1) Briefly explain why the pH of 1.0*10^-2 MHCl is different from that of 1.0*10

Question

1) Briefly explain why the pH of 1.0*10^-2 MHCl is different from that of 1.0*10^-2M HC2H3O2? 2) Briefly explain why the pH change that resulted when you added 6M NaOH to the buffer solution was of a different magnitude than the pH change that resulted when you added aqueous NaoH to distilled water. 3) Write the chemical equation for the reaction that occurred when you added 6M NaOH to the buffer solution 4)Write the chemical equation for the reaction that occurred when you added 6M HCl to the buffer solution.

Explanation / Answer

1)

concentration of HCl = 1.0 x 10^-2 M .

here HCl is strong acid . it will completely dissociates and give H+ ions. so we take HCl concentration as [H+] concentration directly. so

[H+] = 1.0 x 10^-2

pH = -log [H+] = -log (1.0 x 10^-2 ) = 2

pH = 2.

concentration of HC2H3O2 = 1.0 x 10^-2 M

here it is weak acid . so it will not completely dissociates. so we cant take the concentration of H+ directly as HCl .

so here we consider Ka value of that.

Ka = 1.8 x 10^-5

[H+] = sqrt (Ka x C ) = sqrt (1.8 x 10^-5 x 0.01)

       = 4.24 x 10^-4 M

pH = 3.37.

so the pH is not equal.

3)

buffer is = HC2H3O2 + C2H3O2-

HC2H3O2 ----------------> C2H3O2-

on addition of NaOH this will react with acid which is present in buffer.

HC2H3O2 + NaOH   -------------------> NaC2H3O2 + H2O

4)

on addition of HCl this will react with conjugate base which is present in buffer.

C2H3O2- + HCl   ----------------> HC2H3O2 + Cl-

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