The next 8 questions refer to the following descriptions of chemical solutions.
ID: 948012 • Letter: T
Question
The next 8 questions refer to the following descriptions of chemical solutions. a solution with pH = 7 a solution with pH 7 which is a buffer Ionization constants HCOOH Ka=1.8 x l0- 4 CH3NH2 Kb = 4.4 x 10 -4 H3PO3 Kal = 3 x 10 -2 Ka2 = 1.7 X 10-7 (Contrary to the appearance of its formula. phosphorous acid is diprotic, not diprotic.) A solution with an initial KCOOH concentration of 1 M and an initial K2HPO3 concentration of 1 M. Equal volumes of both solutions mixed together. A solution with an initial H3PO3 concentration of 1 M and an initial KH2PO3 concentration of 1 M. Equal volumes of both solutions mixed together. a solution with an initial CH3NH2 concentration of 1 M and an initial CH3NH3C1 concentration of 1 M. Equal volumes of both solutions mixed together.Explanation / Answer
1: Here we are adding equal volume and equal concentration of KCOOH and K2HPO3.
KCOOH is a salt of weak conjugate base COOH-. K2HPO3 is also a salt of the weak conjugate base HPO32- . Since both COOH- and HPO32- are conjugate bases they will not form any buffer solution. Hence pH is the solution is greater than 7 due to salt hydrolysis to form hydroxide ion.
Hence this is a solution with pH > 7 and doesn't form a buffer solution. Hence option (D) is correct.
2: Here we are adding equal volume and equal concentration of H3PO3 and KH2PO3. KH2PO3 is completely dissociated to give weak conjugate base H2PO3- . H2PO3- is conjugate base of weak acid H3PO3. Since H2PO3- and H3PO3 are conjugate acid - base pair, they form an acidic buffer solution. The pH of the solution will be less than 7
Hence option (C) is correct.
3: Here we are adding equal volume and equal concentration of CH3NH2 and CH3NH3Cl. CH3NH2 is a weak base. CH3NH3Cl is completely dissociated to give conjugate acid CH3NH3+ of the weak base CH3NH2. Hence the weak base CH3NH2 and conjugate acid CH3NH3+ will form a basic buffer with pH greater than 7.
Hence option (E) is correct.
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