[user100]

I have come over a question like this

A product mixture containing glycerol was treated with 0.100 mol ofperiodate (IO4-). Calculate the number of moles of glycerol if the number of thiosulfate (S2O32-) reacted in a titration with the productmixture is 0.044 mol, given the equations below.

2S2O32- + IO4- + 2H+ --> IO3- + S4O6 + H2O

glycerol + 2IO4-   ---> 2CH2O + HCOOH + 2IO3- + H2O


I thought the answer is 0.02 mol but it is wrong.


Could someone help?

[sjb]

I have come over a question from the following link

I thought the answer is 0.02 mol but it is wrong.

http://www.chegg.com/homework-help/questions-and-answers/product-mixture-containing-glycerol-treated-0100-mol-ofperiodate--calculate-number-moles-o-q856877

Could someone help?

Can you copy the question here? Sometimes these links are specific to your login.

[Borek]

Thiosulfate is not SO₃^2-.

How many moles of periodate reacted with thiosulfate?

If so, how many moles of periodate reacted with glycerol?

[user100]

2S2O32-(0.044mol)  + IO4-+ 2H+ --> IO3- + S4O6 + H2O

glycerol + 2IO4-(0.1 mol)  ---> 2CH2O + HCOOH + 2IO3- + H2O 

How many moles of periodate reacted with thiosulfate?

thiosulfate is 0.044 mol, so by ratio IO4- should be 0.022 mol.
is it right?

If so, how many moles of periodate reacted with glycerol?

0.1/2=0.05 mol ?

but how to get the final answer?

well, i have no idea...

[user100]

is anyone on? I really hope someone could help me with this.

[user100]

oh wait...so it should be 0.1 mol - 0.022 mol =0.078 mol?

[user100]

still wrong... well..

[UG]

oh wait...so it should be 0.1 mol - 0.022 mol =0.078 mol?

Thats number of moles of periodate, you are asked for glycerol. Have a look at the stoichiometry of the second reaction.

[user100]

could u make it clearer?
also, I have to answer it as soon as possible..(deadline in an hour.) hope you can give me the answer

[user100]

so perhaps you mean...that is periodate, so glyercol should be 0.078/2=0.039?

[user100]

I see. It's right now. Thanks.

I think I have to ask my lecturer for further explanation later.

[Borek]

This is all about stoichiometric ratios. Do you know how to read chemical equation?