Experiment 12 – Solutions, Solubility, and Mass Percent
Name __________________
Lab Section __________________
Experiment 12 – Solutions, Solubility, and Mass Percent
Introduction
A solution is a homogeneous mixture of a solute in a solvent. A solute is the thing being
dissolved, and the solvent is the thing doing the dissolving. In general, the solute is the smaller
amount of the two. The determining factor in whether or not a solution can be made between a
given solute and solvent is determined by the intermolecular forces of the two. If the solute is
polar and the solvent is polar, a solution will be formed if the two are added. Likewise, this will
occur if both are nonpolar. This is commonly referred to as the “like dissolves like” rule.
If a solid dissolves in a liquid, it is said to be soluble. If it does not, it is insoluble. A different
term is used, however, when describing liquids. If one liquid is able to be dissolved into another,
it is referred to as miscible. It if will not mix, it is immiscible. Some refer to “mixable as
miscible” to remember this.
There is a limit to how much solid will dissolve into a liquid. This is referred to as its saturation.
There are three types of solution. Undersaturated is where more solute can be added to the
solution. Saturated means that the maximum amount of solute is dissolved in the solvent.
Supersaturated is a case in which more solute is dissolved in a solution than is normally
allowed. This can occur under special circumstances.
While the total amount of solute that is able to be dissolved in a solution remains constant at a
given temperature, the rate at which it can dissolve can be influenced by three methods: heating,
stirring, and grinding. Each of these will increase the rate at which a solute will dissolve. This
lab will show which of these factor increases the rate the most.
Molarity is a way of expressing how concentrated a solution is. This molarity is expressed in
moles of solute per liter of solution (solution being solute plus solvent). It is give the symbol, M.
Another way of expressing the amount of solute in solution is by the mass percent. This
percentage can be based on the mass of solute over the mass of solution, or the mass of solute
over the volume of solution (many biological applications use the latter).
In this experiment, the solubility of two solids in liquids will be investigated. The miscibility of
the various liquids will also be determined. The effects of heating, stirring, and grinding will be
determined using salt dissolving in water. Finally, the mass percent and concentration of salt in a
salt water solution will be determined using a forced evaporation method.
Experiment 12 – Solutions, Solubility, and Mass Percent
Name __________________
Lab Section __________________
Examples
1) A 25.0 mL solution sugar water (glucose, C6H12O6, in water) weighs 27.052 g. After the
water is evaporated, the solid glucose weighs 1.351 g. What is the mass percent of glucose in
the solution? What is the molarity of this solution?
To determine the % glucose, divide the mass of the glucose by the mass of the solution:
1.351 𝑔 𝑔𝑙𝑢𝑐𝑜𝑠𝑒
27.052 𝑔 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
𝑥 100% = 𝟒. 𝟗𝟗% 𝒈𝒍𝒖𝒄𝒐𝒔𝒆
To determine the molarity, first find the number of moles of the solute, then divide by the
volume of the solution in liters.
1.351 𝑔 𝑠𝑙𝑢𝑐𝑜𝑠𝑒 [
1 𝑚𝑜𝑙 𝑔𝑙𝑢𝑐𝑜𝑠𝑒
180.18 𝑔 𝑔𝑙𝑢𝑐𝑜𝑠𝑒
][
1
0.0250 𝐿
] = 𝟎. 𝟑𝟎𝟎 𝑴 𝒈𝒍𝒖𝒄𝒐𝒔𝒆
Experiment 12 – Solutions, Solubility, and Mass Percent
Name __________________
Lab Section __________________
Procedure
Solubility – Solids in Liquids
Set up six test tubes in your test tube rack. Place a small amount of potassium permanganate,
KMnO4, into the first three, and a small amount of iodine, I2, into the remaining three. Add
20 drops of water to the first test tube, 20 drops of hexane, C6H14, to the second test tube, and
20 drops of ethanol, CH3CH2OH, to the third. Gently shake each test tube and note whether
or not the solid dissolves in the liquid. Repeat this procedure for the test tubes containing I2.
Report whether the solids are soluble or insoluble in the liquids.
Miscibility – Liquids in Liquids
Set up three test tubes in your test tube rack. Put 20 drops of water into each of them. Add
20 drops of acetone, C3H6O, to the first test tube, 20 drops of hexane, C6H14, to the second
test tube, and 20 drops of ethanol, CH3CH2OH, to the third test tube. Shake gently and note
whether the liquids are miscible or immiscible.
Rate of Dissolving – Heat, Stir, Grind
Fill a small test tube half full of water. Put a small crystal of rock salt into this test tube and
set aside. Check back on the crystal periodically to note how long it will take for the crystal
to fully dissolve. This will be the rate of dissolving at room temperature (~21°C).
Half fill three small test tubes with deionized water and place them in a 250 mL beaker that is
half filled with water. See figure 19.1. Heat the beaker, with the test tubes in it, to boiling
and then turn off the burner.
Carefully add a crystal of rock salt to the first small test tube and note how long it takes for
the crystal to completely dissolve. This will be the rate of dissolving when the solute is
heated (~100°C).
Carefully add a crystal of rock salt to the second test tube and stir it with a glass stir rod and
note how long it takes the crystal to completely dissolve. This will be the rate of dissolving
when the solute is stirred.
To the last test tube, add a small amount of powdered salt and stir it with the glass stir rod.
Note how long it takes for the crystal to completely dissolve. This will be the rate of
dissolving when the solute is ground.
Note: Make sure that the amounts of salt are roughly the same. Also note that the
amount of time is qualitative, meaning that super precise timing is not necessary.
Experiment 12 – Solutions, Solubility, and Mass Percent
Name __________________
Lab Section __________________
Mass Percent and Molarity of Sodium Chloride in a Saltwater Solution
Obtain approximately 30 mL of and unknown salt solution in a clean, dry, small beaker, and
record its number.
Weigh a clean, dry evaporating dish.
Condition a graduated pipet with the salt solution. Put 10.0 mL of the salt water solution into
the evaporating dish and reweigh it.
Fill an appropriately sized beaker approximately ¾ full of water and support it on a ring
stand with an iron ring and wire gauze.
Place the evaporating dish on the beaker and heat the beaker to boiling using a Bunsen
burner, as shown in Figure 19.2. This will forcibly evaporate the water without boiling the
solution (which would send bits of solute flying out of the container).
Completely dry the saltwater solution until only dry salt remains in the evaporating dish.
Carefully remove the evaporating dish from the beaker and let it cool to room temperature.
Dry the bottom of the evaporating dish with a paper towel and weigh it.
Calculate the %NaCl and the molarity of the saltwater solution.
Repeat this procedure for reproducibility.
Experiment 12 – Solutions, Solubility, and Mass Percent
Name __________________
Lab Section __________________
Prelaboratory Questions
1) What is meant by the following terms?
Soluble
Miscible
Undersaturated, saturated, and supersaturated
Conditioning
Mass percent
Molarity
“like dissolves like”
2) A 10.0 mL sample of a potassium chloride solution is evaporated to leave only the solute in
the evaporating dish. If the following data were collected, what is the mass %KCl, and the
molarity of the solution?
Mass of evaporating dish and solution
Mass of evaporating dish
Mass of evaporating dish and KCl
76.241 g
60.758 g
61.454 g
Experiment 12 – Solutions, Solubility, and Mass Percent
Name __________________
Lab Section __________________
Data Table
Solubility – Solids in Liquids
Solvent
Solute
Water, H2O
Hexane, C6H14
Ethanol,
CH3CH2OH
KMnO4
I2
Miscibility – Liquids in Liquids
2nd Liquid
1st
Liquid
Acetone, C3H6O
Hexane, C6H14
Ethanol,
CH3CH2OH
H2O
Rate of Dissolving – Heat, Stir, Grind
Temperature
21°C
100°C
100°C
100°C
Stir Solute
Grind Solute
Time to Dissolve
Experiment 12 – Solutions, Solubility, and Mass Percent
Name __________________
Lab Section __________________
Mass Percent and Molarity of Sodium Chloride in a Saltwater Solution
Trial 1
Trial 2
Volume of saltwater solution
__________
__________
Mass of evaporating dish and saltwater solution
__________
__________
Mass of evaporating dish
__________
__________
Mass of saltwater solution
__________
__________
Mass of evaporating dish and NaCl
__________
__________
Mass of NaCl
__________
__________
Calculate the %NaCl of the solution – show calculations
%NaCl
__________
__________
Calculate the molarity of the saltwater solution – show calculations
Molarity of NaCl
__________
Average Molarity of NaCl
___________
__________
Experiment 12 – Solutions, Solubility, and Mass Percent
Name __________________
Lab Section __________________
Postlaboratory Questions
1) Indicate whether each of these solute/solvent pairs is soluble or insoluble:
Solvent
Solute
Water
Hexane
Ionic Solid
Polar Solid
Nonpolar Solid
Sugar
Wax
KCl
2) Indicate which of the liquid pairs is miscible or immiscible:
1st Liquid
2nd Liquid
Water
Alcohol
Hexane
Alcohol
Water
Oil
Oil
Gasoline
Miscible/Immiscible
3) What are the three ways to increase the rate of dissolving?
Which appears to affect the rate the most?
Experiment 12 – Solutions, Solubility, and Mass Percent
Name __________________
Lab Section __________________
4) A standard saline solution used for intravenous drips in hospitals is 0.90% weight per volume
𝑚𝑔
(instead of mass), or 9.000 𝐿 . What is the molarity of this solution?
𝑔
If the density of this solution is 0.997755 𝑐𝑚3 at 25°C, what is the %NaCl by mass?