Practical investigations
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I am trying to find out the order of the reaction between hydrochloric acid and Mg, by measuring the rate at which hydrogen is produced. I have found that the test-tube gets very hot during the reaction,
therefore I am going to carry out the reaction in a waterbath - to ensure that the temperature remains constant.
Should the water be cold or at room temperature (about 20 oC)?
Corrie writes ....
Unless you have efficient stirring to distribute the heat generated to the cooling water around the test-tube, I doubt just putting the test-tube into a waterbath will help much. If you use a side-arm test-tube, you could include a thermometer in the top to monitor the temperature of the mixture and see how significant the temperature rise is.
Consider other methods of reducing the temperature rise, like a greater volume of acid (in excess anyway in your experiment, so adding more will not change the rate?) or a small conical flask instead of a test-tube to do the reaction in - this will enable you to swirl/shake the solution more effectively to distribute the heat.
I don't think it matters which temperature you have waterbath at - it's more important that whatever temperature you choose, the temperature of the reaction mixture is kept as near constant as possible. Consider what you think would be an acceptable temperature rise to allow.
Do not rely on what is said here. Always carry out a risk assessment and check with your teacher before starting any practical work.
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: 12 November 2007
