Chemistry 30
Unit 4: Solutions
Assignment 4 - The Solubility Product Constant, Ksp

1.	Write the balanced equation and the solubility product constant expression, Ksp, for the each of the following dissociation reactions. All compounds are solids.  One has been given as an example.

	An important reminder – the seven diatomic molecules (H2, N2, O2, F2, Cl2, Br2, I2) ARE NOT diatomic as ions!

	Reminders	– ion charges MUST BE included.
				– solids (and liquids) are NOT included in the equilibrium expression
				– don’t forget to include exponents when needed 
				– polyatomic ions (e.g. CO3-) do not break apart

Compound	Equation	Ksp	
(NH4)2S	(NH4)2O (s) 2 NH4 +(aq) +  S2-(aq)	Ksp = [NH4+]2[S2-]	
CaS			
K2SO4			
Mg(OH)2			

2.	Consider the Ksp values for the following substances, all measured at 25C  

PbCrO4	2.0  10-16	
PbSO4	1.3  10-8	
PbCO3	7.4  10-14	
	
	Which substance is MOST soluble (dissolves the best)	_____________________

	Which substances is LEAST soluble (dissolves the worst) _____________________

3.	Solutions are prepared by dissolving a sulfate salt (an ionic compound containing the sulfate ion) in water.   Which one of the compounds listed would we use in order to get the highest concentration of sulfate ion, SO42-?

	(a salt is an ionic compound that contains a positive ion other than hydrogen and a negative ion other than hydroxide).

	A.	CaSO4	Ksp = 2.6  10-4
	B.	SrSO4		Ksp = 7.6  10-7
	C.	BaSO4	Ksp = 1.5  10-9
	D.	RaSO4	Ksp = 4.0  10-11

4.	Calculate Ksp for a saturated nickel(II) sulfide, NiS, solution with a molar concentration of 3.27  10-11

	Begin with a balanced dissociation equation:

	From information provided in the question and the balanced equation, determine the concentration of the ions Ni2+ and S2-:

	Write the Ksp expression for this reaction:

	Substitute values into the equation and solve for the unknown, Ksp:

5.	At 25C, the concentration of Ce(OH)3 in a saturated solution is 5.1  10-6 M.  Calculate Ksp.

	Begin with a balanced equation:

	Determine the concentration of the ions in the solution. Be careful with [OH-].

	Write the Ksp expression, then substitute values into the equation and solve for the unknown, Ksp.

 

6.	Calculate the concentration of ions in a saturated solution of CaCO3 in water at 25C.  Ksp for CaCO3 is 4.8  10-9.