[happycamper]

Hi all,

This isn't homework. I'm an ecology teacher and someone in my lab ordered Sodium Thiosulfate at .0250 N, but the dissolved oxygen kits we have use .0109 N. It's been a while since I've been in chemistry. How do I figure out how much water to add to the .0250 N solution to make it .0109 N, if indeed that is the way to do it?

We could send it back, but it won't get here in time for our next few groups coming in.

Thanks for helping!

[Archer]

I wish they would use Molar it would make things a little easier.

Anyway, as the application you are using this for oxidises the molecule and it can only oxidise once I am assuming that 1N = 1M. It doesn't change the end result so it won't matter when someone corrects me but it makes the calculation easier to follow through if we work in Molar concentration (mols dm^-3) as I said the units are irrelavent because you are simply diluting.

So at 0.025 M you have 0.025 mols of sodium thiosulfate in every litre of solution, or 0.025 mmols in every ml

1 x 0.025 = ? x 0.0109

? = 0.025/0.0109

? = 2.29

So dilute your solution up to 2.29 ml for every 1 ml of your stronger solution and you will have a 0.0109 N solution.

So depending on what volume you have and need you need to dilute to approximate 2.3 x the volume.

[happycamper]

Thank you very much.