Question

For the reaction of hydrazine (N₂H₂) in water, H₂NNH₂(aq) + ₂O(l) <=> H₂NNH₃⁺ (aq)+ OH⁻(aq) Kb is 3.0x10⁻⁶(aq). Calculate the concentrations of all species and the pH of a 2.0 M solution of hydrazine in water.

Answer 1

First, set up an equation using the reaction and the equilibrium constant Kb. Assume a small reaction fraction x and calculate the equilibrium concentrations of all the species. Calculate the pH from the hydroxide ion concentration.

Step-by-step explanation:

To calculate the concentrations of all species in the solution, we first need to set up an equilibrium expression based on the reaction:

H₂NNH₂(aq) + ₂O(l) <=> H₂NNH₃⁺ (aq)+ OH⁻(aq)

from which we have

[H₂NNH₃⁺][OH⁻] / [H₂NNH₂] = Kb = 3.0 x 10⁻⁶.

Assuming a small fraction x of the 2.0 M hydrazine reacts, the concentrations at equilibrium are then

[H₂NNH₂] = 2.0 - x, [H₂NNH₃⁺] = x, and [OH⁻] = x.

Substituting these into the equilibrium expression and solving for x (using the assumption that x << 2.0 to simplify the calculation), we can find the OH⁻ concentration.

The pH can then be calculated as 14 - pOH, where the pOH is the negative log of the OH⁻ concentration.

Learn more about Acid-Base Equilibrium