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Organic Chemistry - Calculating Molar Solubility

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6. Calculate the molar solubility of Mg(OII)_2 in a solution with a pH of 12.8 (K_op of Mg(OH)^2 is 1.2 * 10^-11

7. For a reaction to be spontaneous at any temperature, which one of the following is true:
a) [delta] H is positive and [delta] S is positive
b) [delta] H is positive and [delta] S is negative
c) [delta] H is negative and [delta] S is negative

8. Which one of the following solutions can act as a buffer?
a) Nat/HI
b) NaOH/NaCI

9. A student is asked to prepare a buffer solution at pH = 3.6, which one of the following weak acids should be used?
a) NH_4CI (K_b = 1.8 * 10^-5 for NH_4OH
b) HA (K_a = 2.7 * 10 ^-4)
c) HB (K_a = 1.5 * 10^-9)
d) HC (K_a = 5.3 * 10^-13)

10. Which one of the following statements is false?
In the equilibrium Mg(OH)_ (s) ---Mg^2+ (aq) + 2OH(aq)
a) The reaction moves forward when adding in acid
b) The reaction moves backward when adding in solid NaCl
c) The reaction moves backward when adding in solid MgCl^2
d) The reaction moves forward when adding in water

11. Acetic acid, CH_3COOH is a weak acid (K_a - 1.8 * 10 ^-5)
a) Solution A is 100ml of 0.10M acetic acid
b) Solution B is prepared by adding 0.0050 mol solid NaOH to Solution A
c) Solution C is prepared by adding 0.010 mol solid NaOH to Solution A
d) Solution D is made by adding 0.0150 mil solid NaOH into Solution A
e) Calculate the pH for each of the solutions, A,B,C, and D

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Solution Summary

The molar solubility is calculated for organic chemistry. The expert determines if the reaction is spontaneous at any temperature.

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6. Mg(OH)2 -> Mg2+ + 2OH-
As pH = 12.8, pOH = 1.2 which means [OH-] = 10-1.2 = 0.063 M
If 's' is the molar solubility,
Ksp = (s)(2s + 0.063)2 = 1.2 x 10-11
As molar solubility will be really small compared to 0.063, hence 2s + 0.063 = 0.063 approximately
Hence, s(0.063)2 = 1.2 x 10-11
Solving for molar solubility, s = 3 x 10-9 M

7. [delta] G = [delta] H - T[delta] S
For spontaneity, [delta] G must be negative. This is possible at all T if [delta] H is negative and ...

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