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Grade: 12

                        

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 dm 3 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

11 years ago

Answers : (1)

askiitian.expert- chandra sekhar
10 Points
							

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

    pH=log 5*10-9

        =9-0.698

        =8.302

2) as the acid is added the pH decreases the only option is 3.8

   therefore ans is 3.8

11 years ago
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