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# Need help with this question please! watch

1. Attached Images

2. What have you got for the previous parts to the Q and why are you stuck on the last part?
3. (Original post by Pigster)
What have you got for the previous parts to the Q and why are you stuck on the last part?

Well for the last question cos we're looking for the number of moles, I decided to use this formula Number of moles = Number of particle/6.0 x 1023so2 / 6.0x1023 but my answers wrong?!
Attached Images

4. You started with 0.001 mol of I2

0.00063 mol of I2 remained after the SO2 had reacted.

How many mol of I2 must have reacted with SO2?

Applying the second reaction they gave you (the one in part b), how many mol of SO2 were there in the 100 m3?

Attached is a work through of the answers. I hope this helps (pretty much what Pigster was eluding to, so thought I would finish it off as a worked example). If you need any revision notes or questions/model answers etc. check out my 100% free website www.scienceskool.co.uk

Have fun

Alex

6. (Original post by Pigster)
You started with 0.001 mol of I2

0.00063 mol of I2 remained after the SO2 had reacted.

How many mol of I2 must have reacted with SO2?

Applying the second reaction they gave you (the one in part b), how many mol of SO2 were there in the 100 m3?
I see, thank you!
(Original post by ajsullivan)

Attached is a work through of the answers. I hope this helps (pretty much what Pigster was eluding to, so thought I would finish it off as a worked example). If you need any revision notes or questions/model answers etc. check out my 100% free website www.scienceskool.co.uk

Have fun

Alex

Woow, Thaanks a loot!! I'd definitely check it out!!
7. (Original post by Pigster)
You started with 0.001 mol of I2

0.00063 mol of I2 remained after the SO2 had reacted.

How many mol of I2 must have reacted with SO2?

Applying the second reaction they gave you (the one in part b), how many mol of SO2 were there in the 100 m3?
(Original post by ajsullivan)

Attached is a work through of the answers. I hope this helps (pretty much what Pigster was eluding to, so thought I would finish it off as a worked example). If you need any revision notes or questions/model answers etc. check out my 100% free website www.scienceskool.co.uk

Have fun

Alex

Hello there,
Sorry to bother you but I don't understand why you subtracted the remaining moles of I2 from the starting moles of I2 ?
The remaining I2 reacted with thiosulfate not with SO2!
ONLY 0.001 moles reacted with SO2 and the remaining I2 reacted with thiosulfate.
So shouldn't the number of moles be 0.001 moles?

Chem98
8. Let's pretend that you started with 10 mol of I2.

You react those 10 mol with an unknown amount of SO2.

The remaining I2 reacted with S2O32-.

You find, by calculation, that there must have been 4 mol of I2 that reacted with your S2O32-.

Where did the rest of the I2 go? It reacted with the SO2! How much I2 reacted with the SO2? 10-4=6 mol
9. What Pigster said, your finding the difference.

Alex
10. (Original post by ajsullivan)

Attached is a work through of the answers. I hope this helps (pretty much what Pigster was eluding to, so thought I would finish it off as a worked example). If you need any revision notes or questions/model answers etc. check out my 100% free website www.scienceskool.co.uk

Have fun

Alex

Hi ajsullivan,

Sorry to bother you, but why can starch be used as an indicator for this titration (part a)?

Thanks,

Jasmine
11. The titration involves the conversion of I2 into I-.

I2 forms a blue-black solution in the presence of starch whereas I- is colourless.
12. (Original post by Pigster)
The titration involves the conversion of I2 into I-.

I2 forms a blue-black solution in the presence of starch whereas I- is colourless.
Thank you Pigster! I understand now!

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