Question

1A) How will the calculated Ksp value of Ca(OH)2 be affected if the original Ca(OH)2 solution is not saturated? Explain?

B) Does adding distilled water to the titrating flask in order to wash the sides of the flask and the buret tip affect the computed Ksp of Ca(OH)2? Explain?

C) How might tap water instead of distilled water affect the calculated Ksp of Ca(OH)2? Explain?

D) The temperature of the solution was 21.1 degrees Celcius. Is the molar solubility of a salt temperature dependent? Explain?

Answer 1

A). If the Ca(OH)2 solution is not saturated, that means that more could be added that would still dissolve. If you measure the added quantity and use that to calculate Ksp, the value will be lower than expected, since the true solubility is higher.

B) Adding distilled water will dilute the solution, allowing more Ca(OH)2 to dissolve. Thus, if the calculations are performed without taking this amount into consideration, the precipitate will weigh less, and the apparent Ksp will be higher than the true value.

C) Tap water may contain traces of Ca2+ ions, or the pH may be higher or lower than 7. By the common ion effect, the presence of Ca ions will result in a smaller Ksp value measured. Similarly, if the pH is greater than 7 the measure Ksp will be too low, and if it is below 7, the measure Ksp will be too high (since H+ ions react with OH- ions to make water.

D) As temperature changes, the average speed of water molecules in a solution changes (the warmer the temperature, the faster they are). This affects their ability to solvate ions, and thus Ksp values tend to be fairly dependent on temperature. In most (but not all) cases, compounds are more soluble at higher temperatures.

Answer 2

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