CH 101/Exercises 10
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Arrhenius bases: the hydroxides
The definition of what a base is has undergone quite a remarkable development. For Arrhenius a base was anything that could produce hydroxyl ions OH- in aqueous solution'
That brings us to hydroxides, with a generic formula M(OH)x (x=1,2,3,..)
They are typically
- solids
- with a pretty high melting point
- they fall under rule 5 of the solubility rules: "other"
This means that most hydroxides, except those of e.g. Na, K, etc. are poorly soluble or worse. Or in other words they have a rather small solubility product, the constant that describes the equilibrium that arises when water is brought in contact with an excess of solid hydroxide.
Excercises
An excess of the sparingly soluble solid barium hydroxide Ba(OH)2 is allowed to equilibrate with water at room temperature. Under these conditions the solubility product Ksp= 4.10-18
- Write a balanced chemical equation for the equilibrium
- Write the expression for Ksp in terms of the concentrations.
- Calculate the [Ba2+] as well as the [OH-] of the resulting solution
- What is the pH of the solution.