Transcript Solutions - My Teacher Pages

Solutions
CPS Chemistry
Definitions
 Solutions
 A homogeneous mixture of two or more
substances in a single phase
 Soluble
 Capable of being dissolved
 Solvent
 Dissolving medium in a solution
 What is doing the dissolving
 Solute
 Substance dissolved in a solution
 What is dissolved
 Example
 Sugar in tea –
 tea is solvent, sugar solute
Types of Solutions
 May exist as gasses, liquids or solids
 One component is designated as
solvent and one as solute
 Chart on pg. 396
Phase
 If there are two different types of
substances it is a phase change
 Water + salt; water and gas
 Same phase
 Water and apple juice
 This is an aqueous solution
 Means there is water involved
 Alcohol and liquid
 Tincture solution
 Means there is alcohol involved
Mixtures
 2 or more substances when each
retains its properties
 Homogeneous





Uniform distribution of particles
0.01-1nm size particles, can be atoms
Can be physically separated
Ex. Salt water, air
Also called solution
 Heterogeneous
 Distribution of particles is not uniform
 Can be separated by physical means
 Particle size 1-1000 nm (nanometer)
Suspensions
 When particles in a solvent are so
large that they settle out unless
stirred constantly
 Gravity pulls particles to bottom of
container
 Particles >1000nm in diameter, 1000
times as large as atoms
 Ex. Italian salad dressing, muddy
water
 Can be separated by passing liquid
through a filter
Colloids
 Has particles that are intermediate in
size and they remain dispersed in the
solute
 1-1000nm particle size
 Emulsion or foam are specific types
 Mayonnaise is an emulsion of egg and
oil
The Tyndall effect
 Is a sign that it may be a colloid
 The particles are not large enough to
be seen, but large enough to scatter
light
 Ex: headlights on a foggy night
Test tube
Light Beam
Tyndall Effect, beam of light can be seen in
suspensions and colloids
Test tube
Light Beam
No Tyndall Effect, beam of light cannot be
seen in solutions
Electrolytes vs. Nonelectrolytes
 Electrolyte
 A substance that dissolves in water to
give a solution the ability to conduct
electricity
 Nonelectrolyte
 A substance that when dissolved in water
to make a solution that does not conduct
electricity
 When ionic compounds dissolve, the
positive and negative ions separate
from each other and are surrounded
by water molecules
 When the ions are free to move,
electricity moves easily
How to Make Solutions
 You need to know the:
 Solubility –the maximum amount solute
can dissolve in a solvent
 Rate – how fast the solute dissolves
Factors that affect rate of
dissolution
 Surface area of the solute
 The larger the surface area, the more
quickly it dissolves
 Agitation of a solution
 When you stir or shake the solute
particles are dispersed throughout the
solvent, and it increase the rate of
dissolution
Saturated Solutions
 A solution that contains the maximum
amount of dissolved solute is
saturated
 The factors that determine saturation
are mass of solvent, mass of solute
and the temperature
 When a solution contains less than
the maximum saturation it is
considered unsaturated
Supersaturate
 A solution that contains more
dissolved solute than a saturated
solution contains under the same
conditions
 But will form crystals when disturbed
or cooled
Like dissolves like
 The rule for predicting whether one
substance will dissolve in another is
related to the type of bonding, the
polarity of a molecule and the
intermolecular forces between the
solute and solvent
 Things need to be similar for them to
dissolve
Solvent
Solute
= Solution
Polar
Polar
Nonpolar
Nonpolar
Polar
non-polar
Polar
Nonpolar
=
=
=
=
yes
no
no
yes
Reminder molecule polarity
More Vocab.
 Immiscible
 Liquid solutes and solvents that are not
soluble in each other
 Oil and water
 Oil and salt
 Miscible
 Liquids that dissolve freely in one
another in any proportion
 Water and food coloring
Back to Temperature- Solubility
 Increase temp =increase KE=
increase in solubility + increase in
rate
 Higher temps dissolve faster( Liquids)
BUT
 Gasses act differently
 Increase temp = decrease solubility
 Because gasses will leave solution at high
temps
Pressure –solubility
 There is no difference to solids or
liquids, but with an increase in
pressure it will increase the solubility
of a gas
 For example CO2 dissolved in a solution
of sucrose and water (soda) will come
out of solution when the pressure is
decreased (opening the bottle, lets the
soda bubble)
Size of the Particle – rate
 Because the dissolution occurs only at
the surface of the solute, when you
crush a substance,
 You get a larger surface, so you
increase the rate at which it is
dissolved
Stirring - rate
 When you agitate the solvent, you
increase the contact with the surface
of the solute
 You increase the rate
Amount of Solute -rate
 As you increase the amount of solute
you want to dissolve
 You decrease the solubility and rate
Concentration
 A measure of the amount of solute in
a given amount of solvent or
soulution
 MATH IS INVOLVED
Molarity
 The number of moles of solute in one
liter of solution
 Molar mass- as a reminder it is the
mass listed on the PTE.. If it is for a
compound, you simly add the masses
of the atoms of the emperical formula
 Ex. H2O H=1.00 O=15.99 total
molar mass is 1.00+1.00+15.99
=17.99g
Formula
Molarity ( M) =
Amount of solute (mol)
______________________
Volume of solution (L)
Practice
 You have3.50 L of solution that
contains 90.0 g of sodium chloride,
NaCl. What is the molarity of that
soulution?
 Mass of solute 90.0
 Solution volume = 3.50 L
 Molar Mass if NaCl 58.44 g/mol
Molality
 Don’t confuse them…
 The concentration of a solution
expressed in moles of solute per
kilogram of solvent
 You measure the mass of the
solvent…
Formula
Molality =
moles of solute (mol)
______________________
mass of solvent (Kg)
Practice
 A solution was prepared by dissolving
17.1 g of sucrose C12H22O11 in
125g of water. Find the molal
concentration
 Given Solute mass = 17.1g sucrose
 Solvent mass = 125 g H2O
Colligative Properties
 Boiling- point elevation
 Freezing-point depression
 Vapor-pressure lowering
 Osmotic pressure
 These change in relation to the total
number of solute particles present
 They are a constant that can be used to
calculate the changes in solvents that
contain nonvolatile solutes
 Electrolytes have greater affects on
colligative properties