I don\'t even know where to start with this. How do you determine hydrogen ion c

Question

I don't even know where to start with this. How do you determine hydrogen ion concentration in a buffered solution? which available weak acid and conjugate base would be best for this reaction and why?

During an esperiment a few weeks ago, you looked st the effect of hydrogen peroside concentration on rate for the 2 reaction below and included the potential effects of H and I into the rate constant by keeping these concentrations constant. Design an esperiment (ot set of esperimesta) to investigate the effect of hydrogen ion concentration on the rate of the same reaction In this esperiment, there are three competing reactions (isted below), We will be looking at the rate of reaction 2 Reaction 1 (vitamin C & iodine redox reaction) . Fautet Reaction 2 (Godide ion & hydrogen peroside redos reaction)-Slau Reaction 3 (starch & iodine)- Fast L-+ starch starch-1 Other pieces of information Available weak acids and conjugate bases are: acetic acid, potassium acetate, sodium acetate, sodium bicarbonate, sodium carbonate, citric acid, benzoic acid, boric acid, phosphonc acid, sodium hydrogen phosphate . If your buffer is also an oxidizer like hydrogen peroxide), you may have an unwanted side reaction in that the sodide may be oxidized by your buffer rather than the hydrogen peroxide

Explanation / Answer

I can see that this is not a general calculative question rather this one requires strong basics and crystal clear concepts of the chapter.

To start working on the question, we can start by looking at the the three reactions. see that the first and the third reactions are fast as compared to the second one, so those two will be near completion as soon as we start of the reactions. Since we are taking into consideration the effect of the concerntration of H+ , in order to cause noticable changes in the rate of reaction, we should take two electrolytes, one which gives too much of H+ ions and the other one which will give too less H+ ions. Also it should not be having any reducible species as it will result in oxidation of iodide.

There are various formulas to calculate the concerntration of H+ in buffer solution for example

pH = pKa + log10([A-]/[HA]), where Ka is the "dissociation constant" for the weak acid, [A-] is the concentration of conjugate base and [HA] is the concentration of the weak acid.

In my opinion, the best pair of weak acid and its conjugate will be of phosphoric acid and sodium hydrogen phosphate. There are two reasons behind opting that:

1. It does not contain any oxidising element which can cause a parallel reaction of oxidising iodide.

2. It is the strongest weak acid so it will yeild H+ ions in maximum amount leading to increased rate of reaction.

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