AP Chemistry - Solutions Review

Chem I | Chem II AP
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1)
List the three things that must happen in the solution process. Label the processes ΔHsolute, ΔHsolvent & ΔHhydration. Is energy gained or lost during those processes?
2)
Why do ionic solutes dissolve in polar solvents but not in nonpolar solvent?
3)
Draw water molecules around the substance below to show how the molecule will dissolve.
There should be water molecules around every hydrogen bonding site with the hydrogen in the water attracted to the oxygen in the molecule and the oxygen in the water attracted to the hydrogen in the molecule.
4)
A solute dissolves in a solvent exothermically until the solution is saturated. What will happen if:
a. The Solution is stirred:
b. The solution is heated:
c. More Solute is added:
d. More Solvent is added:
e. The pressure above the solution is increased:
On section a, the solution is already saturated, so stirring will not do anything.
On section b, since this is an exothermic dissolving process, heating will make it supersaturated. For endothermic processes, heating will make it unsaturated.
On section c, since the solution is already saturated, adding more solute will do nothing.
On section d, adding more solvent will dilute the solution or make it more unsaturated.
On section e, if there is a gas solute, then the solution will become unsaturated. If the solute is a solid or liquid, nothing will happen.
5)
Describe how IMF influences
a. Chromatography
b. Distillation
c. Filtration
d. Evaporation
6)
Using the solubility graph, how can you tell if a solution is
a. Saturated
b. Unsaturated
c. Supersaturated

If the solution is saturated, the graph will show a point on or above the line. Any extra solute above the saturated line will be sitting at the bottom of the container, undissolved.

If the solution is unsaturated, the graph will show a point below the line.

If the solution is supersaturated, you cannot tell from the graph alone without additional information telling whether or not the additional solute is dissolved. To determine from the graph supersatured, there has to be a point above the line and information saying that all additional solute is dissolved.

7)
Classify as to suspension, colloid or solution.
a. Homogenous, transparent
b. Particle size ranges from 1-1000 nm; Tyndall effect
c. Particles settle out due to gravity; can be separated by filtration
d. No Tyndall effect; cannot be separated by filtration
8)
How many grams of calcium hydroxide are needed to make 100.0 mL of 250.0 mL of solution
g
100 mL x
1 L
1000 mL
= 0.10 L
0.25 M =
x mol
0.10 L
x = 0.025 mol Ca(OH)2
0.025 mol Ca(OH)2 x
74.1 g Ca(OH)2
1 mol Ca(OH)2
= 1.85 g Ca(OH)2
9)
What is the molarity of a solution containing 12.0g of sodium hydroxide in 250.0 mL of solution
M
12.0 g NaOH x
1 mol
40.0 g NaOH
= 0.30 mol
0.30 mol
0.25 L
= 1.20 M
10)
If you dilute 175 mL of a 1.6 M solution of lithium chloride to 1.0 L, determine the new concentration of the solution
M
M1V1 = M2V2
(1.6 M)(0.175 L) = (x M)(1.0 L)x = 0.28 M
11)
To 2.00 L of 0.445 M HCl, you add 3.88 L of a second HCl solution of an unknown concentration. The resulting solution is 0.974 M. Assuming the volumes are additive, calculate the molarity of the second HCl solution
M
Initial solutions
2.00 L of 0.445 M HCl = (0.445 M)(2 L) = 0.089 mol HCl
3.88 L of ? M
Final Solution
5.88 L of 0.974 M HCl = (0.974 M)(5.88 L) = 5.727 mol total
To find missing solution:
5.727 mol total - 0.089 mol from 1st solution = 4.837 mol from 2nd solution
4.837 mol
3.88 L
= 1.25 M
12)
What is the mole fraction of cinnamic acid in a mixture that is 50.0% weight urea in cinnamic acid ( urea= 60.06 g/mol; cinnamic acid= 148.16 g/mol)
50% of each solution means that they each have the same mass. I will solve it with 50 g of each, but you will get the same answer with 1 g of each or any other number that has the same mass ratio.
50 g urea x
1 mol
60.06 g
= 0.8325 mol
50 g cinnamic acid x
1 mol
148.16 g
= 0.3375 mol
Add to get the total moles: 0.8325 mol + 0.3375 mol = 1.170 mol total
Χcinnamic acid =
0.3375 mol cinnamic acid
1.170 mol total
= 0.288
Remember that mole fraction does not have a unit.
13)
How many grams of water must be used to dissolve 100.0 grams of sucrose (C12H22O11) to prepare a 0.020 mole fraction of sucrose in the solution?
g
100.0 g sucrose x
1 mol
342.0 g
= 0.292 mol
0.020 =
0.29 mol sucrose
x mol total
x = 14.62 mol total
To find moles of water: 1.62 mol total - 0.292 mol sucrose = 14.32 mol water
14.32 mol x
18.0 g
1 mol
= 257.9 g = 260 g
14)
A solution with a concentration of .14 M is measured to have an absorbance of 0.43. Another solution of the same chemical is measured under the same conditions and has an absorbance of 0.37. What is its concentration?
M
This is just a direct proportion since Absorbance changes directly with concentration
0.43
0.14 M
=
0.37
x M
x = 0.12 M
15)
The absorptivity of a particular chemical is 1.5/ M˙cm. What is the concentration of a solution made from this chemical if a 2.0 cm sample had an absorbance of 1.20?
M
A = abc
1.20 = (1.5 M-1cm-1)(2.0 cm)(x M)x = 0.40 M