Miscellan aneous problems involving Weak Bases and perhaps their Conjugates 45.
ID: 636347 • Letter: M
Question
Miscellan aneous problems involving Weak Bases and perhaps their Conjugates 45. Phosphoric acid is a triprosic acid, iomizing in the flowing sequential steps: 46. Phosphoric acid is a triprotic acid, ionizing in the following sequential stcps Write the K, expression for the base, sodium dihydrogen phosphate (NalH PO.)? 47. Use the following acid ionization constants to identify the correct decreasing order of base strengths. HF K,-7.2 x10 HNO, K, -4.5 x 10 HCN K,-62 x 10 48. Three acids found in foods are lactic acid (in milk products), oxalic acid (in rhubarb), and malic acid (in apples). The pK, values are LA -3.88, OA decreasing strength? 1.23, and MA -3.40. Which list has the conjugate bases of these acids in order of a. lactate> oxalate >malate b. oxalate > malate> lactate c. lactate> malate > oxalate d. c. oxalate > lactate > malate malate > lactate> oxalate 49. What is the pH of a 0.20 M solution of cubaramine? The K, value for jaspersamine is 2.s x 10 50. What is the pH of a 0.10 M solution of trimethylamine (pk, 4.13)?Explanation / Answer
Ans 45 ) Kb stands for base ionization constant.
Sodium phosphate is a base with chemical formula Na3 PO4
Sodium phosphate are produced by acid base reaction between phosphoric acid and sodium hydroxide.
Then the overall final equation becomes :
H3 PO4 + 3NaOH ----------- Na3 PO4 + 3H2 O
We can also write a reversible reaction of base acting as a base by accepting proton from water.
Therefore, Kb = [H3PO4][OH- ][Na+ ] / [Na3 PO4 - ] Ans.
Ans 46 ) H3PO4 + NaOH + H2O ------ NaH2 PO4 + 2H2O.
Therefore, Kb for sodium dihydrogen phosphate =[H3PO4][Na+ ][OH- ]/ [NaH2 PO4 ]
Ans 47 ) a) decreasing order of base strength Answer -- a ) is the correct .
Kb for CN- is the maximum followed by NO2- and last is F-. Ka given in the question is just the reverse. This conclusion is because Ka = [H3O+][A-]/[HA] ; Whereas Kb = [HA][OH-]/[A-].
Ans 48) pKa = - log (Ka)
Solving for Ka from given pKa data we get Ka for lactic acid = 1.3 * 10^-4
Ka for oxalic acid = 5.9 * 10^-2 and Ka for Malic acid = 3.9 * 10^-4.
So strongest acid is OA followed by MA and then LA.
So strongest bases in decreasing order Lactate>malate>oxalate.
HENCE OPTION c. is the correct answer.