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When you usually collect gas in a tube the first gas collected is often rejected. Why is that?
141108

Corrie writes ....
 
This is because the first amount of gas collected is likely to contain some of the air present in the apparatus before the gas you want was generated. We usually talk of 'displacing the air from the apparatus' before collecting the reasonably pure (we hope) sample of the gas being investigated.

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: 16 November 2008

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