Australia's Science Forum

My two young ladies have asked, if their traineer has told them a old way or not.

I do both..it depends on the solubility of the solid you are trying to dissolve. If it is highly soluble, add water to the solid. If it isn't as soluble, you may form larger lumps that become very difficult to fully dissolve.

Depends on what I am mixing - no set rule for all chemicals.

I think for a new labbie as bad as this is it is alot of trial and error. Most of us have been thrown in the deep end at one stage and all manage to come out - maybe a few extra wrinkles but always smiling.

Just remember there are worse jobs in the school.

KIMMY

Usually I add water to the solid, mainly for convenience because then you weigh the solid in the beaker and add water, one beaker = less washing up.

However, for acid you must always add the acid to the water.

Also, for some solids when you add water they get really hot or really cold so when mixing those ones I generally add the solid to the large amount of water to avoid burns (if I remember!!!).

Wa-a-a-ay back last century when I did a Lab TECHNICIAN'S Certificate, we were taught to always add solid to SOME distilled water and mix, then make up to the correct volume. I still do this, especially when I'm busy, and using a magnetic stirrer. I weigh out the solid, chuck it in a beaker or a flask with about 1/2 the required H2O, then let it stir while I get a volumetric flask ready/take a phone call/answer the prep room door/split an atom...whatever.

It all depends on what it is... I often use a small amount of cold distilled/demineralised water to make a paste of the chemical in a large beaker, then boil distilled water in the electric jug and stir it into the paste - often the chemical dissolves immediately.