# Equilibrium Constant

Now that we understand what an acid is, we need a method of quantifying which acids are stronger and which are weaker. ** pH doesn’t work for this**, let me explain why:

## Why we use pKa instead of pH.

The Ka (dissociation constant) describes the ** tendency of a molecule to break apart**. In the case of acids, that specifically means

__donating protons__, which is exactly what we are interested in knowing!

## The relationship between equilibrium constant and pKa.

## The pH scale vs. the pKa scale.

The pH and pKa scales really are completely different. Pardon my French! pKas are obviously something I’m really passionate about.

This is the easiest kind of question you could get. Calculating pKa’s just takes some very simple math.

What is the pKa of acetic acid? Hint:take the negative log of the dissociation constant.

## Calculate the pKa of acetic acid

What is the pKa of ammonium? Hint:take the negative log of the dissociation constant.

## Calculating pKa and comparing acidity

## Do you want more practice?

- The Ka of phenylacetic acid is 5.2 × 10−5, and the pKa of propionic acid is 4.87. Phenyl acetic acid , Ka=5.2...
- 1. CH3CH2OH+NH3⇌CH3CH2O−++NH4 or CH3OH+NH3⇌CH3O−++NH4 b. Which of the four reactions has the most favorable e...
- b. Determine the exact pKa values, using a calculator. c. Which is the strongest acid?
- a. Given the Ka values, estimate the pKa value of each of the following acids without using a calculator (that...
- An acid has a Ka of 4.53×10−6 in water. What is its Keq for reaction with water in a dilute solution? ([H2O]=5...
- (••) For the following acid–base pairs, (iii) predict the favored side of equilibrium; (iv) calculate ; (...
- Calculate K_eq for these acid–base reactions. (c)
- Given that the indicated pKₐ values correspond to the acid dissociation reactions shown, calculate the ratio o...
- (•) For each of the following acid–base reactions, (i) predict which side of the reaction you expect to be fa...
- For the following acid–base reaction, (b) calculate the equilibrium constant.
- (•) For each of the following acid–base reactions, (ii) calculate K_eq , If a pKₐ is not one of the ten c...
- Estimate the K_eq for the following reactions based on the stability of the anions involved. (c)
- Estimate the K_eq for the following reactions based on the stability of the anions involved. (b)
- Estimate the K_eq for the following reactions based on the stability of the anions involved. (a)
- (••) Using pKₐ values, calculate Kₑq for the following acid–base reaction. ⇌
- Using pKₐ values, calculate the equilibrium constants for the following acid–base reactions. (b)
- Calculate Kₑq for the following acid–base reactions. (b)
- (•) Given the pKb, calculate the pKa of the conjugate acid. c.
- (•) Calculate the equilibrium constant for each of the acid–base reactions shown. b.
- Predict the Kₑq for the following acid–base reaction.
- We usually calculate Kₑq for acid–base reactions using pKₐ values. (a) Derive an equation to calculate Kₑq usi...
- (•) Given the pKb, calculate the pKa of the conjugate acid. b.