Practical investigations
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Why is sodium hydroxide not a primary standard in titrations?
Solid sodium hydroxide absorbs water quite quickly when exposed to air - it is hygroscopic. When you try to weigh it accurately, you will find that its mass slowly increases with time. The solid starts to glisten with moisture after a short while.
Sodium hydroxide also reacts with carbon dioxide in the air, to form sodium carbonate. Thus it is difficult to obtain pure, and once made up, the solutions still absorb carbon dioxide. This can interfere with the endpoint in a titration.
You may have noticed the white crust of sodium carbonate around the stoppers of some bottles of sodium hydroxide solution in your school labs.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 01 December 2006
