Re: Why does salt dissolve in boiling water and flour does not?

It all has to do with what each thing is made of. Salt is made of two simple elements - sodium and chlorine. they combine to make the salt molecule, which is very small. This molecule is very simple and can dissolve very easily in water.

Flour is a very complex, large substance, made up of many complex molecules, including protein, starch - which is carbohydrate - and a few other things. When starch is put into boiling water, it absorbs water and begins to swell. It will continue to swell until it is so full that it will burst. Some of the pieces of swollen starch will join together to make clumps - your dumplings. This is the whole idea behind making gravy or a similar sauce. You add water to a starch - cornstarch, flour, etc. - and heat it, stirring all the time so that when the starch molecules break they don't clump back together - making lumpy gravy - but stay suspended in the water. An interesting experiment is to use several different kinds of starch and see what they will be like after boiling. Some will be cloudy, others will be clear, some will make a very thick paste while others will be thinner. You might suggest this to your teacher.

Thanks for a good question.

Jill Irvin
Ohio State University