Worksheet: Autoionization of Water

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


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?

  • A9.311×10 M
  • B3.051×10 M
  • C4.656×10 M
  • D4.096×10 M
  • E2.273×10 M


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.
  • CHO3+ molecules cannot be deprotonated.
  • DThe concentration of OH– ions is greater than that of HO3+ ions.
  • E𝐾w is higher at 40∘C than at 25∘C.


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.

  • A1.0×10 M
  • B4.9×10 M
  • C3.5×10 M
  • D2.4×10 M
  • E1.2×10 M

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