Mine was amazing! The method that wim and DaveShorts used to solve the question is called stoichiometry. When you get to that in school you'll know what to look for. If you can't do stoich then you shouldn't be a chemist, thus almost anybody who knows what they're talking about on one of the chemistry threads in this forum should be able to do it. If they can't then I have one thing to say to them:

"Learn how to do Stoichiometry like you should have in highschool chemistry class and don't post another reply in a chemistry thread sounding like you know what you're talking about until you can do it in your sleep!"

"His mind is the ultimate weapon!"-MacGyver television series