In the following reaction identify the acid and its conjugate base and the base

Question

In the following reaction identify the acid and its conjugate base and the base and its conjugate acid. Na2CO3 + 2HC2H3O2 Righrarrow H2CO3 + 2NaC2H3O2 NaHS + NaH2PO4 Rightarrow Na2S + H3PO4 NaHS + NaH2PO4 Rightarrow H2S + Na2HPO4. To standardize a potassium permanganate solution a student takes 0.500g of FeSO4 dissolves it in water and titrates the solution until it reaches and endpoint. What is the concentration if 25.50 ml of the potassium permanganate solution is used? (unbalanced) If the student the uses 15.35ml of the same potassium permanganate solution to then titrate a 1.500g sample that contains iron, what is the percent by mass of the iron?

Explanation / Answer

Q17)

      i) Na2CO3 is changed to H2CO3 so they are not conjugate base- acid pair.

      HC2H3O2 (acid) changes to its conjugate base C2H3O2-

   ii) NaHS (acid) to Na2S of S-2 (conjugate base)

      NaH2PO4 or H2PO4-(base) to H3PO4 (conjugate acid)

   iii) NaHS or HS- (base) to H2S(conjugate acid)

      NaH2PO4 or H2PO4- (acid) to Na2HPO4 or   HPO4-2 (conjugate base )

Q18)

a) equivalents of Fe = equivalents of potassium permanganate

     n- factor of Fe = 1 (since Fe+2 changes to Fe+3) and n- factor of permangante is 5 (Mn+7 to Mn+2)

    0.500/151.9 = 25.5 x molarity x 5 /1000

molarity = 0.0258M

b) again equivalents of iron = equivalents of permanganate

here iron (0) changes to iron (3) hence n- factor is 3 for iron

    let q g be the weight of pure iron.

then q x3/55.85= 15.35 x5 x0.0258 /1000

then wt of pure iron -=0.03686g

% purity of sample = 0.03686 x 100/1.5 =2.45 %

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