Chemical quantities (AS)
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How do I find a “standard” acid solution to use for an acid-base titration. The aim of the titration is to find out the concentration of sodium hydroxide in solutions of unknown concentrations. Also which indicator would it be best to use to find the end point?
Igloo writes
What you need is a 'primary standard' that you can obtain pure, weigh out accurately and then dissolve quantitatively in water and make up to a definite volume in a standard flask.
The usual acid chosen for this purpose is potassium hydrogenphthalate. This may seem to be a rather obscure substance, but it is a solid at room temperature, and able to be obtained in a high state of purity.
If your school/college doesn’t stock this solid, perhaps you could persuade your teacher to obtain some. It’s fairly easily obtained from suppliers and isn’t particularly expensive or hazardous to handle. It’s a monobasic acid, so one mole of it will neutralize one mole of sodium hydroxide. The indicator to use is phenolphthalein.
Always carry out a risk assessment before starting practical work, and check with your teacher.
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: 11 November 2004
