4. You add solid calcium oxalate to 1 L of water until some solid remains at the

Question

4. You add solid calcium oxalate to 1 L of water until some solid remains at the bottom of the beaker. The Ksp of calcium oxalate is 2.3 x 109 a. In the large circle to the right, draw a picture that represents the concentration of ions in solution (use .'s and x's to simplify the picture). Each and x should represent -1 x 10s M for that ion. (Note that this is representing concentration, not individual ions.) Show your work below. b. You add 100 mL water (to the beaker in 4a). Some solid remains at the bottom of the beaker. DO NOT perform a calculation. Draw a picture that represents the solid at the bottom of the beaker and the concentration of ions in solution once the system re-establishes equilibrium. Describe your reasoning. c. d. Pre-Recitation 8- Page 1 of 4

Explanation / Answer

The equation for dissociation of calcium oxalate is CaC2O4 --> Ca2+ + C2O42-

The Ksp= [Ca2+][C2O4]

If we take the concentration of Ca2+ as x the C2O4 also will be x

so Ksp= x^2 which will give 2.3x10^-9= x^2 and x= 4.8 x 10^-5 or approximately 5 x 10^-5

So we need to draw five calcium ions (dots) five oxalate ions (cross ) in the beaker

Once 100ml of water is added some part of undissolved particle will come in the solution. So the number of calcium ions and oxalate ions will increase.  

The reason for the observation is, once the water is added the concentration of ions in the solution will reduce But Ksp should be maintained as constant. In order to maintain it as constant the number of ions in solution also will increase so that the concenration remains constant.

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