Problem Solver (Chem 2)

You are given:

HA ⇌ H⁺ + A^-

Initial Concentration - HA = 0.50 M

K_a =1.0 × 10^-5

You are expected to FIND THE PH.

How do you solve this?

1. Make an ICE table (putting known initials in their place. Filling out C based on if reactant or product coefficient [left is negative right is positive]. E is just I - C.)

2. Plug into K_a formula: [Products^{(coefficients)}]/[Reactants^{(coefficients)}]

3. Determine if weak acid or not (less than 1) - If so, only a tiny amount breaks.

4. Solve for x.

5. X is [H⁺], so solve for pH ( - log [H⁺}

You are given:

HA ⇌ H⁺ + A^-

Initial Concentration - HA = 0.50 M

K_a =1.0 × 10^-5

You are expected to find the Percent Ionization.

How do you solve this?

1. Make an ICE table (putting known initials in their place. Filling out C based on if reactant or product coefficient [left is negative right is positive]. E is just I - C.)

2. Plug into K_a formula: [Products^{(coefficients)}]/[Reactants^{(coefficients)}]

3. Determine if weak acid or not (less than 1) - If so, only a tiny amount breaks.

4. Solve for x.

5. X is [H⁺], so solve for pH ( - log [H⁺}

6. Plug everything into the % formula = (H⁺/initial) * 100 [H⁺ is just x]

You are given K_a = 6.6 × 10^-4 for the weak acid HF. Find K_b.

Formula: K_a * K_b = K_w

1. Recall that K_w = 1.0 × 10^-14

2. Plug in K_a and K_w and solve.

A solution has a pH of 3.45. What is the concentration of H⁺ in the solution?

1. Recall that → pH = - log [H⁺]

2. Rearrange what you need to find [H⁺] to the left side. [H⁺] = 10^(-pH)

3. Plug in and solve.

You are given: Weak acid [HA]

K_a = 1.8 × 10^-5

[HA] = 0.20 M

[A^-] = 0.15 M

Find the pH.

1, Recognize it is a buffer: [HA] and [A^-]

2. Do to it being a buffer, use the Henderson formula: pH = pK_a + log (base/acid)

3. Solve for pK_a → pK_a = - log (K_a)

4. Plug into the Henderson formula

Given Ca²⁺ ⇌ Ca²⁺ + 2F^-

K_sp = 3.9 × 10^-11

Find solubility (x) of CaF_2.

1. Make an ICE table (putting known initials in their place. Filling out C based on if reactant or product coefficient [left is negative right is positive]. E is just I - C.)

2. Plug into K_a formula: [Products^{(coefficients)}]

3. Solve for x.