# Chemsitry - Moles Consumed

• Chemistry

## Homework Statement

The overall chemical equation for the titration reaction is:
OCl(aq) + 2 S2O3(aq) + 2H+(aq) 6 Cl(aq) + S2O6(aq) + H2O(R)

If a titration requires 5.29 ml 0.256 M Na2S2O3,
(i) how many moles of S2O32&(aq) were consumed in the titration, and
(ii) how many moles of OCl&(aq) were in the sample?

## The Attempt at a Solution

Ok so what i did was take .245/52.9 and multiplied it by 2 to get .0096 moles of S2O3 consumed....is that right?

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Borek
Mentor
No.

Try to explain what you did and why.

And using numbers that were given in the question won't hurt.

I just realized there is supposed to be an arrow in between the 2H and the Cl; that is where the equation splits into reactants and products.

I'm looking over it again and trying something different. I messed up in the math the first go around

.256/.00529 L = 48.4 mols X 2 (because there are 2 mols S2O3) and that gives me 96.8 mols S2O3; part i

Shouldn't part (ii) just be the 48.4 mols from the previous?

Borek
Mentor
You are still wrong. Check your units.

M = mols/volume

I know M and the volume, so it should be M * volume..not divided..right?

.256 * .00529 = .00135

.00135 * 2 = .0027 mols. Is that right?

Borek
Mentor
Better, but still wrong. You got concentration&volumes&moles part right. Why do you multiply by two if you are calculating number of moles of S2O32-?

I multiplied by 2 because there are 2 S2O3 in the equation. Doesn't that mean you multiply it by two so that your ratio is correct?

Borek
Mentor
Think about it - you put a mole of substance into the baker, but as reaction equation have a 2 in the equation, that means you put 2 moles in the baker? That's what you did now.