Question

The ionization constant ka for HCN is 6.2 x 10^-10 What is the pH of a 0.10 molar solution of sodium cyanide which contains the cyanide ion?

Answer 1

The pH is 5.1

Step-by-step explanation:

1 mole of HCN dissociates to 1mole of hydrogen ion (H+) and 1 mole of cyanide ion (CN-)

Ionization constant of HCN (Ka) = 6.2×10^-10, Molar concentration of HCN = 0.1M

Concentration of hydrogen ion [H+] = √(Ka × [HCN]) = √(6.2×10^-10 × 0.1) = √(6.2×10^-11) = 7.9×10^-6M

pH = -log[H+] = -log(7.9×10^-6) = -(-5.1) = 5.1

Answer 2

5.10

Step-by-step explanation:

HCN ⇄ H⁺ + CN⁻

`K_(a)` of HCN = 6.2 × 10⁻¹⁰ ;

molar solution of sodium cyanide [HCN] = 0.10M

∴ the pH of 0.10 molar solution of which contains the cyanide ion can be calculated as:

=
`\sqrt{6.2*10^(-10)*0.1}`

= 7.874 × 10⁻⁶

∴pH = -log {7.874 × 10⁻⁶}

= 5.10