15.5 Weak Acids And Acid Ionization Constants

Question 1

What does the ionization constant tell us about the strength of an acid?

Answer 1

Strength of the acid HA is measured quantitatively by magnitude of Ka, that is acid ionization constant

The larger the Ka value, the stronger the acid, the greater the [H+] at equilibrium

Question 2

List the factors on which the Ka of a weak acid depends

Answer 2

1. Ionization constant Ka depend upon the acid strength. Ka values increase with acid strength
2. Ka values also depend on temperature

Question 3

Why do we normally not quote Ka values for strong acids such as HCl and HNo3? Why is it necessary to specify temperature when giving Ka values?

Answer 3

Ka values of strong acids are not given because they are completely ionized in water an does not contain any non-ionized acid molecules hence Ka can not be determined

HCl(aq)->H+(aq)+Cl-(aq)

HNO3(aq)->H+(aq)+NO3-(aq)

It’s necessary to specify temperature when giving Ka values since Ka depend upon temperature. As the temperature change, degree of ionization changes, which alters the Ka value