The Student Room Group
Reply 1
and can someone tell me what the equation would be for nitric acid reacting with sodium thiosulphate? thanks
sodium thiosulphate is decomposed by the H+ ions in all dilute acids to give a yellow/white precipitate of sulphur.

It is, in fact, a disproportionation reaction with the sulphur atoms in the thiosulphate ion being both oxidised and reduced...

S2O3(2-) + 2H+ --> SO2 + S + H2O
Reply 3
Also, if i have 1M solution of sodium thiosulphate and I measure out 2cm3 of the sodium thiosulphate plus 8cm3 of water and mix the two together, how do i calculate the molarity of the 10cm3 solution??
work out the number of moles of sodium thioslphate in the solution that you add and then divide this by the total volume of the new solution.

Molarity always equals moles/volume

BUT if you are confident in maths you can work it out using simple ratios. You are multiplying the volume by a factor of five therefore you should divide the molarity by a factor of five to get the new concentration.

2cm3 of 1M made up to 10 cm3 is a five-fold dilution therefore the new molarity = 1/5 = 0.2M
Reply 5
I understand how to do it the ratio way but u can't seem to be able to get a molarity of 0.2M when i use the equation molarity = moles / volume?

i dont have the mass of the thiosulphate :s do i just use the 2cm3 and convert that into grams? because when i do this i get the molarity as being 1.2M but this can't be correct because the molarity of the thiosulphate solution is 1M?
no, you just say:

1M sodium thiosulphate contains 1 mole per litre

therefore 2cm3 contains 2/1000 x 1 moles =0.002 moles

now put this into 10cm3 = 0.01 litres

molarity = moles/litres = 0.002/0.01 = 0.2M
Reply 7
ohhh i see. thanks for your help!!
Hi there,The following products will be formed - sodium sulphate- water- Nitrogen dioxide- sulfurThe solution turns to milky
Reply 9
Original post by natashadominic7
Hi there,The following products will be formed - sodium sulphate- water- Nitrogen dioxide- sulfurThe solution turns to milky

Please, before you reply to a thread, just have a check that is isn't 12 years old.

I suspect that *mini* won't see your reply. What with them having left university about 9 years ago, have found a partner, have two kids, a job, house, two cars and a family holiday in Corfu planned for later this year.

I fact, what is the chance that anyone in this thread is still on TSR?

Oh!