True or False a. ____ The equilibrium constant for 2H+ + 2OH- 2H2O is equal to K

Question

True or False

a. ____ The equilibrium constant for 2H+ + 2OH- 2H2O is equal to K = 1028.

b. ____ If the Ka for HA is 2.0 x 10-9, the base ionization constant (Kb) for it’s A- is 5.0 x 10-6.

c. ____ The titration of 100 mL of 0.20M weak base with 50 mL of 0.20M HCl will result in a solution with a pH equal to the pKa of the conjugate acid.

d. ____ The acid-base conjugate pair from part b could be used to create a buffered solution.

e. ____ Buffer capacity increases as the [A-]/[HA] ratio approaches from 1.0.

f. ____ In pure water at 60oC [H+] = [OH-] = 3.1 x 10-7 thus a solution at 60o C with a pH of 6.5 will be basic.

g. ____ A solution containing an acid-base indicator with a Ka = 10-8 in which its undissociated form (HA) is yellow and its dissociated form (A-) is blue would be expected to be green at a pH of 8.

h) ____ The percent dissociation of water into H+ and OH- would be expected to be greater in salt water than in pure water.

i) ____ The Ka of hydronium ion is given by [H2O].

j) ___ For an ideal solution all activity coefficients are equal to 1.0

k) ___ For a non-ionic solute in a solution that “salts out” with increasing ionic strength its activity coefficient must decrease with increasing ionic strength.

l) ___ The pKa of water acting as an acid is 15.74.

m) ___ Any molecule with an acid dissociation constant (Ka) greater than 56 is a strong acid (stronger than hydronium ion).

n) ___ In the reaction, BF3 + NH3 F3B-NH3 ammonia is acting as a Lewis base only.

o) ___ An aqueous solution of Cu(NO3)2 would be colorless (draw the electron configuration to make sure).

Explanation / Answer

a.False (equlibrium constant of water Kw = 1 X 10-14)

b.True (Ka X Kb value should be 1 X 10-14

           Here Ka.Kb = 2.0 X 10-9 X 5.0 X 10-15 = 10-14)

c.False

d.True

e.True

f. False (here concentrations of H+ and OH- ions are same, so it is neutral)

g.True

h.True

i. False (pure H2O cannot give H+ ions)

j.True

k.True

l. False

m.True

n. True (in this NH3 is donating electrons to BH3 molecule, so, NH3 is lewis base)

o. False (Cu+2 shows blue colour in aqeous medium)

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