Chemistry 212R Unit 3

Acids/Bases

100

True or false? All Arrhenius acids increase the [H₃O⁺] when dissolved in water.

True.

200

True or false? All Bronsted-Lowry bases can also be categorized as Arrhenius bases.

False -- the other way around.

300

What must Lewis acids contain structurally?

A vacant orbital to accept an electron pair.

(These are usually cations like Ca²⁺, Fe³⁺, etc.)

400

What type(s) of acid or base is NaOH?

Arrhenius base - contains OH in its formula

Bronsted-Lowry base - it is first Arrhenius

500

True or false? The stronger a weak base is, the weaker its conjugate acid is. Explain your reasoning.

True. (decide if reasoning complies)

Conversions

100

What is the pH of a solution with [H₃O⁺] = 5.8x10^-6M?

5.24 (acidic solution)

200

What is the [OH^-] of a solution with a pH of 9.4?

2.51x10^-5M

300

What is the K_b of a solution with a pK_a of 5.9?

7.94x10^-9

400

A weak acid solution has a concentration of 0.36M, and it has a K_a = 2.63x10^-6. What is the pH of the solution in water?

3.01

500

A weak base solution has a concentration of 0.74M, and it has a K_a = 3.24x10^-12. What is the pH of the solution in water?

12.68

Salts

100

Is KNO₃ overall acidic, neutral, or basic?

Neutral

200

Is NH₄Br overall acidic, basic, or neutral?

Acidic

300

Is NaF overall acidic, neutral, or basic?

Basic

400

True or false? Salts derived from strong acids and strong bases have a substantial effect on pH.

False – this is why they are neutral. They have no effect on pH at all.

500

True or false? Acids derived from strong acids and strong bases will have a pH close to 7.

True – they essentially neutralize each other.

Titrations

100

True or false? The pH of a weak acid-strong base titration at the equivalence point is 7.

False. This is true for strong acid-strong base titrations.

200

True or false? The pH of a strong acid-strong base titration should be below 7 at the equivalence point.

False.

300

How do you calculate the pH of a weak acid-strong base titration before any base is added?

You make an ICE table with the weak acid + water, which produces H₃O⁺ + conjugate base. Take the negative log of the equilibrium concentration of H₃O⁺.

400

How do you calculate the pH of a weak acid-strong base titration at the equivalence point?

Set it up like a weak base equilibrium! React the conjugate base (weak base) with water to product the weak acid and OH^-. Use [OH^-] to calculate pOH, then to pH from there.

500

In a weak acid-strong base titration, there are 0.004mol excess base in a 120mL solution. What is the pH of the solution after this titration?

pH = 12.52