6- 0.012 moles of sodium sulphate are added to 400 ml of each of two solutions.
ID: 589647 • Letter: 6
Question
6- 0.012 moles of sodium sulphate are added to 400 ml of each of two solutions. One solution contains 1.5 x 10-3M barium chloride; the other contains 1.5 x 103M calcium chloride. Given that Ksp for barium sulphate = 1.5 x 10-9 and Ksp for calcium sulphate = 6.1 x 10-5 Which of the following is true? a) Barium sulphate would precipitate but calcium sulphate would not b) calcium sulphate would precipitate but barium sulphate would not c) Both barium sulphate and calcium sulphate would precipitate d) Neither barium sulphate nor calcium sulphate would precipitate e) Not enough information is given to determine if precipitation would occur.Explanation / Answer
OPTION A. Solubility product is the equilibrium constant for equilibrium between concentration of dissolved salt to the precipitated salt in case of a partially soluble or insoluble salt in water. Given that 0.012M of sodium sulphate is added to both the solutions, we can determine that the concentration of sulphate added to each calcium and barium solution is 0.012M while the concentration of barium and calcium is drastically lower than 0.012M. Therefore, the concentrations of barium and calcium ions in the medium are the limiting factors and so there will only be 0.0015M barium sulphate and calcium sulphate in the medium.
The Ksp of barium sulphate can be expressed as Ksp = [Ba2+][SO42-]/[BaSO4] which can be substituted as 1.5x10-9 = [Ba2+][SO42-]/1 to find the molar solubility of BaSO4, which is the molarity of barium sulphate soluble in water. Since the concentration of barium and sulphate ions in dissolved barium sulphate will be in a 1:1 ratio, the molar solubility of the salt can be written as 1.5x10-9 = x2 where x gives the concentration of dissolved salt. Thus we can get the molar solubility of the salt as 3.8729x10-5M implying that the maximum concentration of dissolved barium sulphate in water can be 3.8729x10-5M while there exists 1.5x10-3M. which is nearly 50 times more than what can be dissolved So we can say that barium sulphate will precipiate out.
Similarly, from the Ksp of calcium sulphate, its molar solubility is calculated as 6.1x10-5 = 0.0015 = x2 where x gives the concentration of dissolved salt giving the maximum concentration of dissolved barium sulphate in water can be 7.8102x10-3M while there exists only 1.5x10-3M calcium sulphate is present in the medium leaving it completely dissolved.
Therefore, it can be concluded that in the two solutions, only barium sulphate will precipitate while calcium sulphate will not.
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