Attention all chemists!

[aka estie]

A lowly biologist is in need of your help!

I am making bacterial Minimal Basal Salts media, which calls for a solution of 0.4g SnCl X 2H2O in 100ml of DI water.

I have attempted this solution twice, and no matter what I do, it stays very cloudy and will not completely dissolve. I have tried stirring with heat, and have added small amounts of 10% HCl as well.

Any ideas how I can get this into solution??

[aka estie]

I don't know why, but adding NaOH and then HCl seems to have done the trick!?!?

Adding HCl alone didn't work!

Any explanations for that????????

[Hamish]

Hi, what is this for? It sounds a little unpleasent! I assume SnCl is SnCl2 ?. Can you give the exact amount of material you are adding and the conc of H2O2 you are using? Sounds like you are making SnO/SnO2 .... too much peroxide?

[JustSia]

Hamish, not a chemist myself but I believe SnClx2H20 is a water complex and not the separate compounds. I am sorry aka estie I can't answer your question. From out here it seems pretty straight forward 0.4g of complex dissolved in 100ml of DI water so couldn't possibly tell what is going wrong.

So unless there is someone here who knows this I suggest you first make sure there were no mistakes in the actual directions and then speak to your tutor (I would imagine you have one)

S.

[shammydodger]

Aka estie

Presumably you are using tin(II) chloride dihydrate?

Did you begin by dumping all the salt in the total volume of water, or did you start with a small amount of water and then dilute the solution? The problem lies in the fact that tin(II) chloride will readily dissolve in small quantities of water, but as this initial solution is diluted the tin(II) chloride hydrolyses to form an insoluble basic salt:

SnCl2 (aq) + H2O (l) === Sn(OH)Cl (s) + HCl (aq)

This is an equilibrium process, so adding hydrochloric acid to the solution is required to shift the equilibrium to the left and thereby prevent, or at least limit, the hydrolysis and keep the solution clear.

I'm not sure why you were having difficulty even when adding HCl. Maybe you weren't adding enough.

[theprof]

I haven't got all the answers for you but I can account for the cloudiness your observing in solution.

Stannous Chloride over time absorbs oxygen from the air to form insoluble Stannous Oxychloride, which forms a white suspension in water.

This is most noticeable if old or impure Stannous Chloride is used. Old Stannous Chloride has had the time to absorb the oxygen, whereas technical and "pure" grades often contain it as an impurity before you start.

Just to check the obvious, it was "Analar" grade or equivalent Stannous Chloride you were using? How fresh was the batch?

Shammydodger is quite correct about this and it looks like we've been thinking along the same lines. All the same, go back a step and check your Stannous Chloride.

[Hamish]

Got my twos in the wrong place! sorry

[aka estie]

I just spent 5 minutes writing a long answer, and it disappeared! Argh!

Anyway, what I tried to say was thanks to everyone for your help.

I tried again this morning and used a lot of 10% HCl (almost 2ml) until it cleared.

I mistyped in my question. I did indeed use SnCl2. The recipe said SnCl, but I assumed it was a typo too. The bottle we have is reagent grade Tin(II) chloride dihydrate (98%). And it is fairly new (5 months old).

Anyway, I hope it all stays in solution now!

Thanks again everyone!