Answer:
6.24
Explanation:
The following data were obtained from the question:
Concentration of HA, [HA] = 0.280 M,
Concentration of H+, [H+] = 4×10¯⁴ M
Concentration of A-, [A−] = 4×10¯⁴ M
pKa =.?
Next, we shall write the balanced equation for the reaction. This is given below:
HA <===> H+ + A-
Next, we shall determine the equilibrium constant Ka for the reaction. This can be obtained as follow:
Equilibrium constant for a reaction is simply the ratio of concentration of the product raised to their coefficient to the concentration of the reactant raised to their coefficient.
The equilibrium constant for the above equation is given below:
Ka = [H+] [A−] /[HA]
Concentration of HA, [HA] = 0.280 M,
Concentration of H+, [H+] = 4×10¯⁴ M
Concentration of A-, [A−] = 4×10¯⁴ M
Equilibrium constant (Ka) =
Ka = (4×10¯⁴ × 4×10¯⁴) / 0.280
Ka = 1.6×10¯⁷/ 0.280
Ka = 5.71×10¯⁷
Therefore, the equilibrium constant for the reaction is 5.71×10¯⁷
Finally, we shall determine the pka for the reaction as follow:
Equilibrium constant, Ka = 5.71×10¯⁷
pKa =?
pKa = – Log Ka
pKa = – Log 5.71×10¯⁷
pKa = 6.24
Therefore, the pka for the reaction is 6.24.
ad then 
, where 
is the sea level weight, 
the sea level accel., 
the accel. above while 
the weight above.