In 25 ml of water sample, few drops of phenolphthalein indicator
solution were added. The colour of solution turned pink. This solution was
titrated with HCl solution and end point of the titration observed at 40.0 ml
[P = 40.0 ml]. In the same solution, when few drops of methyl red indicator
solution were added, its colour changed to pale yellow. This solution was
titrated with HCl solution and end point of the titration observed at 50.0 ml
[M = 50.0 ml].Which type of alkalinity is present in the water sample?
Answers
Answer:
Two drops of phenolphthalein solution was added to 40.0mL of an HCl solution. This solution was titrated with 0.10M NaOH solution. When 30.0mL of base had been added, part of the solution turned pink; but the colour disappeared upon mixing the solution. Addition of NaOH solution was continued dropwise until one drop addition produced a lasting pink colour. At this point, the volume of base added was 32.56mL. Calculate:
(i) The concentration of HCl solutions
(ii) Concentration of HCl in solution when 30.0mL base had been added.
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ANSWER
40 ml of HCl needed 32.56 ml of NaOH 0.10 M
M
1
V
1
=M
2
V
2
40×M
1
=0.1×32.56
M
1
=0.1×
40
32.56
=0.0814
conc. of HCl when 30ml base added :
V
1
+V
2
M
1
V
1
−M
2
V
2
⇒
70
0.0814×40−30×0.1
⇒
70
2.56×0.1
≈0.0037M