Determine the pH of 0.18M NH4Cl.
See above.
To determine the pH of a solution, you need to consider the chemical properties of the solute. For NH4Cl (ammonium chloride), it is a salt that dissociates in water to form ammonium ion (NH4+) and chloride ion (Cl-).
To find the pH of a solution of NH4Cl, you need to determine the concentration of the H+ ion, as it is a measure of acidity. The NH4+ ion can act as an acid by donating a proton (H+) to water, resulting in the formation of NH3 (ammonia) and H3O+ (hydronium ion).
The dissociation of NH4Cl in water can be represented as follows:
NH4Cl(s) → NH4+(aq) + Cl-(aq)
The NH4+ ion acts as an acid in this reaction:
NH4+(aq) + H2O(l) → NH3(aq) + H3O+(aq)
Since you know the concentration of NH4Cl (0.18 M), you can assume that the concentration of NH4+ is also 0.18 M, assuming complete dissociation.
Now, you need to consider the equilibrium constant for the reaction of NH4+ as an acid in water, which is called the acid dissociation constant for NH4+ (Ka). The Ka expression for this reaction is:
Ka = [NH3][H3O+] / [NH4+]
The value of Ka for NH4+ is 5.6 x 10^-10 at 25°C.
Assuming that the initial concentration of NH4+ is 0.18 M and there is no H3O+ initially, you can treat the equilibrium concentration of NH3 and H3O+ as "x".
Therefore, the expression for Ka becomes:
[0.018+x][x] / [0.18-x]
Since x will be very small compared to 0.18 (due to the weak acidic nature of NH4+), you can neglect its contribution in the denominator.
Therefore, the expression for Ka simplifies to:
Ka ≈ x^2 / 0.18
Given that Ka = 5.6 x 10^-10, you can solve for x:
5.6 x 10^-10 ≈ x^2 / 0.18
Solving this equation, you will find the value of x. Then, you can calculate the concentration of H3O+ as x and, subsequently, the pH using the formula:
pH = -log[H3O+]
By plugging in the value of [H3O+], you can find the pH of the solution.