Question

Hydrazine, N2H4(aq), is used in the preparation of polymers, pharmaceuticals and rocket fuel. Hydrazine has alkaline properties similar to ammonia and will act as a weak base. Given that a 100 mL sample of 0.10 mol/L hydrazine solution has a pH of 10.55 at 25.0 oC, write the formula for the conjugate acid and calculate the Kaof the conjugate acid.

I understand that we have to write the equation for the conjugate acid but I don't understand how to find the values then. I'm hoping someone can help me using the ICE (Initial, Change, Equilibrium) table.

Answer 1

Technically it has two ionizations but the second one is so weak we can ignore it.
pH = 10.55 so pOH = 3.45. Convert that to OH^. That is about 3E-4 but that's just an estimate.
..................N2H4 + H2O ==> N2H5^+ + OH^-
I.................0.1...........................0.................0
C.................-x............................x.................x
E...............0.1-x..........................x..................x
and you know OH^- and N2H5^+ from the above.

Write the Kb expression for N2H4 and substitute the E line and solve for Kb N2H4.
Calculate Ka for the conjugate acid from KaKb = Kw = 1E-14. Post your work if you get stuck.

Answer 2

Thank you so much!
I just needed help starting it off and this helped a lot!!

Answer 3

We cant consider the change in the concentration of the N2H4 negligible so do we have to use the quadratic formula to derive Kb?

Answer 4

Given the value of the question I doubt this is the correct way to go about solving this problem..