I am completing the post lab analysis for a lab where we tested 3 different solu

Question

I am completing the post lab analysis for a lab where we tested 3 different solutions in a spectrophotometer that consisted of 5 mL of 6.75 pH buffer solution and bromothymol blue indidcator, mixed with 1) 1 mL of 1 M HCl, 2) 1 mL of 1 M NaOH, and 3) 1 mL water in order to calculate the absorbance (to eventually lead to the calculation of pKa and Ka). The question says: "From the pH of the buffer solution given, calculate the concentration of acid, [H3O+], for the green solution. Keep in mind that you added water to the buffer solution when you prepared this sample." How do I go about this? The green solution refers to the buffer and water solution.

Explanation / Answer

Green colour solution refers to indicator+buffer+water as per the given data..and buffer pH is 6.75

There fore according to the pH formula pH= - log(h+) and so

[H+]=10-pH

=10-6.75

=1.77×10-7

Therefore for green colour solution the concentration of [H+]=[H30+]=1.77×10-7

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