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6. Titration curves. A jump of titration and its importance for selecting
an indicator.
Input test-control on the topics «Concentration of solutions and acid-base
titration».
Homework exercises.
1. 10.8 ml of a 0.108 M solution of NaOH was used for titrating 10 ml of
gastric juice. Calculate the normality of hydrochloric acid in gastric juice and its
pHvalue.
Answer
: 0.117 mol/l; 0.93.
2. Titration of 5 ml of sodium hydroxide solution consumed 4.76 ml of
0.106 M hydrochloric acid. Calculate the normality and titer of the sodium
hydroxide solution.
Answer
: 0.101 mol/l; 0.00404 g/ml.
3. TheKOHsamplewith amass of 1.2046g is dissolved in a 250ml volumetric
flask. For titration of 20 ml of the resulting solution was used 14.82 ml of a
0.105M hydrochloric acid solution. Determine the content (in%) of KOH in the
sample. Answer: 90.5%.
4. Titration of 45 ml of phosphoric acid required 28.3 ml of a 0.1 M solution
of KOH. Write the equation of the reaction, calculate the pH value of the
phosphoric acid’s solution, if degree of dissociation (α) is 0.035.
Answer
: 2.65.
5. A 10% solution of ammonium hydroxide, called ammonia, is used in
medicine to excite the respiratory center. Titration of 10 ml of ammonia
consumed 27.4 ml of 1 mol/l hydrochloric acid. Determine the pH value of 10%
ammonia solution. (
K
b
(NH
4
OH) = 1.75×10
–5
).
Answer
: 11.84.
Laboratory work:
Determination of the titer and molar concentration of the
equivalent solution of soda by neutralization.
Way of work: the exact concentration of (Na
2
CO
3
) soda in the solution is
determined by the titrimetric method. The titrant is a solution of nitric acid. For
10 ml of the analyzed solution, the measuring cylinder is transferred to four
flasks for titration. Each solution is titrated from the burette with a solution of
nitric acid in the presence of methylorange. Example of calculation:
Test titration
V tr. = 13.0 ml
Precise titration
V
1
= 12.2 ml
V
2
= 12.1 ml
Titration is considered accurate if the difference between the volumes is not
more than 0.2 ml.
1 2
av.
3
(HNO )
2
V V
V
+
=