Question

What is the correct relationship between the pHs of isomolar solutions of sodium oxide (pH1),sodium sulphide (pH2),sodium selenide (pH3) and sodium telluride (pH4)?

• A. pH1 > pH2 $\approx$ pH3 > pH4
• B. pH1 < pH2 < pH3 < pH4
• C. pH1 < pH2 < pH3 $\approx$ pH4
• D. pH1 .> pH2 > pH3 > pH4

Answer 1

Answer: (D)

pH1 .> pH2 > pH3 > pH4

Answer 2

Each of the aforementioned compounds transforms into its corresponding base when dissolved in water.
When these oxides are dissolved in water, the basicity of the solution similarly reduces as the basicity of the oxides does.
NaOH+H2O = Na2 O+2H2O
NaOH+H2S+2H2 O+Na2S
NaOH+H2 Se+Na2 Se+2H2O
NaOH+H2 Te+Na2 Te+2H2O
H2 Te is neutralised by NaOH before H2 Se, H2S, and H2O.

Therefore, the correcr option is (D): pH1 .> pH2 > pH3 > pH4