Unit 8.3 - Weak Acid and Base Equilibria

What defines a Brønsted-Lowry acid?

A substance that donates a hydrogen ion (proton donor).

In the dissociation of an acid HA, what is the conjugate base?

A minus (A¬−), which is what HA becomes after donating a hydrogen ion.

What is the equilibrium constant for weak acids referred to as?

K_a, which stands for acid dissociation constant.

How do we represent a strong acid's K_a value?

Essentially infinity, because a strong acid dissociates nearly completely.

What happens to percent dissociation as an acid becomes more dilute?

Percent dissociation increases.

What do you do when calculating the pH of a weak acid?

You start by writing the major species and set up an ICE table.

If an acid is not one of the six strong acids, what can we conclude about it?

It is a weak acid.

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

A strong acid has a weak conjugate base, while a weak acid has a strong conjugate base.

What indicates a weak base in regards to K_b?

K_b values are used for weak bases; strong bases do not have K_b values.

In mixed acid solutions, what do we focus on when calculating pH?

We focus on the acid with the larger K_a value.

What is a polyprotic acid?

An acid that can donate more than one hydrogen, such as carbonic acid.

What can be ignored when calculating pH for polyprotic acids?

The second and subsequent dissociations, since they are mathematically insignificant compared to the first dissociation.

What is the formula for calculating percent dissociation?

Percent dissociation = (amount dissociated / initial concentration) × 100.

During dissociation, what does weak bases produce in terms of ions?

Typically hydroxide ions (OH−).

What happens to the ionization of a weak base like ammonia when it accepts a hydrogen ion?

Very little of the ammonia dissociates into ammonium and hydroxide.

When calculating the pH of a weak base solution, what is preferable to find first?

It's preferable to find the pOH first before calculating pH.

Why is ice table setup important in acid-base problems?

It helps organize calculations and find concentrations at equilibrium.

What is a unique feature of strong acids in relation to K_a?

Strong acids do not have K_a values because they dissociate completely.

In a multiple-choice question regarding weak acids, what simplification can you make?

You can ignore the -x in the equilibrium expression assuming it's negligible.

If a weak acid has a low K_a value, what does that imply about its strength?

It implies that the acid is weak and does not dissociate significantly.

How do you convert pK_a to K_a?

K_a = 10^(-pK_a).