Question

Determine the pH during the titration of 14.7 mL of 0.118 M hydroiodic acid by 8.94×10-2 M sodium hydroxide at the follo...

Determine the pH during the titration of 14.7 mL of 0.118 M hydroiodic acid by 8.94×10-2 M sodium hydroxide at the following points:

(1) Before the addition of any sodium hydroxide

(2) After the addition of 9.70 mL of sodium hydroxide

(3) At the equivalence point

(4) After adding 24.6 mL of sodium hydroxide

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Answer #1

1)when 0.0 mL of NaOH is added

Given:

M(HI) = 0.118 M

V(HI) = 14.7 mL

M(NaOH) = 0.0894 M

V(NaOH) = 0 mL

mol(HI) = M(HI) * V(HI)

mol(HI) = 0.118 M * 14.7 mL = 1.7346 mmol

mol(NaOH) = M(NaOH) * V(NaOH)

mol(NaOH) = 0.0894 M * 0 mL = 0 mmol

We have:

mol(HI) = 1.735 mmol

mol(NaOH) = 0 mmol

0 mmol of both will react

remaining mol of HI = 1.735 mmol

Total volume = 14.7 mL

[H+]= mol of acid remaining / volume

[H+] = 1.735 mmol/14.7 mL

= 0.118 M

use:

pH = -log [H+]

= -log (0.118)

= 0.9281

Answer: 0.928

2)when 9.7 mL of NaOH is added

Given:

M(HI) = 0.118 M

V(HI) = 14.7 mL

M(NaOH) = 0.0894 M

V(NaOH) = 9.7 mL

mol(HI) = M(HI) * V(HI)

mol(HI) = 0.118 M * 14.7 mL = 1.7346 mmol

mol(NaOH) = M(NaOH) * V(NaOH)

mol(NaOH) = 0.0894 M * 9.7 mL = 0.8672 mmol

We have:

mol(HI) = 1.735 mmol

mol(NaOH) = 0.8672 mmol

0.8672 mmol of both will react

remaining mol of HI = 0.8674 mmol

Total volume = 24.4 mL

[H+]= mol of acid remaining / volume

[H+] = 0.8674 mmol/24.4 mL

= 3.555*10^-2 M

use:

pH = -log [H+]

= -log (3.555*10^-2)

= 1.4492

Answer: 1.45

3)

So, pH at equivalence point will be neutral which is 7.00

Answer: 7.00

4)when 24.6 mL of NaOH is added

Given:

M(HI) = 0.118 M

V(HI) = 14.7 mL

M(NaOH) = 0.0894 M

V(NaOH) = 24.6 mL

mol(HI) = M(HI) * V(HI)

mol(HI) = 0.118 M * 14.7 mL = 1.7346 mmol

mol(NaOH) = M(NaOH) * V(NaOH)

mol(NaOH) = 0.0894 M * 24.6 mL = 2.1992 mmol

We have:

mol(HI) = 1.735 mmol

mol(NaOH) = 2.199 mmol

1.735 mmol of both will react

remaining mol of NaOH = 0.4646 mmol

Total volume = 39.3 mL

[OH-]= mol of base remaining / volume

[OH-] = 0.4646 mmol/39.3 mL

= 1.182*10^-2 M

use:

pOH = -log [OH-]

= -log (1.182*10^-2)

= 1.9273

use:

PH = 14 - pOH

= 14 - 1.9273

= 12.0727

Answer: 12.07

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