Calculate the ph of a buffer solution that is 0.10M in ammonia and 0.15M in ammonium chloride .kb for ammonia is 1.8*10^-5
Use the Henderson-Hasselbalch equation.
pH = pKa + log [(base)/(acid)]
The base will be NH3. The acid is NH4Cl.
What is the molar mass of a compound if 0.27 mol has a mass of 37.3 g
To calculate the pH of a buffer solution that contains ammonia (NH3) and ammonium chloride (NH4Cl), you need to consider the equilibrium between ammonia and ammonium ion (NH4+). Here's how you can calculate the pH:
1. Write the balanced equation for the reaction between ammonia and water:
NH3 + H2O ⇌ NH4+ + OH-
This reaction occurs due to the autoionization of water.
2. Construct the equilibrium expression for the reaction:
Kb = [NH4+][OH-] / [NH3]
The Kb value for ammonia is given as 1.8*10^-5.
3. Determine the concentrations of ammonia (NH3) and ammonium ion (NH4+) in the buffer solution. In this case, the concentration of ammonia is given as 0.10 M, and the concentration of ammonium chloride is given as 0.15 M.
4. Assume that, at equilibrium, the change in concentration of NH4+ and OH- is equal (due to stoichiometry). Let's represent this change as 'x'.
Therefore, the concentration of NH4+ and OH- at equilibrium is 0.15 + x M, and the concentration of NH3 is 0.10 - x M.
5. Substitute the concentrations into the equilibrium expression:
(0.15 + x)(0.15 + x) / (0.10 - x) = 1.8*10^-5
6. Solve the quadratic equation for 'x'. Multiply both sides by (0.10 - x) to eliminate the denominator:
(0.15 + x)(0.15 + x) = 1.8*10^-5 * (0.10 - x)
0.0225 + 0.15x + 0.15x + x^2 = 1.8*10^-6 - 1.8*10^-5x
7. Simplify and rearrange the equation:
x^2 + 0.3x - 1.8*10^-6 = 0
8. Solve the quadratic equation using the quadratic formula or calculator:
The solutions for 'x' are approximately -0.00288 and -0.11012.
Since 'x' represents the concentration change, it must be positive. Therefore, 'x' is approximately 0.11012 M.
9. Calculate the concentration of OH-:
[OH-] = 0.15 + x = 0.15 + 0.11012 = 0.26012 M
10. Calculate the concentration of H+:
[H+] = Kw / [OH-] = 1.0*10^-14 / 0.26012 = 3.8*10^-14 M
11. Calculate the pH:
pH = -log[H+] = -log(3.8*10^-14) ≈ 13.42
Therefore, the pH of the buffer solution is approximately 13.42.