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Jobisdone [24]
3 years ago
13

Consider a 125 mL buffer solution at 25°C that contains 0.500 mol of hypochlorous acid (HOCl) and 0.500 mol of sodium hypochlori

te (NaOCl). What will be the pH of this buffer solution after adding 0.341 mol of HCl? The Ka of hypochlorous acid is 2.9 x 10-8 . Assume the change in volume of the buffer solution is negligible
Chemistry
1 answer:
Helga [31]3 years ago
6 0

Answer:

pH = 6.82

Explanation:

To solve this problem we can use the<em> Henderson-Hasselbach equation</em>:

  • pH = pKa + log\frac{[NaOCl]}{[HOCl]}

We're given all the required data to <u>calculate the original pH of the buffer before 0.341 mol of HCl are added</u>:

  • pKa = -log(Ka) = -log(2.9x10⁻⁸) = 7.54
  • [HOCl] = [NaOCl] = 0.500 mol / 0.125 L = 4 M
  • pH = 7.54 + log \frac{4}{4}
  • pH = 7.54

By adding HCl, w<em>e simultaneously </em><u><em>increase the number of HOCl</em></u><em> and </em><u><em>decrease NaOCl</em></u>:

  • pH = 7.54 + log\frac{[NaOCl-HCl]}{[HOCl+HCl]}
  • pH = 7.54 + log \frac{(0.500mol-0.341mol)/0.125L}{(0.500mol+0.341mol)/0.125L}
  • pH = 6.82
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Answer:

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When percentage composition is given, and asked for the empirical formula, it is simplest to  assume 100 g of material. Thus,

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Mass H = 4.58 g.  Moles H = 4.58 g x 1 mole/1.0 g = 4.58 moles H

Mass O = 54.50 g.  Moles O = 54.50 g x 1 mole/16 g = 3.41 moles O

Now, we want to get the moles into whole numbers, so we begin by dividing all by the smallest, i.e. divide all values by 3.41.

Moles C = 3.41/3.41 = 1

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Now, in order to get 1.34 to be a whole number we multiply it (and all others) by 3

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