O Level Chemistry: School Practical / SPA Tips

Halo students and avid readers,

This is one of the latest question sent in on Chemistry Practical. It’s a good question which I think some students would love to find out the answers as well, isn’t it? 😉

“I wanted to ask what’s the correct/appropriate way to wash test tubes when you’re having a Chemistry practical? Because i’ve faced shortage of time, and it’s because i wasted a lot of time to wash my test tubes. Some students maybe more “kiasu” and they washed the test tubes multiple times to ensure it’s clean.

For example, i’ve 6 test tubes, but i’m required to do 7 or 8 experiments, so i’ve got to wash the test tubes. However, the test tube i’m re-using again, may have traces of the previous solution left and thus, affecting the result of the current one. Please do advise me on the correct and advisable method to wash my test tubes!

Is it okay to wash my test tube just with plain tap water or distilled water? Or both? And i do believe most schools provide a brush, which can fit into the test tube to remove solid particles or ppt which hardens and stays in the test tubes, am i required to use it, or it can be ignored?

This is approximately how i wash my test tube

1. I empty the solution into the sink
2. I rinse the test tube with tap water first
3. Then, i rinsed it again with distilled water.”

Let me sum it up with the most comprehensive & time effective method that i have came up with several teachers:

During Volumetric Analysis and Qualitative Analysis, what we are testing on are essentially the reactions between ions, i.e. Cations and Anions. And this is a very important clue on how we should conduct the practical.

I would suggest the following steps if you need to wash the test-tubes cos u need to re-use:
1) Choose the test-tube that contains only solution (colored or colorless).
2) Pour the content into the sink.
3) Wash once with distlled water.
4) Use brush to scrup few quick times.
5) Use distilled water to wash tubes thoroughly with two more washings.
6) Ready for next test.

PS: Tap water should not be used as they contains Ions, and those ions present might interfere with your results. Distilled water has less of such problems.

PPS: Soap should not be used cos generally they are alkaline and contains the anion OH- hydroxide ions, which might interfere with results.

PPPS: Choose a tube that contains solution instead of one that contains PPT. This will prevent waste of time in washing tubes.

Hope you will find this information useful.

Rgds
Sean =)

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