A gas compound, HA, has a density of 1.28 g L-1 at 27 C and 0.982 atm. The aqueous solution of this gas compound is acidic because of the partial ionization of HA. When the 2.48 g of HA is dissolved in water and diluted to exactly 1.0 L, the pH of this solution is measured as 4.98 at 27 C. Calculate the Ka of HA. (R = 0.082 L atm/mol K)