LT#6: Weak Acid/Bases

Question 1

Describe the limitations of the Arrhenius Acid/Base Theory

Answer 1

1. Free H1+’s can’t be found in solution. They immediately react with water and form H3O1+, called a hydronium ion. Arrhenius does not include this interaction.
2. It only explains acids and bases in aqueous solutions. Acids and bases also exist as gases.
3. It does not explain several compounds such as NH3 and amines which are bases.

Question 2

What theory/calculation method do you use with Weak Acids/Bases

Answer 2

Bronsted-Lowry. Write an equilibrium reacting your Acid/Base with water and use and equilibrium calculation with and ICE Table.

Question 3

Define a Bronsted-Lowry Acid

Answer 3

Any chemical that can donate a proton

Question 4

Define a Bronsted-Lowry Base

Answer 4

Any chemical that can accept a proton

Question 5

Define Conjugate Acid

Answer 5

The base after it has accepted a proton.

In the reverse reaction it donates a proton.

Question 6

Define Conjugate Base

Answer 6

The acid after it has lost a proton.

In the reverse reaction it accepts a proton.

Question 7

Brønsted-Lowry Theory describes acid-base reactions as…

Answer 7

Equilibria that involve a proton transfer between chemicals.

Question 8

What is the difference between a Kc and Ka?

Answer 8

Water is ignored in the equilibrium expression because it is a pure liquid and its concentration does not change.

Question 9

What is the relationship between the strength of an acid/base and its conjugates?

Answer 9

Inverse relationship. The stronger the acid/base, the weaker its conjugate base/acid.

Question 10

If you need the Kb of a base and can’t find it, how can you mathematically determine it?

Answer 10

Look up the Ka of the conjugate acid and use Ka x Kb = Kw