Determine the pH of the following, giving your answers to two decimal places. I don't know how to do these problems =(

a. 0.100 M ammonia

b. 0.11 M oxalic acid. Assume that dissociation resulting from Ka2 is negligible relative to that from Ka1

1. Write the equation and prepare an ICE chart.

............NH3 + HOH ==> NH4^+ + OH^-
initial......0.100........0........0
change.......-x..........+x.......+x
final.......0.100-x.......x.........x

Kb = (NH4^+)(OH^-)/(NH3)
Substitute into Kb expression from the ICE chart above.
Kb = 1.8E-5 from tables. It will be in your book or in your notes.
1.8E-5 = (x)(x)/0.1-x
Solve for x = OH^- in this case, convert to pOH, then to pH.

The second one is done the same way but it is an acid and not a base. Oxalic has has two Ka values but the problem tells you to ignore the second one and use only k1.
Post your work if you get stuck.

1. not sure where to find Kb as listed as 1.8E^-5?

so is it 1.8E^-5= (NH4+)(NH3)/0.1-X

(9.25)(4.75)/0.1-X = 439.375-X

and how to I convert this to pOH and then to pH?

No. I gave you the formula for finding Kb. They aren't listed in tables because you can calculate them. Kb = (Kw/Ka) = (1E-14/1.8E-5) = 5.55E-10

To determine the pH of a solution, we need to know the concentration of the hydrogen ions (H+). pH is a measure of the acidity or basicity of a solution, and the concentration of H+ ions determines this.

In the case of ammonia (NH3), it is a weak base that reacts with water to form the hydroxide ion (OH-) and ammonium ion (NH4+). Since we are given the concentration of ammonia, we can use the balanced chemical equation to determine the concentration of NH4+ ions.

The balanced chemical equation for the reaction is:

NH3 + H2O ⇌ NH4+ + OH-

The concentration of NH4+ ions is the same as the concentration of OH- ions because they are produced at a 1:1 ratio. So, to find the concentration of OH- ions, we can use the concentration of ammonia.

Step 1: Write the balanced equation for the reaction of ammonia with water

NH3 + H2O ⇌ NH4+ + OH-

Step 2: Write the equilibrium expression for the reaction

Kw = [NH4+][OH-] / [NH3]

Step 3: Substitute the known values into the equilibrium expression

Kw = [x][x] / [0.100]

Step 4: Solve for x (concentration of OH-)

Since the concentration of OH- ions is the same as NH4+ ions, we can substitute [x] for both [NH4+] and [OH-]

Kw = (x)(x) / [0.100]
1.0 x 10^-14 = x^2 / [0.100]

Step 5: Solve for x

x^2 = 1.0 x 10^-14 * [0.100]
x^2 = 1.0 x 10^-15
x ≈ 1.0 x 10^-8

The concentration of OH- ions is approximately 1.0 x 10^-8 M. And since pH = -log[H+], we can determine the pH using the pOH equation:

pOH = -log[OH-]
pOH ≈ -log(1.0 x 10^-8)
pOH ≈ 8

Since pH + pOH = 14 (at 25°C), we can find the pH:

pH = 14 - 8
pH ≈ 6

Therefore, the pH of the 0.100 M ammonia solution is approximately 6.

For the case of oxalic acid (H2C2O4), it is a weak acid that dissociates into two hydrogen ions (H+) and oxalate ions (C2O42-). Since we are given the concentration of oxalic acid, we can use the balanced chemical equation to determine the concentration of H+ ions.

The balanced chemical equation for the dissociation of oxalic acid is:

H2C2O4 ⇌ 2H+ + C2O42-

However, we are told to assume that dissociation resulting from Ka2 (the second ionization constant) is negligible relative to that from Ka1 (the first ionization constant). This means we only need to consider the first ionization of oxalic acid.

Step 1: Write the balanced equation for the first ionization of oxalic acid

H2C2O4 ⇌ H+ + HC2O4-

Step 2: Write the equilibrium expression for the reaction

Ka1 = [H+][HC2O4-] / [H2C2O4]

Step 3: Substitute the known values into the equilibrium expression

Ka1 = [x][x] / [0.11]

Step 4: Solve for x (concentration of H+)

Since the concentration of H+ ions is the same as [x], we can substitute [x] for both [H+] and [HC2O4-]

Ka1 = (x)(x) / [0.11]
x^2 = Ka1 * [0.11]
x^2 ≈ Ka1 * 0.11

(Note: The value of Ka1 for oxalic acid is not provided in the question. You would need to find this value from a reference source or data table.)

Step 5: Solve for x

Calculation of the actual concentration of H+ ions cannot be completed without the value of Ka1. However, once you have the value of Ka1, you can calculate the concentration of H+ ions and then use the pH equation pH = -log[H+] to find the pH of the oxalic acid solution.

Remember, in general, to determine the pH of a solution, you'll need the dissociation constant (Ka or Kb) and the concentration of the acid or base.