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# Calculating the pH in a flask at points in the titration.

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100.0 ml of 0.100 M acetic acid is placed in a flask and is titrated with 0.100 M sodium hydroxide .

An appropriate indicator is used.

Ka for acetic acid is 1.7 x 10 -5

a. when no NaOH has been added.
b. after 25.0 ml of NaOH is added
c. after 50.0 ml of NaOH is added
d. after 75.0 ml of NaOH is added
e. after 100.0 ml of NaOH is added
f. what would be the appropriate indicator that was used ? consult fig 16.7 in BLB and explain your choice.

g. What would the pH be after 300 ml of 0.100 M NaOH was added.

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Calculate the pH in a flask at points in the titration.
100.0 ml of 0.100 M acetic acid is placed in a flask and is titrated with 0.100 M sodium hydroxide. An appropriate indicator is used. Ka for acetic acid is 1.7 x 10 -5.

a. when no NaOH has been added.

CH3COOH ↔ CH3COO- + H+
Initial concentration 0.1 ----------- -----
Change -x +x +x
Equilibrium concentration 0.1 - x x x

Ka = [CH_3COO^-] [H^+] / [CH_3COOH]
1.7 x 10^-5 = (x)(x) / (0.1 - x)
Assume x as negligible:
1.7 x 10^-5 = x^2 / 0.1
x = 1.304 x 10^-3 = [H^+]

pH = - log [H^+]
pH = - log 1.304 x 10^-3
pH = 2.885

b. after 25.0 ml of NaOH is added

CH_3COOH + OH^- ↔ CH_3COO^- + H_2 ...

#### Solution Summary

This solution explains how to calculate the pH level in a flask for the given chemistry problems.

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