Acid Dissociation and Effusion

Assistance with the following questions

1) If the acid dissociation constant, Ksuba, for an acid HA is 8 x 10^-4 at 25 degree C, what percent of the acid is dissociated in a 0.50 M solution of HA at 25 degree C?

2) Equal numbers of moles of Hsub2(g), Ar(g), and Nsub2(g) are placed in a glass vessel at room temperature. If the vessel has a pin sized leak, which of the following will be true regarding the relative values of the partial pressures of the gases remaining in the vessel after some of the gas mixture has effused?

a) PsubH2 < PsubN2 < PsubAr

b) PsubH2 < PsubAr < PsubN2

c) PsubN2 < PsubAr < PsubH2

d) PsubAr < PsubH2 < PsubN2

e) PsubH2 = PsubAr = PsubN2