Chem 12

Solubility Review Answers

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1. Describe the relationship between the rate of dissolving solid and rate of crystallization for:

a) a saturated solution and some solid The rate of dissolving=the rate of crystalization

b) an unsaturated solution and some solid The rate of dissolving>the rate of crystalization

c) a supersaturated solution The rate of dissolving<the rate of crystalization

2. Write the equilibrium expression and Ksp equation for Fe2O3 .

Fe2O3(s) <----> 2Fe+3 + 3O-2 Ksp = [ Fe+3]2[ O-2 ]3

3. Write the net ionic equation for the reaction between Al(NO3)3 and Na2CO3.

2Al+3 + 3CO3-2 ------------> Al2(CO3)3(s) The two are reversed.

4. Mg+2, Sr+2, Ca+2 and Be+2 are possibly in a solution. The solution reacts with Na2SO4 but not NaOH or Na2S. What cations are in the solution? Sr+2

5. A solution contains SO4-2 or OH- or both. It reacts with Zn(NO3)2and Sr(NO3)2, What anions are in the solution? Both are in the solution or it would not have reacted with each solution.

6. Ag2CO3(s) ⇄ 2Ag+ + CO3-2 Describe the effect on the solubility of Ag2CO3 for each change below:

a) Add Ag2CO3 nothing

b) Add water nothing

c) Add NaCl increases

d) Add Pb(NO3)2 increases

e) Add Na2CO3 decreases

f) Add AgNO3 decreases .

7. If the trial Ksp = 1.7x10-7 and the Ksp = 3.8x10-7 will a precipitate occur?

Trial Ksp < Ksp No ppt.

8. For a saturated solution of Fe(OH)3 the [OH-] is found to be 1.3x10-4M. Calculate the [Fe+3] and the solubility of the salt in mols/L.

4.3 x10-5M

 

9. Consider the equilibrium that exists in a saturated solution of PbCl2. Write the equilibrium expression.

PbCl2(s) <-----> Pb+2 + 2Cl-

If the equilibrium shifts to the right, what affect does this have on the solubility? Increases

Describe how the addition of each of the following will affect the solubility of PbCl2.

a) AgNO3        increases

b) NaCl            decreases

c) Na2S            increases

d) H2O             nothing

e) NaNO3        nothing

f) Pb(NO3)2      decreases

g) Beer             nothing

10. If the reaction is endothermic, how does the Ksp and the solubility change if the temperature is increased?

Shifts right and the Ksp increases

1. In a titration 250ml of a .200M AgNO3 solution was used to precipitate out all of the Cl- in a 500 ml sample. Calculate [Cl-].

0.100M

2. In a titration 26.5ml of .100M Pb(NO3)2 was used to precipitate out all of the I- in a 3.00ml sample of water. Calculate [I-].

1.77M

3. Co(OH)2 Solubility = 3.0x10-3 g/L Ksp=?

1.3 x 10-13

4. Ag2C2O4 Solubility = 8.3x10-4 M Ksp=?

2.3 x 10-9

 

5. SrF2 Ksp = 2.8 x 10-9 Solubility in (M) = ?

8.9 x 10-4 M

6. Cu(IO3)2 Ksp = 1.4 x 10-7 Solubility (g/L) = ?

1.4 g/L

7. Calculate the maximum concentration of OH- that can exist in a .200M Ca(N03)2 solution. Ksp (Ca(OH)2) = 2.8 x 10-8

3.7 x 10-4M

8. Calculate the maximum concentration of CO3-2 that can exist in a .500M Fe(NO3)3 solution.

Ksp (Fe2(CO3)3) = 2.8 x 10-14

4.8 x 10-5M

9. Will a precipitate form if 200ml .0020M Mg(NO3)2 is mixed 300ml of .0030M NaOH?

 Trial ksp = 2.6 x 10-9 > 5.6  x  10-12 and ppt.

10. Will a precipitate form if 25.0ml of .0020M Pb(NO3)2 is mixed with 25.0ml of .040M NaBr.

Trial ksp =4 x 10-7 < 6.6   x  10-6 and no ppt.

11. 20.0 g of PbCl2 is placed in 2.0 L of water. Some but not all dissolves to form a saturated solution. How many grams do not dissolve?

                        PbCl2(s)  ⇄       Pb2+     +          2Cl-

                        x                      x                      2x

                        1.2  x  10-5       =          4x3

                        x          =          1.44  x  10-2 M

                        2.0 L    x   0.00144  mole   x   278.2 g            =          8.0 g    dissolves         20.0  -  8.0  =  12.0g does not dissolve

                                                            L          mole