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Worksheet: Autoionization of Water

Q1:

The ionization constant for water ( 𝐾 ) w is 9 . 3 1 1 Γ— 1 0 βˆ’ 1 4 at 6 0 ∘ C . To 4 significant figures, what is the value of [ H O ] 3 + in pure water at this temperature?

  • A 4 . 6 5 6 Γ— 1 0 βˆ’ 1 4 M
  • B 9 . 3 1 1 Γ— 1 0 βˆ’ 1 4 M
  • C 2 . 2 7 3 Γ— 1 0 βˆ’ 6 M
  • D 3 . 0 5 1 Γ— 1 0 βˆ’ 7 M
  • E 4 . 0 9 6 Γ— 1 0 βˆ’ 8 M

Q2:

Why is a sample of pure water at 4 0 ∘ C neutral even though [ H O ] M 3 + = 1 . 7 Γ— 1 0 βˆ’ 7 ?

The self-ionization constant of water, 𝐾 w , is 2 . 9 Γ— 1 0 βˆ’ 1 4 at 4 0 ∘ C .

  • A 𝐾 w is higher at 4 0 ∘ C than at 2 5 ∘ C .
  • BWater loses its acidity when heated.
  • CThe concentration of O H – ions is greater than that of H O 3 + ions.
  • DThe concentrations of H O 3 + and O H – ions are exactly equal.
  • E H O 3 + molecules cannot be deprotonated.

Q3:

The ionic product of water at 8 0 ∘ C is 2 . 4 Γ— 1 0 βˆ’ 1 3 . What is the concentration of hydroxide ions in pure water at 8 0 ∘ C ?

  • A 1 . 0 Γ— 1 0 βˆ’ 1 4 M
  • B 2 . 4 Γ— 1 0 βˆ’ 1 3 M
  • C 1 . 2 Γ— 1 0 βˆ’ 1 3 M
  • D 4 . 9 Γ— 1 0 βˆ’ 7 M
  • E 3 . 5 Γ— 1 0 βˆ’ 7 M