Imidazole is sometimes used as a buffer because it is cheap, reasonably benign,

Question

Imidazole is sometimes used as a buffer because it is cheap, reasonably benign, and has a pk of 7.0. The acid form of imidazole can be added as the chloride salt with a molecular weight (mw) of 104.5. The neutral basic form of imidazole has a mw of 68.1. How much of each form would you weigh out to make 1 liter of a 200mM solution at pH 7?

Explanation / Answer

200mM=0.2 M solution. 0.2M= 0.2 mol/L For 1 litre we need: 0.2 mol/L*1L=0.2 moles of imidazole no.of moles=mass in g/mw Rearrange that--> mass in g= n*mw For chloride salt form: mass= 0.2*104.5= 20.9 grams need to be added to make 1 L of 200mM solution. For neutral form: mass=0.2*68.1=13.62 grams need to be added to make 1 L of 200mM solution.

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