The answers are already provided, I just need really detailed explanations ! Tha

Question

The answers are already provided, I just need really detailed explanations ! Thank you ! ( On number 20 I dont know where 10^-14 comes from!)

20) Phosphorous acid H3PO3 is a diprotic acid with Ka1 = 1.0 x 10-2 and Ka2 = 2.6 x 10-7. What is the Kb of H2PO3- and is a
solution of NaH2PO3 acidic or basic? a) 3.8 x 10-8, acidic
b) 3.8 x 10-8, basic
c) 1.0 x 10-12, basic
d) 1.0 x 10-12, acidic

C is Correct

21) Arsenic acid H3AsO4 is a triprotic acid with Ka1 = 5.6 x 10-3, Ka2 = 1.7 x 10-7, Ka3 = 4.0 x 10-12. What is true for the pHs of solutions of H2AsO4- and HAsO42- in water? a) H2AsO4- > 7, and HAsO42- > 7
b) H2AsO4- < 7, and HAsO42- < 7
c) H2AsO4- > 7, and HAsO42- < 7
d) H2AsO4- < 7, and HAsO42- > 7
e) H2AsO4- = 7, and HAsO42- < 7

C is correct

22) The diprotic acid tartaric acid C4H6O6 has Ka1 = 1.0 x 10-3 and Ka2 = 4.6 x 10-5. What is the Kb of C4H5O6- and is it an acidic or basic solution?
a) 1.0 x 10-11, acidic
b) 1.0 x 10-11, basic
c) 2.2 x 10-10, acidic
d) 2.2 x 10-10, basic
e) 2.2 x 10-10, neutral

(A is correct)

27) We have generally stayed away from small highly charged ions such as the Cu2+ ion since they behave a little differently than other acids and bases. For example in a solution of ammonia, the following reaction will take place between Cu2+ and NH3. Cu2+(aq) + 4NH3(aq)?[Cu(NH3)4]2+ In this situation what would we describe the copper ion as doing? a) Proton donor
b) Proton acceptor
c) Electron pair donor
d) Electron pair acceptor

D is Correct

• Be able to recognize what combination of components makes a buffer. 28) Which of the following solutions will be a buffer?
I. 0.1M NaOH and 0.1M HBr
II. 0.2M HCl and 0.4M NaF
III. 0.1M NH3 and 0.2M NH4Cl
a) i
b) ii
c) iii
d) i and ii
e) ii and iii
29) Which of the following will not make a good buffer (the first substance in each pair is an acid and the second a base)?
a) 0.5M HNO2 and 0.5M NaNO2
b) 0.15M HCl and 0.3M NH3
c) 0.1M HOI and 0.1M NaOI
d) 1.1 M C5H5NHCl and 1.0M C5H5N
e) 0.8M HN3 and 0.8 M NH3

Explanation / Answer

20) H3PO4 dissociatea as,

H3PO4 = H+(aq) + H2PO4-(aq) , Ka1 = 1.0 x 10-2 (first ionisation of H3PO4)

we know that, Ka x Kb = 1.0 x 10-14

or, Kb = (1.0 x 10-14) / (1.0 x 10-2  ) = 1.0 x 10-12  

The solution of NaH2PO3 basic

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