calculate the kb of ammonia if the ph of .5M solution is 11.48
To calculate the Kb (base dissociation constant) of ammonia (NH3), you need to know the pKa (acid dissociation constant) of its conjugate acid, ammonium (NH4+).
The pKa and pKb values are related by the equation:
pKa + pKb = 14
Since ammonia is acting as a base, we consider the reaction:
NH3 + H2O ⇌ NH4+ + OH-
The dissociation constant expression for this reaction is:
Kb = [NH4+][OH-] / [NH3]
In this case, we can assume that all NH4+ comes from NH3, so [NH4+] = [NH3].
First, we need to calculate the concentration of OH- ions in the solution.
Since the solution has a pH of 11.48, we can use the formula:
pOH = 14 - pH = 14 - 11.48 = 2.52
Now calculate the concentration of OH- ions using the equation:
OH- = 10^(-pOH)
= 10^(-2.52)
Kb = [NH4+][OH-] / [NH3]
= [NH3] * [OH-] / [NH3]
= [OH-]
Therefore, the Kb value of ammonia (NH3) in a 0.5 M solution with pH 11.48 is approximately 10^(-2.52).
To calculate the Kb (base dissociation constant) of ammonia (NH3), you need the pKb value.
The pKb of a substance is defined as the negative logarithm (base 10) of its Kb value. The formula to find pKb is:
pKb = 14 - pOH
First, we need to find the pOH value from the given pH of the solution, using the formula:
pOH = 14 - pH
In this case, the pH of the solution is 11.48, so we can calculate:
pOH = 14 - 11.48
pOH = 2.52
Next, we'll use the pOH value to find the pKb:
pKb = 14 - pOH
pKb = 14 - 2.52
pKb = 11.48
Now, to find the Kb value, we'll take the antilogarithm (base 10) of the pKb value:
Kb = 10^(-pKb)
Kb = 10^(-11.48)
Using a scientific calculator or an online calculator, we can find the Kb value.
Therefore, the Kb value of ammonia (NH3) in the 0.5M solution with a pH of 11.48 is calculated to be Kb = 3.66 x 10^(-12).
pH = 11.48
pOH = 2.52
pOH = -log(OH^-); therefore, OH^- = 0.003 but that's an estimate. You should do it more accurately.
........NH3 + H2O ==> NH4^+ + OH^-
I......0.5.............0.......0
C.......-x.............x.......x
E......0.5-x...........x.......x
x = 0.003 from above.
Substitute into the Kb expression for NH3 and solve for Kb.