Ques1) The dissociation const of HCN is 5 x 10 -¹⁰ . The pH of the soln prepared by mixing 1.5 moles of HCN and 0.15 moles of KCN in water and making up the total volume to 0.5 dm³ is
(a) 8.302 (b) 7.303 (c) 10.302 (d)9.302

Ques2) 10 ml of an aqeous soln of some strong acid having pH =2 is mixed with 990 ml of the buffer soln with pH = 4. The pH of the resulting soln is
(a) 4 (b) 4.10 (c) 3.8 (d)4.25

Question

askiitian.expert- chandra sekhar · Answer

Hi Tushar,

1) 1/2 lit solution

[KCN]=0.15*2=0.3

initial concentration of [HCN]=1.5*2=3

therefore

(0.3+x)*x/3=5*10^-10 3-x≈3

0.3+x≈0.3

x=5*10^-9

p^H=log 5*10^-9

=9-0.698

=8.302

2) as the acid is added the p^H decreases the only option is 3.8

therefore ans is 3.8

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