Worksheet: Polyprotic Acid Dissociation

In this worksheet, we will practice calculating concentrations of species for polyprotic acids, where multiple equilibria exist.

Q1:

Hydrogen telluride (HTe)2 is a diprotic acid with 𝐾=2.3×10a1 and 𝐾=1.3×10a2. For a 0.1 M solution of HTe2, approximately how many orders of magnitude lower is the change in [HTe]2– caused by the second dissociation relative to that caused by the first dissociation?

  • A1
  • B3
  • C10
  • D15
  • E6

Q2:

Nicotine is a base that can accept a maximum of two protons, with 𝐾a values of 7.0×10 and 1.4×10. The initial concentration of nicotine in an aqueous solution is 0.050 M.

Calculate [CHNH]10142+.

  • A 6 . 0 × 1 0   M
  • B 1 . 9 × 1 0   M
  • C 3 . 5 × 1 0   M
  • D 9 . 9 × 1 0   M
  • E 1 . 9 × 1 0   M

Calculate [CHNH]1014222+.

  • A 1 . 5 × 1 0   M
  • B 4 . 5 × 1 0   M
  • C 1 . 4 × 1 0    M
  • D 5 . 7 × 1 0   M
  • E 8 . 0 × 1 0   M

Q3:

Soda water (carbonated water) is a solution of carbon dioxide in water. The solution is acidic because CO2 reacts with water to form carbonic acid, HCO23. HCO()+HO()HO()+HCO()HCO()+HO()HO()+CO()2323+3–a3–23+32–aaqlaqaqaqlaqaq,𝐾=4.3×10,𝐾=5.6×10 In a saturated solution of CO2, [HCO]23 is initially 0.033 M before dissociation takes place.

Calculate [H]+ at equilibrium.

  • A 6 . 2 × 1 0   M
  • B 8 . 5 × 1 0   M
  • C 1 . 4 × 1 0   M
  • D 6 . 1 × 1 0   M
  • E 1 . 2 × 1 0   M

Calculate [CO]32– at equilibrium.

  • A 5 . 1 × 1 0    M
  • B 1 . 2 × 1 0   M
  • C 5 . 6 × 1 0    M
  • D 5 . 6 × 1 0    M
  • E 6 . 0 × 1 0   M

Q4:

Calculate the value of [CH(CO)]64222– in a 0.010 M solution of phthalic acid, CH(COH)6422.

  • A 3 . 6 × 1 0 − 6 M
  • B 3 . 9 × 1 0 − 6 M
  • C 1 . 1 × 1 0 − 3 M
  • D 2 . 8 × 1 0 − 3 M
  • E 7 . 2 × 1 0 − 2 M

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