A. Calculate the pH of a 0.10 M solution of barium hydroxide, Ba(OH)2

barium-hydroxide

#1

A. Calculate the pH of a 0.10 M solution of barium hydroxide, Ba(OH)2.
B. Calculate the pH of a 0.10 M solution of NaOH.
C. Calculate the pH of a 0.10 M solution of hydrazine, N2H4. Kb for hydrazine is 1.3

Concepts and reason
For strong bases, the pOH of the solution can be calculated directly from the concentration of the solution using the following formula:
image
The relationship between pH and pOH is image.

Fundamentals
For strong bases or acids, 100% ionization takes place. Hence, from the concentration of the base, the concentration of hydroxyl ion can be calculated.
For weak bases or acids, 100 % ionization does not take place. Hence, for weak acids or bases, the concentration of hydroxyl ion can be calculated using the equilibrium expression.

Answer:

Part A
The reaction is as follows:
image
Therefore, the pH of a 0.10 M barium hydroxide solution is 13.3.

Part B
The reaction is as follows:
image
One mole of NaOH gives one moles of image ions.
It is given that the concentration of NaOH solution is 0.10 M.
Hence, the concentration of image ions is 0.010 M.
image
Therefore, the pH of a 0.10 M sodium hydroxide solution is 13.
As sodium hydroxide is a strong base, 100% ionization takes place. The concentration of NaOH solution is equal to the concentration of image ions.

Part C
The reaction is as follows:
image
Now, calculate the concentration of image from the equilibrium expression as follows:
image
Therefore, the pH of a 0.10 M hydrazine solution is 10.56.

Hydrazine is a weak base. Very small fraction of the molecules dissociates into ions. Hence, for weak bases, the concentration of the solution is not equal to the concentration of hydroxyl ion.