Australia's Science Forum

Hello again "Brains Trust"
In the back of my mind, I half remember being told earlier this year that we are no longer allowed to do the Potassium Iodide plus Lead Nitrate to produce Lead Iodide precipitate experiment. Is this actually the case, or did I imagine it? Risk Assess does not seem to think it is a problem. If it IS the case, can somebody point me to "Chapter and verse" where I can find this information. I have a staff member wanting to do this one tomorrow. We have always done it, so I will need something pretty authoritative if I need to ban it now when it has been a staple reaction.
Any advice appreciated!
Cheers
Ian

Lead nitrate just needs to be a very low concentration. Check Riskassess for the concentration suitable for Yr 7-12. It does still produce a precipitate.

Hi Ian, I really do not think it is banned. Just use your common sense, we all know you are great, its the others that often need extra help. We use dropper bottles think that is the way to go,

Thanks for your vote of confidence, Labbie.

I guess, my concern is that they keep changing the rules! I don't want to be guilty of telling people the wrong thing, but there is a lot of "Hearsay" that may make sense, but if it is different from what "has always been done" then people want more than just my word before they will change. When I was young, reducing mercury from mercuric oxide with a blow torch was a common year 8 experiment! Copper sulphate was that harmless chemical that was in every toy shop "Chemistry set". I still get conflicting reports about whether Manganese Dioxide is OK to use or not! (similarly, Borax, etc, etc)
Anyway, hopefully that explains my caution!
Good to chat to you again, Labbie!

Cheers
Ian

Hi Ian,
I did a search here for comments about lead nitrate 0.1M and RiskAssess has it teacher only. Phillip Crisp suggested making note on your risk assessment that the teacher has assessed the chemical as per D of E CSIS standard current at the time. It at least shows the chemical was assessed even though it seems in conflict with RiskAssess. Hope this makes sense.

I have not heard of it being Banned Ian .
Although CCIS has 0.1M Lead Nitrate as 11-12
7-12 is 0.05M .Our Chem teacher always complains about it being too weak and not working as he thinks it should .

From Science Assist

Lead nitrate in solution is included on the List of Recommended Chemicals in order that the reaction of lead nitrate and potassium iodide to give a yellow precipitate of lead iodide may be conducted. This reaction gives a dramatic colour change and is effective on a microscopic scale; using one drop each of the reactants on a white tile, spotting tile or flat acrylic sheet. Making a precipitate in a test tube is not recommended because of the difficulty in cleaning up the only very slightly soluble lead iodide. A teacher demonstration of this reaction is also a good alternative.

This is from Sydney Catholic Schools -

Can schools keep using lead nitrate?

The use of lead nitrate has not been banned in Sydney Catholic Schools. Lead nitrate was reclassified as per the Globally Harmonised System for classifying chemical substances. This reclassification only changed who can use the stronger concentrations of lead nitrate in schools. The following guidelines have been taken from RiskAssess and should be followed when using lead nitrate solutions:

•Solutions above 0.03M should be restricted to teacher use only


•Solutions between 0.03M and 0.003M should be restricted to students in years 11 & 12 only


•Solutions below 0.003M are suitable for students in years 7 - 12 with appropriate controls


To help reduce potential exposure, it is essential that teachers ensure that teachers/students use micro techniques when doing pracs relating to the solubility rules. Paddle pop sticks soaked in lead solutions should also be used for flame tests to minimise over-spray and the cleaning of benches. The use of crucibles (in fume cupboards) is an acceptable practice in science as well

Lead nitrate solutions will be reassessed when the new Chemical Safety in Schools Guidelines are released. The above guidelines are currently at a higher standard to past practices used in schools and will provide our schools with the best handling practices.

It's a bit of a problem when the curriculum calls for 1M in Yr 12 Chemistry

Thanks, All for all the feed back.

I have made up a batch of 0.003M Pb(No3)2 for the teacher who wanted it, and have diluted all my dropper bottles of 0.1M down to 0.003M and re-labeled them.

She is actually doing a Conservation of Mass experiment from "Science by Doing" resource. I end up with 16 conical flasks with PbI2 to clean up without getting any on myself! Something to look forward to!

I doubt that she will be using "Micro techniques", Smee, as she needs enough of each reactant to measure the weight of it!

Cheers
Ian

Conservation of Mass - Pearson textbooks Y9 & Y10
Y9 - uses 0.1M solutions of NaOH, CuSO4, sodium carbonate and ammonia.
Y10 - uses solutions of barium nitrate and sodium sulphate.
So far it works.

Thanks Lyn.

We don't have Pearson Science at out school, but my daughter has access through her school to the on-line versions. do you know what chapter sections I would find those pracs in?

Cheers
Ian

Thanks again Lyn. I found it!
cheers
Ian

Hi Ian
I asked the Science Assist folks this question last year and they have advised me that the use of 0.01M lead nitrate is okay. We use that concentration here and all works well. If you go to the Science Assist website you'll be able to find the answers to your question there is alot of information available there.
Cheers
Krysia