MR. SURRETTE
VAN NUYS HIGH SCHOOL
CHAPTER 10: CHEMICAL SOLUTIONS
CLASSNOTES
SOLUTIONS
Chemical solutions are homogeneous mixtures of solute and solvent. Solutes are substances that are
dissolved in solutions. Solvents are substances present in greater amounts that dissolve the solutes.
Solutions can exist in the gas, solid, and liquid phases.
SOLID SOLUTIONS
Solid solutions consist of solids dissolved in other solids. Examples of solid solutions include “white
gold” (silver dissolved in gold), brass, and bronze.
ALLOYS
Sometimes metals are melted, stirred together, and cooled back down to solids. These solid metal
mixtures are called alloys.
GAS SOLUTIONS
Gas solutions consist of various gases mixed together. Air is a typical example of a gas solution.
LIQUID SOLUTIONS
All liquid solutions contain liquid solvents, but may contain liquid, solid, or gas solutes. For example,
rubbing alcohol is a liquid-liquid solution, cola is a gas-liquid solution, and sea
water is a solid-gas-liquid solution.
AQUEOUS SOLUTIONS
Normally the word “solution” refers to aqueous solutions. Aqueous solutions consist of solutes
dissolved in water.
HOW SOLUTES DISSOLVE
Solutes dissolve into solvents by separating into ions or molecules. These ions or molecules from the
solvent are invisible to the naked eye. They result from random molecular collisions with the solvent.
NON-POLAR VERSUS POLAR SOLVENTS
Atoms can share electrons evenly or unevenly. Atoms that share electrons evenly form non-polar
molecules. Atoms that share electrons unevenly form polar molecules.
NON-POLAR VERSUS POLAR SOLVENTS
Solvents can contain non-polar or polar molecules. Hexane, ethyl alcohol, and toluene are non-polar
solvents. Water, acetone, and methanol are polar solvents.
LIKE DISSOLVES LIKE
In general, when it comes to solutions, “like dissolves like,” so polar solvents tend to dissolve polar
solutes and non-polar solvents tend to dissolve non-polar solutes.
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CHEMISTRY
MR. SURRETTE
VAN NUYS HIGH SCHOOL
SOLVATION
Solvation is the attraction and association of molecules of a solvent with molecules or ions of a solute.
In general, solvation is a competition between the forces that hold the solute together and the solvent.
SOLVATION
If the forces that hold the solute together are stronger, the solute will not dissolve. If the forces that hold
the solute together are weaker than the solvent, then the solute will dissolve.
SOLVATION EXAMPLE
Stirring a teaspoon of sodium chloride (table salt) into a glass of water is a typical example of solvation.
NaCl in Solvation Reaction
SOLVATION EXAMPLE
In this case, the forces that hold the sodium and chlorine ions together are weaker than the water solvent.
SOLVATION EXAMPLE
The NaCl completely dissolves as the hydrogen (+) ends of the water molecules surround all the
chlorine anions and the oxygen (-) ends of the water molecules surround all the sodium cations.
SOLVATION RATE
Temperature, pressure, and surface area all affect solvation. In general, the following three factors
increase the speed of solvation:
1. Raising the temperature
2. Increasing the pressure
3. Increasing the surface area (for example, using a mortar and pestle to grind solute into powder)
SOLUBILITY AND SATURATION
Solubility measures how many grams of solute can dissolve in a solvent. With a few exceptions (like
gas-liquid solutions), solubility increases with increasing temperature.
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CHEMISTRY
MR. SURRETTE
VAN NUYS HIGH SCHOOL
SOLUBILITY AND SATURATION
Saturation is the maximum amount of solute that can dissolve in stable solution. The amount of
saturation also tends to increase with increasing temperature.
GAS-LIQUID SOLUBILITY
Gas-liquid solutions are exceptions to the solubility and saturation temperature trends. As the
temperature of gas-liquid solutions increases, the dissolved gases within them form additional bubbles
that escape the surface of the solution.
GAS-LIQUID SOLUBILITY
This means that the solubility and saturation of gas-liquid solutions decreases with increasing
temperature.
UNSATURATED SOLUTIONS
As the name suggests, unsaturated solutions contain less than the maximum amount of solute. This
means more solute can be added to them.
SUPERSATURATED SOLUTIONS
Supersaturated solutions contain unstable amounts of solute. Supersaturated solutions often form after
rapid cooling. “Rock candy” is a good example. Rock candy is made by adding sugar to boiling water
and chilling the solution to room temperature.
SUPERSATURATED SOLUTIONS
Tapping the side of the rock candy container or adding more solute causes the excess sugar to solidify
and precipitate out of solution.
ELECTROLYTES
Ionic solids like sodium chloride form electrolytes when dissolved in liquids. Electrolytes are charged
particles (cations and anions) found in liquid solutions.
CONCENTRATED AND DILUTE SOLUTIONS
Solutions contain various amounts of solutes. Some solutions contain high percentages of solute and
others contain low percentages.
CONCENTRATED AND DILUTE SOLUTIONS
Concentrated solutions have a high solute percentage and dilute solutions have a small solute
percentage.
SOLVENT TO SOLUTE RATIO
The ratio of solvent to solute within a solution is not fixed. The ratio can easily vary because the
concentrations of both the solvents and the solutes can be changed.
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CHEMISTRY
MR. SURRETTE
VAN NUYS HIGH SCHOOL
SOLUTION CONCENTRATION
We will look at four ways to measure solution concentration:
(1) Relative mass
(2) Mole fraction
(3) Molarity
(4) Molality
RELATIVE MASS
One way to measure the concentration of solutions is to compare the relative weights (in grams) between
the solute and the solvent.
RELATIVE MASS
The ratio of solute to solution can be measured as a mass percentage:
% Mass = (grams solute / grams solution) x 100
DENSITY OF WATER
Because aqueous solutions are common, it is important to know the density of water. The density of
water is one gram per milliliter at 20 oC (typical laboratory conditions).
DENSITY OF WATER
This is sometimes written:
WATER) = 1g / mL
Example 1. Calculate the % mass of 11.3 grams sucrose (table sugar) dissolved in 412.1 mL water.
1A.
(1) 412.1 mL water = 412.1 g water
(2) mass of solvent = 412.1 g
(3) mass of solute = 11.3 g
(4) mass of solution = mass of solute + mass of solvent
(5) mass of solution = 11.3 g + 412.1 g
(6) mass of solution = 423.4 grams
(7) % mass = (mass solute / mass solution) x 100
(8) % mass = (11.3 g / 423.4 g) x 100
(9) % mass = 2.67%
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CHEMISTRY
MR. SURRETTE
VAN NUYS HIGH SCHOOL
Example 2. Soda is 11.5% sucrose. What volume of soda in mL contains 85.2 g sucrose? (Assume the
density of soda = (WATER).
2A.
(1) 11.5 % sucrose = (11.5 g sucrose / 100 mL) (convert percentages into grams per 100 mL)
(2) Volume =
(85.2 g sucrose)
------------------1
x
(100 mL soda)
-----------------(11.5 g sucrose)
(3) Volume = 740.9 mL
Example 3. Soda is 11.5% sucrose. How many grams of sucrose are found in 355 mL of soda?
3A.
(1) 11.5% sucrose = (11.5 g sucrose / 100 mL)
(2) Mass =
355 mL
----------1
x
(11.5 g sucrose)
-------------------(100 mL)
(3) Mass = 40.8 g
MOLE FRACTION
Another way to measure solution concentration is to divide the moles of each solute by the moles of the
entire solution:
Mol fraction = mol solute / mol solution
Example 4. An electrum ingot forms by melting 62 grams of gold into 800 grams of silver. What are
the percentages of solute and solvent based on mole fractions?
4A.
Moles of gold:
(1) 62 g
(1 mol)
----- x ----------- = 0.315 mol Au
1
(196.97 g)
Moles of silver:
(2) 800 g
-------- x
1
(1 mol)
------------ = 7.416 mol Ag
(107.87 g)
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CHEMISTRY
MR. SURRETTE
VAN NUYS HIGH SCHOOL
4A. (continued...)
Total moles:
(3) Total moles = Au moles + Ag moles
(4) Total moles = 0.315 mol + 7.416 mol
(5) Total moles = 7.731 mols
Mole fractions:
0.315 mol Au
(6) Au mole fraction = -----------------------7.731 mol solution
(7) Au mole fraction = 0.041 x 100%
(8) Au mole fraction = 4.1% (solute)
(9) Since the Au mole fraction is 4.1%, the Ag mole fraction = 95.9%.
CONCENTRATION
The concentration of a solution measures the amount of solute per unit solvent. Concentration is
usually measured in moles per liter.
MOLARITY
Molarity (M) measures how many moles of solute are dissolved per liter of solution:
M = (moles of solute / liter of solution)
Example 5. What is the molarity of a solution that contains 15.5 grams NaCl dissolved in 1.5 liters
water?
5A.
Convert grams NaCl to moles:
(1) Na = 22.99 amu
(2) Cl = 35.45 amu
(3) NaCl = 58.44 g / mol
(4)
NaCl =
15.5 g
(1 mol NaCl)
------- x --------------1
(58.44 g)
(5) NaCl = 0.265 mol
Compute molarity of solution:
(6) M =
(0.265 mol NaCl)
---------------------(1.5 L)
(7) M = 0.18
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CHEMISTRY
MR. SURRETTE
VAN NUYS HIGH SCHOOL
Example 6. How many liters of 0.114 M NaOH solution contain 1.24 moles NaOH?
6A.
(1)
(1.24 mol NaOH)
(1 liter)
V = ----------------------------- x -------------------1
(0.114 mol)
(2) Volume = 10.9 L
DILUTIONS
Chemical solutions are often bottled in high concentrations. These concentrated solutions often have to
be diluted.
MOLARITY DILUTIONS
Molarity (M) and volume (L) are used to determine dilution ratios:
MIVI = MFVF
MOLARITY DILUTIONS
(MI = molarity of initial solution
VI = volume of initial solution
MF = molarity of final solution
VF = volume of final solution)
Example 7. How much 6.0 M NaNO3 is needed to make 0.585 L of 1.2 M NaNO3 solution?
7A.
Given: MI = 6.0 M, MF = 1.2 M, VF = 0.585 L
Find: VI
(1) MIVI = MF VF
(2) VI = MFVF / MI
(3) VI = (1.2 M)(0.585 L) / (6.0 M)
(4) VI = 0.117 L
MOLALITY
The other common unit for liquid solutions is molality, the number of moles of solute in 1 kilogram of
solvent.
MOLALITY
Molality contrasts with molarity because it compares the amount of solute relative to the mass of the
solvent (not the volume of solution):
m = mol solute / kg solvent
MOLALITY
For example, a 2 molal solution of hydrogen fluoride, abbreviated 2 m (with a lowercase “m” for
distinction from molarity), contains 2 moles of HF (40.02 grams) dissolved in 1,000 grams of H2O.
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CHEMISTRY
MR. SURRETTE
VAN NUYS HIGH SCHOOL
Example 8. 80 grams of glucose (C6H12O6) is added to 750 g of water. What is the molality of glucose
in the solution?
8A.
Molecular weight of glucose:
(1) 6 x C = 6 x 12.01 amu = 72.06 grams
(2) 12 x H = 12 x 1.01 amu = 12.12 grams
(3) 6 x O = 6 x 16.00 amu = 96.00 grams
==========
C6H12O6 molecular weight = 180.18 grams
Moles of glucose:
(4) 80 g C6H12O6
1 mol
------------- = 0.444 mol C6H12O6
180.18 g
Molality of glucose:
0.444 mol C6H12O6
(5) Molality = -------------------------0.75 kg solvent
(6) m = 0.592
TEMPERATURE
Temperature markedly affects the solubility of most substances. For example, the solubility of almost
all salts increases as temperature rises.
TEMPERATURE VERSUS SOLUBILITY
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