Worksheet: Autoionization of Water

In this worksheet, we will practice calculating the autoionization constant of water from concentrations of hydronium and hydroxide ions.

Q1:

The ionization constant of water (𝐾)w is 9.311×10 at 60∘C. To 4 significant figures, what is the value of [HO]3+ in pure water at this temperature?

  • A 9 . 3 1 1 × 1 0    M
  • B 3 . 0 5 1 × 1 0   M
  • C 4 . 6 5 6 × 1 0    M
  • D 4 . 0 9 6 × 1 0   M
  • E 2 . 2 7 3 × 1 0   M

Q2:

Why is a sample of pure water at 40∘C neutral even though [HO]=M3+1.7×10?

The self-ionization constant of water, 𝐾w, is 2.9×10 at 40∘C.

  • AThe concentrations of HO3+ and OH– ions are exactly equal.
  • BWater loses its acidity when heated.
  • C H O 3 + molecules cannot be deprotonated.
  • DThe concentration of OH– ions is greater than that of HO3+ ions.
  • E 𝐾 w is higher at 40∘C than at 25∘C.

Q3:

The ionic product of water at 80∘C is 2.4×10. What is the concentration of hydroxide ions in pure water at 80∘C? Give your answer to two significant figures.

  • A 1 . 0 × 1 0    M
  • B 4 . 9 × 1 0   M
  • C 3 . 5 × 1 0   M
  • D 2 . 4 × 1 0    M
  • E 1 . 2 × 1 0    M

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