Chemistry (7th Edition)

Published by Pearson
ISBN 10: 0321943171
ISBN 13: 978-0-32194-317-0

Chapter 14 - Chemical Equilibrium - Worked Example - Page 565: 12


The equilibrium constant for this reaction is equal to: $K_c = 1.80 \times 10^{-11}$

Work Step by Step

The dissolution of solid magnesium hydroxide in water is described by this reaction: $Mg(OH)_2(s) \lt -- \gt Mg^{2+}(aq) + OH^-(aq)$ Balancing the reaction: $Mg(OH)_2(s) \lt -- \gt Mg^{2+}(aq) +2 OH^-(aq)$ Now write the $K_c$, you just need to put the concentrations of the products divided by the concentrations of the reactants. ** Remember: For $K_c$, pure solids (s) and liquids(l) are omited in the expression. So, in this case, $Mg(OH)_2(s)$ will not appear. ** The balanced coefficients are the exponents of the concentrations of their respective compounds: $K_c = \frac{[Products]}{[Reactants]} = \frac{[Mg^{2+}][OH^-]^2}{1} = (1.65 \times 10^{-4})(3.30 \times 10^{-4})^2 = 1.80 \times 10^{-11}$
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