Question

A solution contains 1.91×10^-2 M calcium nitrate and 1.91×10^-2 M cobalt(II) acetate. Solid sodium hydroxide is added slowly to this mixture. What is the concentration of cobalt(II) ion when calcium ion begins to precipitate? Solubility product constant data is found in the Chemistry References.

[Co²⁺] = _____ M

Answer 1

Ksp of Ca(OH)2 = 5.5*10^-6

Ca(OH) 2 →Ca+2 + 2 (OH) -

so solubility product   = conc of Ca+2 * (conc (OH)- ^2     ------1)

                   Let solid NaOH added to solution makes it to be 1 M in NaOH

It gives 1 M OH - ions

Putting these values in (1) ,

we get    5..5 *10^-6 = conc of Ca+2   * 1

So conc of Ca+2 =   5.5 *10^-6M