Solubility Product Constant

For the equilibria between an ionic solid and its dissolved ions, the equilibrium constant is called the solubility product K_sp.

K_sp gives us information about the solubility of the compound. The lower K_sp is, the less soluble a compound is.

Eg: CuCl₂ K_sp=1.7×10^-7 at 25°C        NaCl K_sp= 3.8×10¹ at 25°C      CuS K_sp=6.0×10^-37 at 25°C

Solubility: The concentration of a dissolved solid in g/100mL. If stated in M is called molar solubility.

Calculating K_sp from solubility

Calculate solubility using K_sp

Predicting Precipitation:

The reaction quotient can tell us whether a compound will form a precipitate or not by comparing it to K_sp.

• If Q = K the solution is saturated and there should be no precipitate formed
• If Q < K, the solution is unsaturated and there should be no precipitate formed
• If Q > K, the solution is supersaturated and the equilibrium will shift to the left to reduce the amount of products, creating a precipitate

Ex: if 100 mL of 0.100 M calcium chloride are mixed with 100 mL of 0.0400 M sodium sulfate at 20°C, will a precipitate form? Hint, the K_sp of calcium sulfate is 3.6×10^-5 at 20°C.

Since Q > K, a precipitate will form.

William Anderson (Schoolworkhelper Editorial Team)

William completed his Bachelor of Science and Master of Arts in 2013. He current serves as a lecturer, tutor and freelance writer. In his spare time, he enjoys reading, walking his dog and parasailing. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0

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