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+.

  • A6.0×10 M
  • B1.9×10 M
  • C3.5×10 M
  • D9.9×10 M
  • E1.9×10 M

Calculate [CHNH]1014222+.

  • A1.5×10 M
  • B4.5×10 M
  • C1.4×10 M
  • D5.7×10 M
  • E8.0×10 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.

  • A6.2×10 M
  • B8.5×10 M
  • C1.4×10 M
  • D6.1×10 M
  • E1.2×10 M

Calculate [CO]32– at equilibrium.

  • A5.1×10 M
  • B1.2×10 M
  • C5.6×10 M
  • D5.6×10 M
  • E6.0×10 M

Q4:

Calculate the value of [CH(CO)]64222– in a 0.010 M solution of phthalic acid, CH(COH)6422. CH(COH)()+HO()HO()+CH(COH)(CO)()CH(COH)(CO)()+HO()HO()+CH(CO)()642223+6422–a6422–23+64222–aaqlaqaqaqlaqaq,𝐾=1.1×10,𝐾=3.9×10

  • A3.6×10 M
  • B2.8×10 M
  • C3.9×10 M
  • D7.2×10 M
  • E1.1×10 M

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