Questions & Answers

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Question about acetate buffer and what happens when HCl is added to such a solution

Debra ask: How do I attack this problem?
I want to compare the effect of adding 1mmol of HCL to 100 ml of 0.2M acetate buffer at two different starting pH's.
(pKa of acetate buffer =4.7 Initial pH = 4.7 Initial pH = 5.7 Thank you

Hi Debra,

There is both a short and long answer to your question. The short answer is that at pH=4.7 you are much closer to the equivalence point of your buffer (pH 4.7 when its a CH₃COOH <==> CH₃COO^- buffer) and at that pH the addition of HCl will cause a much larger change in pH than at pH=5.7.

However, you can calculate (this is the long answer) how much pH changes by doing some fairly simple calculations. Since the explanation is not short I've made a separate webpage answering your question. It is named acetate buffer. The answer is also found as a pdf document named acetate buffer. The Excel spreadsheet showing all the calculations is shown here.

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Question about glucose and ionic strength

Anonymous ask: what would be the ionic strenth of say 100mM Glucose? where there is no charge?

Dear Anonymous,

When there is no charge there is no contribution to the ionic strength. Ionic strength only counts charge ions. So, for any standard calculation glucose is not considered charged - and do not contribute to the overall ionic strength of the solution. You can refer to the page about ionic strength.

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