Equilibrium Question 417

Question: 20ml of 0.5N,HCl and 35,ml of 0.1N,NaOH are mixed. The resulting solution will [KCET 2005]

Options:

A) Be neutral

B) Be basic

C) Turn phenolphthalein solution pink

D) Turn methyl orange red

Show Answer

Answer:

Correct Answer: C

Solution:

(i) 20 ml of 0.5 N HCl 0.5N1000,ml,0.5,mole,HCl is present in 20,ml

=20×0.51000=1.0×102 (ii) 35 ml of 0.1 N NaOH 0.1N1000ml of 0.1 mole NaOH is 35 ml =35×0.11000=0.35×102 Total = 20 + 35 = 55 ml.
(1.0-0.35)10-2=0.65 ´ 10-2mole HCl HCl = H++Cl-
[HCl] = [H+]+[Cl-] 55 ml contains 0.65 ´ 10-2 mole of H+ ions 1000,ml0.65×102×10355=6.555

pH=log[H+]=log(6.5/55)

=log55log6.5=0.92 Due to acidic nature of solutions the colour of phenolphthalein becomes pink.



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