Australia's Science Forum

Hi All,

I went into the chem store room to do an end of year check and noticed that the sodium hydroxide solutions (various strengths) had a white crystal growth around the tops of some of them. First thought was sodium salt (chloride?) crystals after the solution must have reacted in some way with the humidity in the air and or if they were made up with town water rather than distilled water (hence the chlorine)
I had been job sharing until recently so not sure how these solutions were made up??

After some ideas about what to do, pretty please.

Could it just be sodium hydroxide?

Just wipe the white stuff away from the neck of the bottle with a damp cloth or if the plastic dropper lids are clogged take the lid off open it up and run tap water through to get rid of residue and dry lid before replacing on bottle. With the plastic dropper bottles check to make sure there are no cracks in the plastic bottle. Depending on what the chemical is, the bottles can become brittle after a while. The plastic tops can also become broken (cracked) and need to be replaced. I have just been through the dropper bottles and replaced a number of lids, disposed of a few cracked bottles. Remove labels rinse and chuck in garbage bin. A few of the chemicals can do this apart from sodium hydroxide, ie copper sulfate, copper chloride, magnesium sulfate (just found that lot as well as more split lids on the lead nitrate bottles). Some chemicals just don't want to stay put in the bottles. I wouldn't worry about it too much. It just becomes some extra tidying up to do. If you wipe the residue off now it is likely to be back by the beginning of next term and then you will repeat the same procedure again.

Thank you Lyn and Merilyn. There was a fair bit of it accumulated there and I hadn't noticed it before. I wasn't sure about handling it?
I've attached a picture. I hadn't noticed it before today but I'm not in the habit of going into the chem storeroom if I don't have to.

That happened to us too with sodium hydroxide and HCl, both quite strong concentrations around 8M. I just did as suggested. Had a cloth with water and wiped it away. This was last term and I went to the chemstore and saw it's started to recrystalise again. Continuing jobs....

Sodium hydroxide slowly reacts with glass to form sodium silicate, so glass joints and stopcocks exposed to NaOH have a tendency to "freeze". Flasks and glass-lined chemical reactors are damaged by long exposure to hot sodium hydroxide, and the glass becomes frosted. It should have a plastic lid. NOT GLASS

Sodium hydroxide stock solutions should be stored in plastic containers. Glass containers should be completely avoided in the preparation and storage of sodium hydroxide solutions.

Kassh see how the plastic lids are fine but the glass one is not. Removed the glass one and go for a plastic lid.

KassH wrote: ↑08 Dec 2022, 11:56 Thank you Lyn and Merilyn. There was a fair bit of it accumulated there and I hadn't noticed it before. I wasn't sure about handling it?
I've attached a picture. I hadn't noticed it before today but I'm not in the habit of going into the chem storeroom if I don't have to.

Goodness what a mess. I suggest throwing away every old style chemical bottle like that. You will still get the build up on other plastic bottles but you are less likely to have lids freeze shut on you. As others have said store in plastic and don't be to concerned....throw away the glass bottles though. I have collected them over the years and they are displayed on my bathroom window, I have lots of amber ones too of all sizes, lovely. No place for them anymore in a modern lab

Thanks everyone. We have soooo many of the glass ones. Will clean it up as suggested, put plastic stoppers in and put a change to plastic bottles on the list for next year! Running out of time in 2022!! One week to go and teachers still have pracs running AARRGGGGHHHH!

I still use glass ones as plastic will perish with things like vinegar. Most of the non caustic things seem to be alright in glass, and they are easier to keep clean. Tops free up with hot water. The white stuff around the caustic chemicals is caustic, so use PPE when you are cleaning it.

A smear of Silicone grease on the tapered lids usually stops this happening .It lso stops the lids fusing on .

Is it safe to rinse the droppers in 1mol hcl to clean out the NaOH, and still use them in the NaOH. I think that they might be some wax in the droppers and bottles, i have tried washing in water to no avail

NicD wrote: ↑03 Nov 2023, 07:54 Is it safe to rinse the droppers in 1mol hcl to clean out the NaOH, and still use them in the NaOH. I think that they might be some wax in the droppers and bottles, i have tried washing in water to no avail

Yep, go for it

thanks