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health advisory Hospital Doctor Yu 2007-11-8 19:09:04

Answers:

I personally love this one.

When my students finish a sodium hydroxide titration, they fail to realize that eventually the indicator will change back. Here is why.

The atmosphere contains an inherant amount of acid. This acid reacts with the NaOH and thereby changes the normality.

Here is something fun to do to new Chemistry students. Let them titrate until phenolthalein is slightly pink. Then huff a breath into the flask. It goes clear. You ought to see them freak!

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If it is personally changed, that is to reach the desired PH number, for a certain chemical reaction.

and if it changed on its own, then because it was kept in a non-pvc bottles or jars, which permitted air to hydrate the NaOH which will lower its normality.

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Sodium Hydroxide solution combines with carbon dioxide in water (carbonic acid), to form sodium carbonate and sodium bicarbonate. To slow this process, use freshly - boiled water, and keep the container sealed, after you make the solution.

Many people do not realise that distilled water has a pH of about 5, if it is allowed to equilibrate with the atmosphere, because of dissolved carbon dioxide.

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