Answer: the expression for the acid-ionization constant (Ka) is [H+][NO2-] / [HNO2], and the pKa for HNO2 is approximately 3.35.
Step-by-step explanation:
The expression for the acid-ionization constant (Ka) is the ratio of the concentration of the products to the concentration of the reactants in an acid-ionization reaction. For the weak acid nitrous acid (HNO2), the acid-ionization reaction can be represented as follows:
HNO2 ⇌ H+ + NO2-
The acid-ionization constant (Ka) can be expressed as:
Ka = [H+][NO2-] / [HNO2]
Given that the acid-ionization constant for nitrous acid is 4.5×10^-4, we can plug in the known concentrations to calculate the pKa.
pKa is defined as the negative logarithm (base 10) of the acid-ionization constant (Ka). Therefore, the formula for calculating pKa is:
pKa = -log10(Ka)
By substituting the value of Ka (4.5×10^-4) into the equation, we can calculate pKa:
pKa = -log10(4.5×10^-4)
Calculating this expression, we find that the pKa for HNO2 is approximately 3.35.
In summary, the expression for the acid-ionization constant (Ka) is [H+][NO2-] / [HNO2], and the pKa for HNO2 is approximately 3.35.