Title: LEARNING
1(No Transcript)
2LEARNING OBJECTIVES/ASSESSMENT When you have comp
leted your study of this chapter, you should be ab
le to 1. Classify mixtures as solutions or nons
olutions based on their appearance. (Section 7.1
Exercise 7.4) 2. Demonstrate your understanding
of terms related to the solubility of solutes in s
olution. (Section 7.2 Exercises 7.6 and 7.12)
3. Predict in a general way the solubilities of
solutes in solvents on the basis of molecular pola
rity. (Section 7.3 Exercise 7.16) 4. Calculat
e solution concentrations in units of molarity, we
ight/weight percent, weight/volume percent, and v
olume/volume percent. (Section 7.4 Exercises 7.2
2 b, 7.30 c, 7.34 a, and 7.38 c) 5. Describe how
to prepare solutions of specific concentration us
ing pure solutes and solvent, or solutions of gre
ater concentration than the one desired. (Section
7.5 Exercises 7.46 and 7.48 b) 6. Do stoichiom
etric calculations based on solution concentration
s. (Section 7.6 Exercise 7.56) 7. Understand c
olligative solution properties of boiling point, f
reezing point, and osmotic pressure and how to
determine osmolarity (Section 7.7 Exercises 7.
64 a c and 7.74) 8. Describe the characteristi
cs of colloids. (Section 7.8 Exercise 7.82) 9.
Describe the process of dialysis, and compare it
to the process of osmosis. (Section 7.9 Exercise
7.84)
3Mixtures
- Solutions (sometimes called true solutions) are
homogeneous mixtures of two or more substances in
which the components are present as atoms,
molecules, or ions. - Particles in these solutions are
- too small to reflect light, are transparent
(always clear but can be colored). - in constant motion and not settled by the
influence of gravity. - Heterogeneous mixtures
- Particles in these solutions are
- Large aggregates, reflect light (and are turbid)
and do settle out due to gravity - Colloidal solutions
- Particles in these solutions are
- Large aggregates, reflect light (and are turbid)
but do not settle out due to gravity (homogeneous
mixture)
4The dissolving process
5SOLUTION TERMINOLOGY
- Solutions can be solids, liquids or gases but we
will deal primarily with liquid solutions. - Solutions are composed of a solvent (main
component) and one or more solutes (substance
that is dissolved in the solvent) - Solubility the degree to which a solute
dissolves (insoluble, slightly soluble, soluble,
very soluble) - Miscible/immiscible terms that describe whether
a liquid solute dissolves or not - Saturated, unsaturated, supersaturated
6SOLUBILITY
- The solubility of a solute is the maximum amount
of the solute that can be dissolved in a specific
amount of solvent under specific conditions of
temperature and pressure.
7EXAMPLES OF SOLUTE SOLUBILITES AT 0C
8EXAMPLES OF SOLUTE SOLUBILITES AT 0C (continued)
9EFFECT OF TEMPERATURE ON SOLUBILITY
10THE SOLUTION PROCESS
- The solution process involves interactions
between solvent molecules (often water) and the
particles of solute. - An example of the solution process for an ionic
solute in water
11THE SOLUTION PROCESS (continued)
- An example of the solution process for a polar
solute in water
12THE SOLUTION PROCESS (continued)
- A solute will not dissolve in a solvent if
- the forces between solute particles are too
strong to be overcome by interactions with
solvent particles. - the solvent particles are more strongly attracted
to each other than to solute particles. - A good rule of thumb for solubility is like
dissolves like. - Polar solvents dissolve polar or ionic solutes.
- Nonpolar solvents dissolve nonpolar or nonionic
solutes.
13INCREASING THE RATE OF DISSOLVING
- Crush or grind the solute.
- Small particles provide more surface area for
solvent attack and dissolve more rapidly than
larger particles. - Heat the solvent.
- Solvent molecules move faster and have more
frequent collisions with solute at higher
temperatures. - Stir or agitate the solution.
- Stirring removes locally saturated solution from
the vicinity of the solute and allows
unsaturated solvent to take its place.
14HEAT AND SOLUTION FORMATION
Solute solvent heat? solution
Solute solvent ? solution heat
15SOLUTION CONCENTRATIONS
- Solution concentrations express a quantitative
relationship about the amount of solute contained
in a specific amount of solution. - Concentration units discussed include molarity
and percentage.
16MOLARITY
- The molarity of a solution expresses the number
of moles of solute contained in one liter of
solution. - The mathematical calculation of the molarity of a
solution involves the use of the following
equation - In this equation, the number of moles of solute
in a sample of solution is divided by the volume
in liters of the same sample of solution.
17PERCENT CONCENTRATIONS
- Percent concentrations express the amount of
solute contained in 100 parts of solution. The
parts of solution may be expressed in different
units. - Three variations exist for concentrations.
W/W, W/V or V/V generally expressed in grams and
mL if not then at least the same units. - To make solutions of M, W/V and V/V, the amount
of solute is measured out and solvent added to
the volume needed. - To make solutions of W/W , the grams of solvent
and solute are added to determine the weight of
the solution.
18CONCENTRATON CALCULATIONS
- Example 1 A 250-mL sample of solution contains
0.134 moles of solute. Calculate the molarity of
the solution. - 9.45 g of methyl alcohol, CH3OH, was dissolved in
enough pure water to give 500 mL of solution.
What was the molarity of the solution? - Calculate the (w/w) of a solution prepared by
dissolving 15.0 grams of table sugar in 100 mL of
water. The density of the water is 1.00 g/mL. - Calculate the (w/v) of a solution prepared by
dissolving 8.95 grams of sodium chloride in
enough water to give 50.0 mL of solution. - A solution is made by dissolving 250 mL of
glycerin in enough water to give 1.50 L of
solution. Calculate the (v/v) of the resulting
solution
19SOLUTION PREPARATION
- Solutions of known concentration are usually
prepared in one of two ways. - In one method, the necessary quantity of pure
solute is measured using a balance or volumetric
equipment. The solute is put into a container
and solvent, usually water, is added until the
desired volume of solution is obtained.
20SOLUTION PREPARATION EXAMPLE
- Calculation example Describe how to prepare 500
mL of 0.250 M NaCl solution. - Solution The mass of NaCl needed must first be
determined. The volume and concentration of the
desired solution are known, so the equation for
molarity is rearranged to solve for the number of
moles of solute needed. The result is - moles of solute M x liters of solution
0.250 M x
0.500 L 0.125 mole - Thus, 0.125 moles of NaCl is needed. NaCl has a
formula weight of 58.4 u, so 0.125 moles has a
mass of 0.125 x 58.4g or 7.30 grams. The
solution is prepared by weighing a sample of NaCl
with a mass of 7.30 grams. The sample is put
into a 500 mL volumetric flask and pure water is
added up to the mark on the flask.
21SOLUTION PREPARATION (continued)
- In a second method, a quantity of solution with a
concentration greater than the desired
concentration is diluted with an appropriate
amount of solvent to give a solution with a lower
concentration. This type of problem is made
simpler by using the following equation - (Cc)(Vc) (Cd)(Vd)
- In this equation, Cc is the concentration of the
concentrated solution that is to be diluted, Vc
is the volume of concentrated solution that is
needed, Cd is the concentration of the dilute
solution, and Vd is the volume of dilute solution.
22SOLUTION PREPARATION EXAMPLE
- Calculation example Describe how to prepare 250
mL of 0.500 M HCl solution from a 1.50 M HCl
solution. - Solution According to the definitions given
above, Cc 1.50 M, Cd 0.500 M, and Vd 250
mL. The equation given above can be solved for
Vc, the volume of concentrated solution needed - The solution is prepared by measuring 83.3 mL of
1.50 M HCl and pouring it into a 250 mL
volumetric flask. Pure water is then added up to
the mark on the flask to give 250 mL of 0.500 M
solution.
23SOLUTION STOICHIOMETRY
- As shown earlier, the number of moles of solute
in a volume of solution of known molarity can be
obtained by multiplying together the known
molarity and the solution volume in liters. - Molarity is a ratio of moles of solute to liters
of solution. This ratio can be written as two
conversion factors - The conversion factor on the left is used to
multiply by the molarity. It is selected to
cancel the units of liters of solution and obtain
the units of moles of solute. - The conversion factor on the right is used to
divide by the molarity. It is selected to cancel
the units of moles of solute and obtain the units
of liters of solution.
24SOLUTION STOICHIOMETRY EXAMPLE
- Calculation example Consider the balanced
equation - HCl(aq) NaOH(aq) NaCl(aq)
H2O(l) - How many mL of 0.100 M HCl solution would
exactly react with 25.00 mL of 0.125 M NaOH
solution?
25SOLUTION PROPERTIES
- Absolutely pure water conducts electricity very
poorly. - Some solutes called electrolytes produce water
solutions that conduct electricity well. - Some solutes called nonelectrolytes produce water
solutions that do not conduct electricity.
A solution of a strong electrolyte conducts
electricity well.
A solution of a weak electrolyte conducts
electricity poorly.
A solution of a nonelectrolyte does not conduct
electricity.
26ELECTROLYTES
- STRONG ELECTROLYTES
- Strong electrolytes form solutions that conduct
electricity because they dissociate completely
into charged ions when they dissolve. - WEAK ELECTROLYTES
- Weak electrolytes form weakly conducting
solutions because they dissociate into ions only
slightly when they dissolve. - NONELECTROLYTES
- Nonelectrolytes form nonconducting solutions
because they do not dissociate into ions at all
when they dissolve.
27COLLIGATIVE PROPERTIES OF SOLUTIONS
- Colligative solution properties are properties
that depend only on the concentration of solute
particles in the solution. Three colligative
properties are boiling point, freezing point, and
osmotic pressure. - Experiments demonstrate that the vapor pressure
of water (solvent) above a solution is lower than
the vapor pressure of pure water.
28SOLUTION BOILING POINT
- The boiling point of a solution is always higher
than the boiling point of the pure solvent of the
solution. - Since BP elevation is a colligative property,
dependent only on the concentration of particles,
the following substances would have an equal
impact on BP elevation (or any other colligative
property) - 0.1 M CaCl2
- 0.15 M NaCl
- 0.3 M sugar (non-electrolyte)
29SOLUTION BOILING POINT (continued)
- For example, the dissociation of calcium chloride
is represented as - CaCl2 Ca2 2 Cl-
- Thus, when 1 mole of CaCl2 dissolves, 3 moles of
particles (ions) are put into the solution.
30SOLUTION FREEZING POINT
- The freezing point of a solution is always lower
than the freezing point of the pure solvent of
the solution.
31OSMOTIC PRESSURE OF SOLUTIONS
- When solutions having different concentrations of
solute are separated by a semipermeable membrane,
solvent tends to flow through the membrane from
the less concentrated solution into the more
concentrated solution in a process called
osmosis. - When the more concentrated solution involved in
osmosis is put under sufficient pressure, the net
osmotic flow of solvent into the solution can be
stopped. - The pressure necessary to prevent the osmotic
flow of solvent into a solution is called the
osmotic pressure of the solution and can be
calculated by using the following equation, which
is similar to the ideal gas law given earlier - p nMRT
32OSMOTIC PRESSURE OF SOLUTIONS (continued)
- In this equation, p is the osmotic pressure, n is
the number of moles of solute particles put into
solution when 1 mole of solute dissolves, M is
the molarity of the solution, R is the universal
gas constant written as 62.4 L torr/K mol, and T
is the solution temperature in Kelvin. - The product of n and M is called the osmolarity
of the solution.
33COLLOIDS
- Colloids are homogeneous mixtures of two or more
components called the dispersing medium and the
dispersed phase. The dispersed phase substances
in a colloid are in the form of particles larger
than those found in solutions. - DISPERSING MEDIUM OF A COLLOID
- The dispersing medium of a colloid is the
substance present in the largest amount. It is
analogous to the solvent of a solution. - DISPERSED PHASE OF A COLLOID
- The dispersed phase of a colloid is the substance
present in a smaller amount than the dispersing
medium. It is analogous to the solute of a
solution.
34COLLOID PROPERTIES
- In colloids, the dispersed phase particles cannot
be seen and do not settle under the influence of
gravity. - Colloids appear to be cloudy because the larger
particles in the dispersed phase scatter light. - Colloids demonstrate the Tyndall effect in which
the path of the light through a colloid is
visible because the light is scattered.
35TYPES OF COLLOIDS
36STABILIZING COLLOIDS
- Substances known as emulsifying agents or
stabilizing agents are used to prevent some
colloids from coalescing (e.g. egg yolk in oil
and water to form mayonnaise, soap/ detergent
ions forming a charged layer around nonpolar oils
and greases).
37STABILIZING COLLOIDS (continued)
38DIALYSIS
- Dialysis can be used to separate small particles
from colloids (e.g. cleaning the blood of people
suffering from kidney malfunction).
39DIALYSIS
- A dialyzing membrane is a semipermeable membrane
with larger pores than osmotic membranes that
allow solvent molecules, other small molecules,
and hydrated ions to pass through. - Dialysis is a process in which solvent molecules,
other small molecules, and hydrated ions pass
from a solution through a membrane.