What is the pH of a 0.0353M solution of NH4F and a 0.0000666M solution of NH4F?
(H^+) of a salt of weak acid + weak base (NH4F is such a salt) is sqrt(KwKa/Kb)
Does ph differ with changes in concentration?
In theory no. In practice, probably so. Since pH = 7 + 1/2 pKa - 1/2 pKb there is no concn term; therefore, it isn't concn dependent.
To determine the pH of a solution, we need to know the concentration of the hydrogen ions (H+) present in the solution. In this case, NH4F is a salt that dissociates to produce ammonium ions (NH4+) and fluoride ions (F-). The ammonium ion can undergo hydrolysis in water, leading to the formation of hydrogen ions, which affects the pH.
To calculate the pH, we need to consider the hydrolysis reaction of NH4+. The equilibrium expression for the hydrolysis of NH4+ is:
NH4+ (aq) + H2O(l) ⇌ NH3(aq) + H3O+ (aq)
The equilibrium constant expression for this reaction can be represented by:
Ka = [NH3(aq)][H3O+ (aq)]
[NH4+(aq)]
Now, let's solve the problem for both concentrations given:
1. For a 0.0353M solution of NH4F:
a) First, we need to find the concentration of NH4+ ions. Since NH4F is a strong electrolyte, it dissociates completely, producing one NH4+ ion for every NH4F formula unit. Therefore, the concentration of NH4+ ions is also 0.0353M.
b) Using the equilibrium constant expression, we can substitute the concentration of NH4+ ions as the concentration of NH3 and H3O+ ions:
Ka = [NH3(aq)][H3O+ (aq)]
[NH4+(aq)]
Ka = [0.0353][H3O+ (aq)]
[0.0353]
c) The concentration of H3O+ ions will be equal to the concentration of NH3 ions because one H3O+ ion is produced for every NH3 molecule formed. Therefore, we can substitute the concentration of NH3 with x:
Ka = [x][x]
[0.0353]
Since the ratio of the concentrations of NH3 to NH4+ is small, we can assume that x will be negligible compared to 0.0353.
d) Simplifying the equation, we have:
Ka = x^2 / 0.0353
e) Now, we can solve for x by rearranging the equation:
x^2 = Ka * 0.0353
Taking the square root of both sides:
x = √(Ka * 0.0353)
f) We need to know the value of the Ka constant for NH4+. The Ka value for NH4+ can usually be found in a chemistry reference book or online.
2. For a 0.0000666M solution of NH4F:
Follow the same steps as above, but substitute 0.0000666M for the initial concentration of NH4+ ions.
Please note that getting the exact value for the pH may depend on additional factors, such as the temperature and other ionic species present in the solution.