(chem) prove pure water

the answer above is a correct throem,but pls think that ,ther may be some pullutant,in the beaker or condensation tube, so the distillate may not be pure.
Well, i cannot say you are wrong ,but even pure distillate ,its boiling point may not be exactly 100 degree cesius(wrong spelling) ,i have use Bunsen burner to heat pure water until it boiledbut the temperature of boil water is94degree cesius(wrong spelling).In my way, i will evpourate the distillate, since pure water must not contain any soluble and insoluble substance.For insoluble substantce, you can look it by your
eye(s).But for soluble substance, you can use evpouration to evpourate water by using a water bath,wahen all water have evpourate, get the watch glass down form the water bath, look at the watch glas ,if there is no any soild or powder,the water is pure.
I'm only a F.4 student,if i have wrong ,pls tell me, thx

2012-04-24 18:09:06 補充：
Well, the freezing pt of pure water is not 0 degree cesius, if i have remeber wrongly, the freezing pt is -4or even lower(??) degree cesius

To what extent should it be pure water? "Pure" has many levels which leads to different complexity in the analyses.

This may be a bit difficult
But, one of the ways may be by using boiling point and melting point.

For a pure substance, they would have a sharp melting point or a sharp boiling point.
First, during the distillation, measure the temperature of the steam. If the steam is 100 degree sharp, and remain constant

We may should (not really 100% sure actually) the solution mainly contains water or say it is pure water

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