Calculate The Ph of The Following Solutions 0.100 M Honh2

Calculating the pH of a solution containing HONH2 (hydroxylamine) requires understanding the dissociation of this weak base. This guide provides the formula, step-by-step calculation, and interpretation of results for 0.100 M HONH2 solutions.

How to Calculate the pH of HONH2 Solutions

The pH of a solution containing HONH2 can be calculated using the Henderson-Hasselbalch equation, which relates the pH to the concentration of the conjugate acid and base. For HONH2, the relevant equilibrium is:

HONH2 + H2O ⇌ HONH3+ + OH−

The dissociation constant (Kb) for HONH2 is approximately 1.0 × 10−4 at 25°C. The pH calculation involves these steps:

Determine the concentration of OH− ions using the dissociation constant
Calculate the pOH from the OH− concentration
Convert pOH to pH using the relationship pH + pOH = 14

The pH Calculation Formula

The complete formula for calculating the pH of a 0.100 M HONH2 solution is:

pH = 14 - pOH

where pOH = -log[OH−]

[OH−] = √(Kb × [HONH2])

For HONH2, Kb = 1.0 × 10−4 and [HONH2] = 0.100 M.

Worked Example

Let's calculate the pH of a 0.100 M HONH2 solution:

Calculate [OH−]: √(1.0 × 10−4 × 0.100) = √(1.0 × 10−5) = 1.0 × 10−2.5 M
Calculate pOH: -log(1.0 × 10−2.5) = 2.5
Calculate pH: 14 - 2.5 = 11.5

The calculated pH of a 0.100 M HONH2 solution is 11.5.

Interpreting the Results

A pH of 11.5 indicates a strongly basic solution. This is expected for HONH2, which is a weak base. The result shows that the solution contains significant hydroxide ions due to the dissociation of HONH2.

Note: The actual pH may vary slightly depending on temperature and the purity of the HONH2 sample. Always verify with experimental data when possible.

Frequently Asked Questions

What is the dissociation constant for HONH2?: The dissociation constant (Kb) for HONH2 is approximately 1.0 × 10−4 at 25°C.
How does concentration affect the pH of HONH2 solutions?: Increasing the concentration of HONH2 increases the concentration of OH− ions, which lowers the pOH and raises the pH.
Can this formula be used for other weak bases?: Yes, the same approach can be used for other weak bases by substituting the appropriate Kb value.
What factors can affect the accuracy of this calculation?: Temperature changes, impurities in the HONH2 sample, and the presence of other ions can all affect the calculated pH.
How do I verify the calculated pH experimentally?: Use a pH meter or pH indicator strips to measure the actual pH of your solution and compare it to the calculated value.