Kidney stones are composed of crystals of calcium oxalate, CaC2O4. The solubility of CaC2O4 is
6.7 x 10-5 g per 100 ml of solution. What is the pH of a saturated solution of calcium oxalate? (Molar masses of Ca, C and O are 40.0 g/mol, 12 g/mol, 16 g/mol respectively.)
Thank you for your help in advance.
I am doing a lab report involving limiting reactants and percent compostition. The reactans are calcium chloride dihydrate and potassium oxalate monohydrate, which yeilds calcium oxalate monohydrate. My question is which product should i choose as my varied amount when doing my experiment that will yeild the best results of calcium oxalate monohydrate?
To find the pH of a saturated solution of calcium oxalate, we need to calculate the concentration of hydroxide ions (OH-) in the solution.
The solubility of CaC2O4 is given as 6.7 x 10^-5 g per 100 ml of solution. We can convert this to mol/L by dividing by the molar mass of CaC2O4 (40.0 + 12 + (16 x 4) = 128.0 g/mol) and multiplying by 1000 (to convert mL to L).
So, the solubility of CaC2O4 in mol/L is:
(6.7 x 10^-5 g / 100 mL) * (1 mol / 128.0 g) * (1000 mL / 1 L) = 5.234 x 10^-7 mol/L
Since calcium oxalate (CaC2O4) is a sparingly soluble salt, it dissociates in water to release calcium ions (Ca2+) and oxalate ions (C2O4^-2). This means the concentration of Ca2+ and C2O4^-2 ions in the saturated solution will be equal.
Therefore, the concentration of Ca2+ ions (and C2O4^-2 ions) in the saturated solution is:
5.234 x 10^-7 mol/L
Now, to find the concentration of hydroxide ions (OH-) in the solution, we need to consider the dissociation of water. Water molecules can undergo autoionization to produce equal concentrations of hydrogen ions (H+) and hydroxide ions (OH-). In pure water, the concentration of H+ and OH- ions are both 1 x 10^-7 mol/L.
Since the Ca2+ ions will react with the OH- ions to form a precipitate of Ca(OH)2, we can assume that the OH- ions from water will be completely consumed by the Ca2+ ions. Therefore, the concentration of OH- ions in the saturated solution will be equal to the concentration of Ca2+ ions.
Now, we can calculate the pOH of the saturated solution:
pOH = -log[OH-] = -log(5.234 x 10^-7) ≈ 6.28
Finally, we can find the pH of the saturated solution using the relationship:
pH + pOH = 14
pH + 6.28 = 14
pH ≈ 7.72
Therefore, the pH of a saturated solution of calcium oxalate is approximately 7.72.