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#1 Quirkycat

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Posted 13 January 2005 - 11:36 PM

Please, can anyone help me with this question? I really don't know what to do and it's due in tomorrow, and I tried looking on the BBC website but I don't understand it at ALL, so any help would be really appreciated! Thanks!


'' Taking the volume of sodium thiosulphate solution to be 22.45 cm3, calculate the volume of ozone in ONE LITRE of air ...
(take the molar volume of ozone to be 24 litres mol-1)

These two equations came with it;

2KI + O3 + H2O ---> I2 + O2 + 2KOH

I2 + 2(S2O3)2- ---> 2I- + (S4O6) 2-

any help at all? Even if you can tell me how to do this style of question?

Edited by ally, 14 January 2005 - 06:55 PM.

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#2 Dave

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Posted 14 January 2005 - 06:09 PM

i have forgotten most of Chemistry but as for formatting equations you can use the "BB code help link under the smilies" this will show you how to use sub-script and super-script i would edit it for you myself but i am not the mod for Chem maybe ally will do it if he gets their before you smile.gif

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#3 Quirkycat

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Posted 16 January 2005 - 04:50 PM

QUOTE(Dave @ Jan 14 2005, 06:09 PM)
i have forgotten most of Chemistry but as for formatting equations you can use the "BB code help link under the smilies" this will show you how to use sub-script and super-script i would edit it for you myself but i am not the mod for Chem maybe ally will do it if he gets their before you smile.gif

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K, thanks!!
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#4 George

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Posted 16 January 2005 - 05:42 PM

Sorry this reply is too late for you, but hopefully it will still help for the exam smile.gif

Firstly, if you are having problems with all the sorts of questions involving moles, you should approach your teacher for help - I'm sure they'd be happy to go through it with you.

I'd also recommend the notes on this site tongue.gif HSN11200 - Topic 2 - Enthalpy Changes/The Mole is probably the most relevant, but you might find the other Higher Chemistry resources useful too.

In the file I've linked to above, you'll find lots of examples of mole-based calculations. It's all summarised in a diagram on the last page - basically, every question is asking you to use those relationships to get the answer.

The method used in the notes is proportion, which requires you to think a bit. I was taught to do the questions that way, and it works for me smile.gif Other teachers use formulae for that sort of thing, and I'm sure there are other members here who can help you with those if you want.

I've not done chemistry in a while, so I might be wrong, but these are the steps I think you need to go through in this question:
  1. Find the number of moles of sodium thiosulphate in the second equation. You must have it's concentration, because I can't think how you would do it otherwise blink.gif
  2. The number of moles I2 reacting with the thiosulphate is 1/2 the number of moles thiosulphate
  3. This number of moles I2 must have been produced in the first equation, and the number of moles O3 is therefore the same
  4. Using the molar volume given, you can find the volume of ozone

I hope that's helpful smile.gif

#5 Ally

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Posted 17 January 2005 - 11:45 AM

Which past paper is this from and can you check whether the equations are right?

#6 Quirkycat

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Posted 30 May 2005 - 08:44 PM

Wow ... thanks guys ... soz I didn't check back on this post sooner! It was some ancient past paper we did (honestly? What's the point in doing Chemi papers from fifteen years back? The style of questions will have changed totally!) so I'm not too worried about my crappy D in it tongue.gif

Hopefully the exam will go a lot better, lol!

P.S. Yeah, I should have asked my teach ... but she's a real gorgon so I asked my dad instead!

But thanks again for the help! smile.gif
LOL ... it's me again! *grabs ppl to stop them running away* Now just u stay and listen to me ... hehe!





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