1. For each run of the iodine clock reaction, 5.00 mL of a 3.91×10-2 M arsenious

Question

1. For each run of the iodine clock reaction, 5.00 mL of a 3.91×10-2 M arsenious acid solution is added to the reaction mixture. The total volume of the reaction mixture is 100.0 mL. What is the initial rate of the reaction if the solution turns blue after 21 seconds?

2. A buffer solution was prepared by adding 25 mL of a 0.54 M acetic acid solution and 20 mL of a 0.92 M sodium acetate solution to a 500 mL volumetric flask and diluting to the mark with distilled water. A reaction mixture was buffered with this solution by adding 70 mL. The total volume of the reaction mixture is 100 mL and the ionic strength is 0.29. What is the hydrogen ion concentration of this solution?

Explanation / Answer

(1) From the given data –

Initial rate of reaction = Concentration / Time

                                  = [(3.91x10^-2)/21]*[5/100] = 9.30 x 10^-5 M/s

(2) In case of a buffer solution,

pH = pKa + log(base/acid)

      = 4.75 + log(0.92 x 20/0.54 x 25)

      = 4.88

pH = -log[H+] = 4.88

[H+] = 1.32 x 10^-5 M

Therefore, total [H+] concentration = 1.32 x 10^-5 x 0.29 = 3.8 x 10^-6 M

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