Australia's Science Forum

Hi Labbies,
Can anyone suggest a good cleaning solution for test tubes with stain from corrosion pracs?

Thanks a lot.
Cheers,
Ana

Hi Ana,

I use CLR. I buy it from Coles,let it soak then use a test tube brush to clean them.

Jodye

Yes, but you must NOT laugh Nappy san, its really great. Learnt that one on the great site. For rust stains try fresh Oxalic acid.

Right on Labbie! Nappi-San every time.

I think I will give napi-san a try..the CLR is a bit smelly!

A tip for the future

I have a large supply of specimin jars ( like what you get to provide a specimin at pathology) they get used over and over again for the corrosion pracs, they have some residual staining but it doesn't matter. Saves trying to get the stains out of test tubes and stops test tubes being tied up whilst the stuff is corroding.

Wendy

Sodium metabisulfite or oxalic acid, rust and potassium permanganate stains. No or very little scrubbing involved. Soak for few hours and rinse.

Again, thank you so much for all suggestions. Will try which ones work quickly.

Have a great week ahead!

I fill each test tube to the required level with 2m HCl and leave over night. (standing in a beaker). Rinse off next day, don't usually need to brush.

I'm with dime I use HCL works everytime leave overnigt and wash.
Also Sodium Hydroxide for the burnt sugar prac gets them clear if you soak over night.

I have found that nothing works on our test tubes for rust stains. Have tried the hydrochloric acid, napisan, oxalic acid... I just can't seem to win! maybe I will try again this year and see what happens.

I find HCl works well getting rid of rust stains - just fill the tube to just above the stain with 4 - 6M HCl and leave for a couple of days in the fume cupboard (with a corrosive sign!!). Then wash as usual. I resuse the acid time and time again and it works every time! Have had the same bottle for years.

Well I must be the laziest labbie around.
We do the rusting prac in 10ml culture tubes that I buy in bulk and work out at 7cents each. I dont even bother trying to wash them at that price, straight in the bin they go. I figure the time, water, cleaning chemicals just doesnt justify washing them. I have better things to do with my time lol,

My latest take on the rust experiment is to buy sleeves of 100 x 30mL sauce cups from our local Star Packaging company, with lids, and the little cherubs get little squares of steel wool to put in them. It's a win/win/win for us all.
1) The steel wool rusts better than nails
2) The set-ups don't occupy test-tube racks for days
3) The little containers can just get chucked out at the end of the experiment
4) At approx $6.50 for 100, it's really cheap.

Great idea, Smiley! Do you have a galvanised alternative? Our kids do water, oil, air, water (nail completely submerged) with oil on the surface (I think?) and galvanised.

We don't do a galvanized alternative. However we do this as a two-stage experiment. Stage one is water, slat water & air. Stage 2 is where the cherubs have to design their own experiment, with a limited range of gear - e.g. oil, boiled water (to remove air), varying strengths of salt water etc. We do offer to place other metals in the cups as a form of sacrificial anode (although we don't use that terminology with tinies). We are following the National Curriculum and frankly, I just do what I'm told. However, one could always just chuck in a tiny galvanized nail, and compare I guess.

Ah yes - boiled water with oil on top to stop gas exchange! That's the one I was thinking of. And I think they do salt water as well. Definitely will be promoting this idea to the teachers!!!

I have a bucket of HCl for cleaning of glasswear. I wait till i have a bit that needs doing and I soak it over night. Works every time.

Good luck.

KIMMY

Re rust pracs -Bi-carb soln prevents rust. I've had a prac going since 2005 and while some of the testtubes with water, salt etc and nails are completely rusted to soup the bicarb just keeps on giving. I just top it up every so often. Gets 'em thinking.

I just keep all the rust effected test tubes set aside for next year