XII – Solutions and Concentration
Chemistry Student Notes
Chemistry Unit XII – Solutions and Concentration
PRE-TEST QUESTIONS
1. What is the chemical formula of water?
2. What is the VSEPR geometry of a water molecule?
3. Is water a polar or a nonpolar molecule?
4. Is a solution of sugar water a homogenous or heterogeneous mixture?
5. Can you name anything that does not mix with water?
I. Water and Its Properties
A. Properties of water
1. Water exists in many forms in nature:
a. Oceans
b. Lakes
c. Ponds and rivers
d. Icebergs
e. Groundwater
f. Polar ice caps
g. Snow
2. Remember the properties of water
a. Water’s formula is H2O.
b. ________________ molecule with 2 hydrogen atoms sharing an electron pair with
the ________________ atom in the middle.
c. The two lone pairs of electrons on the oxygen atom cause the molecule to have a bent
shape, with a bond angle at ________________ (which is very narrow when
considering that other bond angles on other molecules are a bit wider).
d. Because oxygen is ________________ electronegative than the hydrogen atoms,
oxygen attracts the electrons to itself more, granting oxygen a partial
________________ charge and as a consequence, the hydrogen atoms have partial
________________ charges.
e. Because water is bent, and because of the difference in electronegativity between
oxygen and hydrogen, water is a ________________ molecule.
3. In general, polar molecules are attracted to one another by dipole interactions.
a. But because water has a hydrogen bonded to a very electronegative element (oxygen),
the dipoles are ‘upgraded’ (if you will) to ________________ bonds.
4. Many unique and important properties of water—including water’s ________________
surface tension and ________________ vapor pressure—result from hydrogen bonding.
B. Surface Tension
1. Water molecules are attracted to other ________________ molecules through
________________ bonds.
2. At water’s surface, water molecules are not surrounded by other water molecules, so they
bond more strongly to one another at the surface.
a. As a result, water tends to be drawn ________________.
3. Surface tension is an inward force that tends to ________________ the surface area of a
liquid; it cases the surface to behave as if it were a thin skin.
a. This is why water “________________ up.”
4. All liquids have surface tension, but water is extremely _____________ in comparison.
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UNIT XII Notes, Page 1
XII – Solutions and Concentration
Chemistry Student Notes
5. The addition of a surfactant can ________________ the surface tension.
a. A surfactant is any substance that interferes with the hydrogen bonding between
water molecules and thereby ________________ surface tension.
b. ________________ and ___________________ are commonly-used surfactants.
C. Vapor Pressure
1. Remember that vapor pressure is a result of molecules ________________ from the
surface of a liquid and entering the ________________ phase.
2. Because hydrogen bonds hold water molecules to one another, the tendency of these
molecules to escape the liquid phase is low.
a. Thus, evaporation is ________________.
b. And thus, water has a ________________ vapor pressure.
3. If water wasn’t like this, then all bodies of water would evaporate much more easily.
D. Water in the Solid State
1. Water’s density increases as it gets colder until 4°C, where its density is
___________________. Then, it decreases a little and when it freezes solid, it goes to
___________________.
2. When water freezes, the particles occupy ________________ space as a solid than they
do as a liquid.
a. Most liquids ________________ when they freeze, causing them to be
________________ dense in the solid state.
b. But water occupies _____________ space (volume) as a solid, so the density is lower.
c. This has the result of solid water (ice) ________________ on liquid water.
d. The structure of ice is a regular, open framework of water molecules arranged much
like a honeycomb.
3. This means that ice floats on top when it freezes in ponds during the winter. This actually
acts as an ______________________ layer and keeps fish, amphibians, and other life
from freezing during the winter.
4. It’s worth pointing out that ice melts at ________________, which is actually a pretty
________________ melting point for a molecule that has such a small molar mass.
a. It also takes a ________________ of heat energy to melt ice.
b. It takes ________________ Joules to melt 1 gram of water, and that same amount of
heat will raise the temperature of 1 gram of liquid water from 0°C to 80.°C.
II. Homogeneous Aqueous Systems
A. Solvents and Solutes
1. Water will dissolve lots of substances.
2. An aqueous solution is ________________ that contains dissolved substances.
3. In solutions,
a. The ________________ is the substance being dissolved.
b. The ________________ is the dissolving medium (what is doing the dissolving).
4. A solvent dissolves the solute. The solute becomes dispersed in the solvent.
5. Solvents and solutes can be ________________ state of matter.
6. A ________________ is another name for homogeneous mixtures that are stable. In salt
water, for instance, the ________________ stays dissolved.
a. A solution ___________________ be separated by filtration.
7. Substances that dissolve most readily in water include ionic compounds and polar
covalent molecules. Nonpolar covalent molecules do _____________ dissolve in water.
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UNIT XII Notes, Page 2
XII – Solutions and Concentration
Chemistry Student Notes
a. To understand all of these relationships, you need to understand the
________________ of the particles involved.
B. The Solution Process
1. Particles are in ________________ motion and when any solute is placed in water, the
particles of water ________________ with it.
2. As individual solute ions break away from the crystal, the negatively and positively
charged ions become surrounded by solvent molecules and the ionic crystal dissolves.
3. Solvation is a process that occurs when an ionic solute dissolves; in solution, solvent
molecules surround the positive and negative ions.
C. Dissociation
1. Dissociation is the separation of ________________ in an ionic compound as the
compound dissolves.
a. Occurs in ________________ compounds.
2. In order for a substance to dissolve, the solute and solvent must be __________________
to each another.
3. When salt, NaCl, dissolves in water, there is an _____________________ between the
polar molecule H2O and the Na+ and Cl¯ ions.
D. Dispersion of Molecular Compounds
1. Dispersion is the process of ___________________ by breaking into
________________ pieces.
a. This generally occurs in ________________ covalent compounds in water, or
________________ compounds in ________________ solvents.
2. A piece of hard candy on your tongue, the taste ________________ out, or disperses, in
your mouth.
a. Both sugar and water are ________________ molecules, so they ________________
one another.
b. ________________ form between the water molecules and the exposed sugar
molecules.
c. When enough water molecules have ________________ a sugar molecule, the
attractions between them are great enough to ________________ the attractions
holding the sugar molecule to the surface of the crystal.
d. The sugar molecule breaks ________________, and is pulled into solution by the
water molecules.
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UNIT XII Notes, Page 3
XII – Solutions and Concentration
Chemistry Student Notes
E. Ionization
1. Ionization is the process whereby neutral molecules gain or lose electrons and thus,
become ________________, or ________________.
a. Happens when ________________ covalent molecules become ________________.
2. Unlike dissociation and dispersion, which are ________________ changes, dissolving by
ionization is a ________________ change.
3. HCl, hydrochloric acid dissolves in water.
a. When it does so, the H+ ion (called a proton) from the acid becomes solvated by the
water molecules and forms a new substance, H3O+, called ________________.
F. Rules of Solubility
1. Many ionic compounds dissolve well in water.
2. Some ionic compounds, however, are more ________________ attracted to one another
and do not dissolve in water.
a. BaSO4 and CaCO3 are good examples of these.
3. Oil and water do not mix because oil is a nonpolar substance and water is a polar
molecule.
a. The general rule of dissolving is “___________ _________________ ___________.”
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XII – Solutions and Concentration
Chemistry Student Notes
b. This means that oil, a ________________ substance, will dissolve other nonpolar
substances, such as ________________, ________________, or ________________.
c. Water, a polar substance will dissolve other polar substances (or charged particles
like ionic compounds such as NaCl) such as sugar, etc.
4. Some compounds, like most alcohols have a nonpolar end (the carbon chain) and a polar
end (the alcohol –OH end).
a. These will dissolve both polar and nonpolar compounds, but will not dissolve ionic
compounds.
Common Polar Solvents
Common Nonpolar Solvents
G. Electrolytes and Nonelectrolytes
1. An electrolyte is a substance that ________________ an electric current when in
aqueous solution or in the molten state.
a. ________________ (polar molecular compounds) and _____________
_______________ are often good electrolytes.
2. In order to conduct electricity, the mixture must contain ________________ (or
________________ particles) that are ________________.
a. All acids are electrolytes because they form ________________ in solution.
b. All ionic compounds are electrolytes because they ________________ into ions.
c. ________________ is key!
3. A compound that does not conduct an electric current in either ________________
solution or the molten state is called a ____________________.
a. Most organic (contains ________________) compounds [sugars, alcohols, etc.] do
not conduct electricity.
4. Compounds that ionize in solution usually ________________ electricity.
a. NH3 and HCl are two good examples of this.
i. NH3 (g) + H2O (l) →
ii. HCl (g) + H2O (l) →
5. A strong electrolyte is a solution in which a ________________ portion of the solute
exists as ________________.
a. HCl is a ________________ acid. All ________________ acids ionize almost
________________, so it would be a strong electrolyte as well.
b. Ammonia, a ________________ base, ionizes, but only partially, so is not considered
a strong electrolyte.
c. All soluble ________________, ________________ inorganic acids and
________________ bases are strong electrolytes.
6. A weak electrolyte conducts electricity poorly because only a ________________ of the
solute in the solution exists as ions.
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UNIT XII Notes, Page 5
XII – Solutions and Concentration
Chemistry Student Notes
H. Hydrates
1. A compound that has a specific number of water molecules bound to each formula unit is
called a hydrate.
a. e.g., CuSO4•5H2O, Copper(II) sulfate pentahydrate
2. If a hydrate is heated, it will ________________ the water molecules, most likely change
appearance, to what is called the anhydrous form (free from water).
3. Hydrates and other compounds that remove moisture from air are called
________________.
a. Calcium chloride (ice melt) will do this.
b. A ________________ is a substance used to absorb moisture from the air and create a
dry atmosphere.
i. Like Silica gel packets often found packaged in electronics and shoes.
4. ________________ compounds can remove sufficient water from the air to dissolve
itself completely in water and form a solution.
III. Heterogeneous Aqueous Systems
A. Suspensions
1. A suspension is a mixture from which particles ________________ out upon standing,
2. Suspensions differ from solutions because the particles of a suspension are much
________________ and do not stay suspended indefinitely.
a. Particles in suspensions are generally ________________ (1000 nm in diameter
whereas a solution’s particles are about 1 nm in diameter).
3. Suspensions are heterogeneous because at least two substances can be clearly identified.
a. Unlike solutions, suspensions can be separated by ________________.
B. Colloids
1. A colloid is a heterogeneous mixture containing particles that range in size from 1 nm to
1000 nm, somewhere ________________ solutions and suspensions in size.
a. e.g.,
2. Like suspensions, many colloids are cloudy or milky in appearance when they are
concentrated, or they can appear clear.
3. The important difference between colloids, suspensions and solutions is the
________________ of the particles.
a. The intermediate-sized particles in a colloid ________________ be retained by filter
paper (instead, they pass through), and they do _____________ settle out with time.
4. Tyndall Effect
a. The ________________ of visible light by colloidal particles is called the Tyndall
effect.
b. Suspensions also exhibit the Tyndall effect, but solutions do ________________.
c. Like seeing a beam of sunlight through dust or mist.
5. Brownian Motion
a. Brownian Motion is the chaotic movement of colloidal particles, cause by collision
with particles of the solvent in which they are dispersed.
b. These collisions help ________________ the colloidal particles from settling.
6. Emulsions
a. An emulsion is a colloidal dispersion of a liquid in a liquid.
i. e.g., oil is not soluble in water, but will form a colloidal dispersion if soap or
detergent is added to the water.
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XII – Solutions and Concentration
Chemistry Student Notes
b. ________________ and ________________ are emulsifying agents.
c. Soaps and other emulsifying agents allow the formation of colloidal dispersions
between liquids that otherwise, would ____________ ordinarily ____________.
d. Examples: Mayonnaise (oil and vinegar), milk, margarine, butter, cosmetics,
shampoos and lotions.
Property
Solution
System
Colloid
Suspension
Particle Type
Particle Size
Effect of Light
Effect of Gravity
Filtration
Uniformity
IV. Properties of Solutions
A. Solutions
1. Solutions are homogeneous mixtures that may be solid, liquid or gaseous.
2. How can you increase the rate of dissolving?
a. ________________________________________________________________
b. ________________________________________________________________
c. ________________________________________________________________
B. ________________ and Solution Formation
1. Dissolving occurs at the ________________ of the solute.
2. Stirring increases the amount of fresh solvent coming into contact with the solute.
3. This only affects the rate of dissolving, not how much will dissolve (solubility).
C. ________________ and Solution Formation
1. At higher temperatures, the kinetic energy of water molecules is greater, so they move
________________.
2. This more rapid movement of the solvent molecules leads to an increase in the frequency
and force of the collisions between water molecules and the surface of the sugar crystals.
D. ________________ ________________ and Solution Formation
1. The smaller the pieces of a sample are, the ________________ surface area they have
and thus, the more they can interact with the solvent and thus, dissolve.
2. Draw…
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UNIT XII Notes, Page 7
XII – Solutions and Concentration
Chemistry Student Notes
E. Solubility
1. The solubility of a substance is the amount of solute that dissolves in a given quantity of
a solvent at a specified temperature and pressure to produce a saturated solution.
a. Note this is not how ________________ it dissolves.
2. A saturated solution contains the ________________ amount of solute for a given
quantity of solvent at a constant temperature and pressure.
a. Any additional solute added will ________________ dissolve.
3. An unsaturated solution is a solution that contains less solute than a saturated solution
at a given temperature and pressure.
a. Any additional solute will
dissolve until the saturation
point is reached.
4. Solubility is a dynamic
equilibrium process!
a. If more solute is added
above the saturation point,
it will not dissolve, no
matter how much it is
crushed up or stirred.
i. In fact, solid sitting on
the bottom of the flask
indicates the solution is
________________.
b. An ________________
process occurs.
c. Particles from the solid get
solvated and enter into
solution (they are
________________).
d. At the same time, an equal
number of already
dissolved particles
________________ and
reenter the solid phase.
e. The mass of undissolved
crystals, however, remains ________________.
5. Solubility is generally expressed in grams of solute per 100 grams of solvent.
a. Gases, occupying more space, may be expressed in grams per liter (g/L).
F. Miscibility
1. Some liquids like ethanol and water dissolve in one another in __________ proportions.
2. They are said to be ________________.
3. Liquids that do not mix, then, are called ___________________.
G. Factors Affecting Solubility
1. Temperature
a. For most solid substances, their solubility ________________ as the temperature of
the solvent increases.
b. This property is used to make supersaturated solutions. See below.
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XII – Solutions and Concentration
Chemistry Student Notes
2. Temperature and Gases
a. The solubility of most gases is ________________ in cold water than in hot water.
b. This occurs because gas particles slow down and stay in solution better in colder
water.
c. Note the dotted lines in the solubility curve graph.
3. Pressure
a. Changes in pressure affect only ________________.
b. Henry’s Law states that at a given temperature, the solubility of a gas in a liquid is
directly proportional to the pressure of the gas above the liquid.
i. In other words, as the pressure of the gas above the liquid increases, the solubility
of the gas ________________.
H. Making Supersaturated Solutions
1. A supersaturated solution contains more solute than it can theoretically hold at a given
temperature.
2. To make a supersaturated solution…
a. Make a ________________ solution at a given temperature.
b. ________________ up the solution.
c. Add solute to make the solution saturated at this new, ______________ temperature.
d. Carefully ________________ the solution.
3. Supersaturated solutions are very unstable and excess solute will precipitate if a seed
crystal is added.
V. Concentration
A. Concentration
1. Saying something is “concentrated” is very vague.
2. The concentration of a solution is a measure of the amount of solute that is dissolved in
a given quantity of solvent.
3. A dilute solution is one that contains a ________________ amount of solute.
4. A concentrated solution contains a ________________ amount of solute.
B. Percent
1. This can be done either by mass or by volume.
2. The formulas for these would be:
EXAMPLE XII-01: Percent By Mass
1. A solution of sodium chloride is prepared by dissolving 5.0 g of salt in 550 g of water.
What is the concentration of this solution, as given by percent mass?
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UNIT XII Notes, Page 9
XII – Solutions and Concentration
Chemistry Student Notes
EXAMPLE XII-02: Percent By Volume
1. How much isopropyl alcohol is in 2.0 L of a 70.% by volume solution?
C. Molarity
1. Molarity is the most common means of measuring concentration in chemistry.
2. Molarity (M) is the number of moles of solute dissolved in one liter of solution.
3. So, a “one molar” solution of sodium hydroxide means that one mole of NaOH has been
dissolved for every liter of solution (NaOH + water).
4. The formula for molarity is
EXAMPLE XII-03: Molarity
1. What is the molarity of 3.50 L of solution that contain 90.0 g of sodium chloride?
D. Molality
1. Molality (m) is the number of moles of solute dissolver per kilogram of solvent.
2. So, a “one molal” solution of ammonia means that one mole of ammonia is dissolved per
kilogram of solvent (water).
3. The formula for molality is
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UNIT XII Notes, Page 10
XII – Solutions and Concentration
Chemistry Student Notes
EXAMPLE XII-04: Molality
1. A solution contains 17.1 g of sucrose (C12H22O11) dissolved in 125 g of water. Find the
molal concentration of this solution.
E. Dilutions
1. Diluting a solution by adding more solvent reduces the number of moles per unit volume,
but the total number of moles solute in solution does not change.
a. Moles of solute before dilution = moles of solute after dilution
2. To dilute a solution, we use the following equation:
EXAMPLE XII-05: Dilution
1. What volume of a 2.0 M HCl solution should be used to create 500. mL of a 0.50 M
HCl solution?
VI. Colligative Properties
A. Colligative Properties: An Introduction
1. A colligative property is a property of a solution that depends only upon the
________________ of nonvolatile solute particles in the solution.
a. They depend only on the ________________ of particles, regardless of what those
particles may be.
2. The easiest way to remember most colligative properties is that the attraction between the
particles and the liquid solvent means that the solvent wants to stay in the
________________ phase.
3. Ionic solutes that dissociate, such as sodium chloride and calcium chloride, have greater
effects on the vapor pressure than does a nondissociating solute, such as glucose.
a. Glucose will form ________ ________ unit in solution:
b. NaCl will form ________________ ions:
c. CaCl2 will form ________________ ions:
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XII – Solutions and Concentration
Chemistry Student Notes
4. Thus, CaCl2 is ________________ effective than NaCl, which is ________________
effective than glucose at affecting colligative properties.
B. Vapor-Pressure Lowering
1. A solution that contains a solute that is nonvolatile (not easily vaporized) always has a
________________ vapor pressure than the pure solvent.
2. When a solute is dissolved in water, within the liquid and at the surface, the ions are
surrounded by layers of associated water molecules, or shells of water of salvation.
3. These ________________ the number of particles that have enough kinetic energy to
escape the liquid state.
a. Thus, more particles stay ________________ and do not vaporize.
4. The decrease in a solution’s vapor pressure is proportional to the number of particles the
solute makes in solution.
C. Freezing-Point Depression
1. The presence of a solute in water disrupts the formation of the orderly pattern of a solid
crystallizing because of the shells of water of salvation.
2. As a result, more kinetic energy must be withdrawn from a solution to cause it to solidify
(as opposed to pure solvent which would require less).
3. The freezing point of a solution is ________________ than the freezing point of the pure
solvent.
4. The difference in temperature between the freezing point of a solution and the freezing
point of the pure solvent is the freezing-point depression.
5. The magnitude of the freezing-point depression is proportional to the number of solute
particles dissolved in the solvent and does not depend upon their identity.
6. The addition of 1 mole of solute particles to 1000 g of water lowers the freezing point by
________________.
a. Without a solute, pure water has a freezing point of ________________.
b. Add 1 mole glucose to water, it lowers the freezing point to ________________.
c. Add 1 mole NaCl to water, it lowers the freezing point to ________________.
d. Add 1 mole CaCl2 to water, it lowers the freezing point to ________________.
7. This is how antifreeze (ethylene glycol (C2H6O2)) works.
D. Boiling-Point Elevation
1. Just like how dissolved particles lower the freezing point, they also ________________
the boiling point.
2. The difference in temperature between the boiling point of a solution and the boiling
point of the pure solvent is called the boiling-point elevation.
a. Antifreeze, added to automobile engines to prevent freeze-ups in water, also protect
the engine from ________________ ________________ in summer.
3. The magnitude of the boiling-point elevation is proportional to the number of solute
particles dissolved in the solvent.
4. The boiling point of water increases by ________________ for every mole of particles
that the solute forms when dissolved in 1000 g of water.
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UNIT XII Notes, Page 12