Practical investigations
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Hi, I'm doing my A2 aspirin investigation where a known excess of base (NaOH) is added to the aspirin and the excess is back-titrated with a standard solution of HCl. I need to standardize 0.1M NaOH with potassium hydrogenphthalate, but I don't have any idea how to do it! I've looked through all the FAQ's on your website but haven't found anything helpful, please help!
Corrie writes ....
Potassium hydrogenphthalate (KH(C8H4O4)) is a stable, crystalline solid that can be obtained in a very pure state and therefore weighed out very accurately to make up 'standard' solutions. These solutions can then be titrated against alkalis (1 mole of KHP reacts with 1 mole of OH- ions).
So, make an approximately 0.1 M solution of KHP using a suitable volumetric flask and work out its accurate concentration from the mass used and the volume of the solution. Then use this solution to titrate against your NaOH solution, using a suitable indicator, to find the accurate concentration of the alkali.
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: 09 September 2007
