II III I Solubility, Concentrations, & Molarity April
26-May 7, 2010
Slide 2
Solutions Definitions Solution -Solution - homogeneous mixture
consisting of two parts SolventSolvent - the substance that is
dissolving the solute ( present in greater amount ) SoluteSolute -
substance being dissolved
Slide 3
Measuring Concentration Concentrationa measure of
solute-to-solvent ratio Common Units: Molarity moles solute / L of
solution ppm g solute / 1,000,000 g of solution % g solute/ 100 g
of solution concentrated vs. dilute lots of solute not much solute
watery Add water to dilute a solution; boil water off to
concentrate it.
Slide 4
Measuring Concentration The amount of solute in a solution mol
L M A. mass % = mass of solute mass of solution B. parts per
million (ppm) also, ppb and ppt commonly used for minerals or
contaminants in water supplies C. molarity (M) = moles of solute L
of solution used most often in this class M = mol L % by mass
medicated creams % by volume rubbing alcohol
Slide 5
Mass Percent Parts of solute in every 100 parts solution. If a
solution is 0.9% by mass, then there are 0.9 grams of solute in
every 100 grams of solution. Or 10 kg solute in every 100 kg
solution. Since masses are additive, the mass of the solution is
the sum of the masses of solute and solvent. Tro's Introductory
Chemistry, Chapter 135
Slide 6
Molarity liter of solution
Slide 7
QUICK REVIEW OF MOLES!! The concentration can then be used to
convert the moles of solute into the liters of solution, or visa
versa. Since we normally measure the amount of solute in grams, we
will need to convert between grams and moles. How many moles are in
258 g of K 2 S?
Slide 8
Solution Concentration Molarity If a sugar solution
concentration is 2.0 M, 1 liter of solution contains 2.0 moles of
sugar, 2 liters = 4.0 moles sugar, 0.5 liters = 1.0 mole sugar: 8
Molarity = moles of solute liters of solution
Slide 9
Example 13.4How Many Liters of a 0.114 M NaOH Solution Contains
1.24 mol of NaOH? Tro's Introductory Chemistry, Chapter 13 9 The
unit is correct, the magnitude seems reasonable as the moles of
NaOH > 10x the amount in 1 L. Check: Solve: 1.00 L solution =
0.114 mol NaOH Solution Map: Relationships: 1.24 mol NaOH volume, L
Given: Find: mol NaOHL solution
Slide 10
Molarity Find the molarity of a solution containing 75 g of
MgCl 2 in 250 ml of water. 75 g MgCl 2 1 mol MgCl 2 95.21 g MgCl 2
= 3.2 M MgCl 2 0.25 L water
Slide 11
Calculating Molarity What is the molarity of a potassium
chloride solution that has a volume of 400 ml and contains 85.0
grams of KCl?
Slide 12
Example 2 Vinegar contains 5.0 grams of acetic acid,CH 3 COOH,
in 100.0 ml of solution. Calculate the molarity of acetic acid in
vinegar.
Slide 13
PracticeDetermine the Mass of CaCl 2 (MM = 110.98) in 1.75 L of
1.50 M Solution, Continued. Given:1.75 L solution Find:g CaCl 2
Equivalence:1.50 mol CaCl 2 1 L solution; 110.98 g = 1 mol CaCl 2
Solution Map: Tro's Introductory Chemistry, Chapter 13 13 L
solution mol CaCl 2 Apply Solution Map: Check Answer: Units are
correct. g CaCl 2
Slide 14
g solute / g of solution x 1,000,000= EXAMPLE There are 2.2 mg
of lead in exactly 500g of water. Convert this to ppm. Parts Per
Million (ppm)
Slide 15
Assignment Page 45 #1, #2, #3, #4, #5, #6, #8
Slide 16
Answers to Page 45 2. 3.
Slide 17
Answers to assignment Page 45 4. 5. 8.
Slide 18
Solubility When one substance (solute) dissolves in another
(solvent) it is said to be soluble. Salt is soluble in water. When
one substance does not dissolve in another it is said to be
insoluble. Oil is insoluble in water. There is usually a limit to
the solubility of one substance in another. Gases are always
soluble in each other. Two liquids that are mutually soluble are
said to be miscible. Alcohol and water are miscible. Oil and water
are immiscible. The maximum amount of solute that can be dissolved
in a given amount of solvent is called solubility. 18
Slide 19
Descriptions of Solubility Saturated solutions have the maximum
amount of solute that will dissolve in that solvent at that
temperature. Unsaturated solutions can dissolve more solute.
Supersaturated solutions are holding more solute than they should
be able to at that temperature. Unstable. Tro's Introductory
Chemistry, Chapter 1319
Slide 20
Solubility: forming a saturated solution in equilibrium
SATURATED SOLUTION no more solute dissolves UNSATURATED SOLUTION
more solute dissolves SUPERSATURATED SOLUTION becomes unstable,
crystals form increasing concentration
Slide 21
Changing Temperature = Changing Solubility When a solution is
saturated, it is holding the maximum amount of solute it can at
that temperature. The solubility of the solute in the solvent
depends on the temperature. If the temperature is changed, the
solubility of the solute changes. Higher temperature = Higher
solubility of solid in liquid. Lower temperature = Higher
solubility of gas in liquid. Tro's Introductory Chemistry, Chapter
1321
Slide 22
Saturation Problems!! Page 44 (#1) NaCl has a solubility of
35.9 g/100ml of water. Determine whether the following soln are
sat., unsat., supersat. 85 g of NaCl dissolved in 150 mL of water
25 g of NaCl dissolved in 750 g of water 135 g of NaCl dissolved in
750 g of water
Slide 23
Saturated, Unsaturated & Super Saturated Problems Problems
on Page 47 Do one for example Assign other two
Tasks: Thursday 4-23 Complete Lab write-up from the
Concentration Lab and 7 th Chromatography Lab also Page 46 #14,
#15, #16, #18 10. 3.7 grams 11. 33.6 grams 16. 3.51 grams 18. 4.03
mol/ liter
Slide 27
Page 44 2. a. Unsaturated (0.789) b. Unsaturated (0.975) c.
Unsaturated (0.66) 3. a. Supersaturated (5.1 x10 -4 ) b.
Supersaturated (0.029) c. Supersaturated (7.08 x 10 -5 ) Page 43
13.189 grams 14.0.18 L 15.0.082L
Slide 28
II III I Physical Properties & Characteristics of Solutions
April 24
Slide 29
Physical Properties of Solutions Conductivity: Ability to
conduct an electric current Depends on whether it contains charged
particles Do all compounds conduct electricity?
Slide 30
Electrolytes Timberlake, Chemistry 7 th Edition, page 290
Electrolytes Electrolytes - solutions that carry an electric
current NaCl(aq) Na + + Cl - HF(aq) H + + F - strong
electrolyteweak electrolytenonelectrolyte
Slide 31
Electrolytes Electrolytes are substances whose aqueous solution
(dissolved ions) is a conductor of electricity. Not all
electrolytes conduct same amount of electricity. In strong
electrolytes, all the electrolyte molecules are dissociated into
ions. In nonelectrolytes, none of the molecules are dissociated
into ions. No electric current. In weak electrolytes, a small
percentage of the molecules are dissociated into ions. 31
Slide 32
Healthy Info electrolytes: solutes that dissociate in solution
-- conduct electric current because of free-moving ions e.g.,
acids, bases, most ionic compounds -- are crucial for many cellular
processes -- obtained in a healthy diet -- For sustained exercise
or a bout of the flu, sports drinks ensure adequate electrolytes.
nonelectrolytes: solutes that DO NOT dissociate -- DO NOT conduct
electric current (not enough ions) e.g., any type of sugar
Slide 33
Colligative Properties The properties of the solution are
different from the properties of the solvent. Any property of a
solution whose value depends only on the number of dissolved solute
particles is called a colligative property. It does not depend on
what the solute particle is. The freezing point, boiling point, and
osmotic pressure of a solution are colligative properties. Tro's
Introductory Chemistry, Chapter 1333
Slide 34
Ice Cream Lab Data Average measurements over the entire day: 6
Tbs. salt= -8*C 12 Tbs. salt = -10*C 18 Tbs. salt = -15*C The more
salt that was added the lower the freezing point became!
Slide 35
Surfactants Definition: A chemical agent capable of reducing
the surface tension of a liquid in which it is dissolved Occurs at
the boundary of immiscible solutions Types: Detergent- synthetic,
works in hard water Emulsion- solution of two immiscible substances
(a colloid in which both phases are liquids; "an oil-in-water)
Soap- used to surround a molecule making it miscible (ex: surrounds
oil-allows it to dissolve in water)
Why Do We Do That? We spread salt on icy roads and walkways to
melt the ice. We add antifreeze to car radiators to prevent the
water from boiling or freezing. Antifreeze is mainly ethylene
glycol. When we add solutes to water, it changes the freezing point
and boiling point of the water. Tro's Introductory Chemistry,
Chapter 13 37
Slide 38
O 2- H+H+ H+H+ H2OH2O ++ ++ Water Molecule Water is a POLAR
molecule
Slide 39
Polar water molecules hydrates Na+ and Cl- ions Timberlake,
Chemistry 7 th Edition, page 287 HH O Na + + - - + - + + - Cl - + -
+ hydrated ions
Slide 40
Dissolving of NaCl in Water NaCl(s) + H 2 O Na + (aq) + Cl -
(aq)
Slide 41
Will It Dissolve? Chemists rule of thumb: Like dissolves like A
chemical will dissolve in a solvent if it has a similar structure
to the solvent. When the solvent and solute structures are similar,
the solvent molecules will attract the solute particles at least as
well as the solute particles to each other. Tro's Introductory
Chemistry, Chapter 13 41
Slide 42
Oil and Water Dont Mix Oil is nonpolar Water is polar Like
dissolves like, nonpolar dissolves nonpolar, nonpolar does not
dissolve polar Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002,
page 470
Slide 43
Will It Dissolve in Water? Ions are attracted to polar
solvents. Many ionic compounds dissolve in water. Generally, if the
ions total charges < 4. Polar molecules are attracted to polar
solvents. Table sugar, ethyl alcohol, and glucose all dissolve well
in water. Have either multiple OH groups or little CH. Nonpolar
molecules are attracted to nonpolar solvents. -carotene (C 40 H 56
) is not water soluble; it dissolves in fatty (nonpolar) tissues.
Many molecules have both polar and nonpolar structures whether they
will dissolve in water depends on the kind, number, and location of
polar and nonpolar structural features in the molecule. 43