Transcript
SOLUTIONS “If you’re not part of the solution, you’re part of the
precipitate”
Properties of Solutions
Definition of a Solution: a homogeneous
mixture of substances in the same physical
state
What does Homogeneous mean?
atoms, ions, or molecules of one
substance spread uniformly throughout
a second substance
Types of Solutions Solutions exist in all three states (solid, liquid
and gas).
What is it called when metals are mixed to form a solid solution? alloy
ex. brass = Cu/Zn; steel = iron + carbon
What is an example of gases forming a solution? Air (is a homogeneous mixture)
The majority of this topic will be limited to only liquid solutions, in which a solid is dissolved in a liquid.
• ex. salt water, antifreeze
1. Solute substance being dissolved; smaller amount.
2. Solvent substance doing the dissolving; larger amount
Salt in salt water Sugar in soda drinks
Carbon dioxide in soda drinks
Water in salt water Water in soda
What is the most common solvent? Water What are these types of solutions called Aqueous
solutions and what is the notation used (aq)?
What makes a SOLUTION
Concentrated vs. Dilute
Write an example equation of a substance being dissolved in water:
Dissociation - ionic solid separating into ions
NaCl(s) Na+(aq) + Cl
–(aq)
hydrated ions
LiCl(s) Li+(aq) + Cl–(aq)
5 Main points about all
liquid solutions…..
1.Solutions are homogeneous mixtures (aq) –known as true solutions
2.Solutions are clear & do not disperse light
3.Solutions can have color
4.Solutions will not settle upon standing
5.Solutions will pass through a filter
Solubility Factors
Define Solubility: amount of solute that will dissolve in a certain amount of a solvent at a certain temperature
Materials with high solubility are said to be SOLUBLE (aq)
Materials with low solubility are said to be INSOLUBLE (s) –precipitate out
Use Table F (Solubility Guidelines) – see pg 4 of guide for practice
THE NATURE OF SOLUTE AND SOLVENT
Draw the dissolving process of NaCl in water - dissociation
• The positive ends of the Na+ are attracted to the NEGATIVE end of the water molecule.
• The negatively ends of the Cl- are attracted to the POSITIVE end of the water molecule.
• Opposites ends attract
NaCl (s) Na+ (aq) + Cl
– (aq)
• This dissolving process of a solid in water is called HYDRATION or
SOLVATION
• What does the phrase “Like dissolves like ‘ mean? DESCRIBES WHAT
SOLUTES WILL DISSOLVE IN WHAT SOLVENTS
Ex of Ionic Solvation Ex of Molecular (covalent) Solvation
(molecules stay intact)
NaCl (s) Na+ (aq) + Cl–
(aq) C6H12O6 (s) C6H12O6 (aq)
Solvation and Conductivity
Strong
Electrolyte
Non-
Electrolyte
solute exists as
ions only
- +
salt
- +
sugar
solute exists as
molecules only
- +
acetic acid
Weak
Electrolyte
solute exists as
ions and
Molecules
Salts dissociate
Covalent (nm + nm)
Includes acids
Ionic (m + nm)
Electrolyte = conductor
Fill in the Solubility Summary
based on similar attractive forces
“Like Dissolves Like”
Solute type nonpolar solvent
(soap)
polar solvent
(water)
Nonpolar (oil)
soluble Insoluble
Polar (sugar)
insoluble soluble
Ionic (salt)
insoluble soluble
Variables: see table G
1. Temperature
As temperature increases, most solids become more soluble in water.
As temperature increases, most gases become less soluble in water.
• Think warm soda pop
• solids are more soluble at high temps.
2. Pressure
Pressure has little or no effect on the solubility of solid or liquid solutes.
Pressure does affect the solubility of gases in liquids. As pressure Increases, the solubility of gases in a liquid increases.
gases are more soluble at low temps & high pressures
Graphs – Table G
pressure
Sol
(g)
Sol
(L & S) Sol
(g)
Temp temp
inc P, inc sol inc T, dec sol inc T, inc sol
A cube of sugar
in cold tea
dissolves
slowly. .
Granulated sugar
dissolves in cold
water more quickly
than a sugar cube,
especially with stirring
Solution Formation
Granulated
sugar dissolves
very quickly in
hot tea
RATE OF SOLUTION
Factor
Affect on Solid Solute
Affect on Gaseous Solute In a confined space
Crushing
reducing particle size increases the rate by increasing surface area (causing more collisions)
not applicable
Stirring
increases the rate by exposing fresh solvent to solute and increasing kinetic energy (motion of particles)
decreases the rate by increasing kinetic energy, thereby reducing solubility
Amount of dissolved solute
as the amount of dissolved solute increases, the rate decreases
as the amount of dissolved solute increases, the rate decreases
Temperature
as the temp increases, the rate increases due to increasing kinetic energy causing molecules to collide more frequently
as the temperature increases, the rate decreases solubility
Shows the relationship between temp and solubility of a solute
Table G (based on 100g of water)
Solids increase temp, increase solubility Solid line
Gas: increase temp, decrease solubility Dotted line
Saturation & Solubility Curves
Saturation
•A solution that contains the maximum amount of solute in a given amount of solvent. •On the reference line
the rate of dissolving equals the rate of crystallization (equilibrium), so the total amount of dissolved solute remains constant
NaCl(s) NaCl(aq)
Implies equilibrium
Saturated Solutions
dissolving
crystallization
Unsaturated
A solution that
contains less
solute than a
saturated solution
under existing
conditions is
unsaturated.
Below the
reference line
Supersaturated
A supersaturated solution is clear before a seed crystal is added.
Crystals begin to form in the solution immediately after the addition of a seed crystal.
Supersaturated
Excess solute crystallizes rapidly
Practice Question #1
1) According to Reference Table G, which compound solubility decreases most rapidly as the temperature changes from 10°C to 70°C?
a) NH4Cl
b) NH3
c) HCl
d) KCl
Answer to problem #1
Correct Answer Number: 2
Explanation: See Ref. Table G.
Notice the curves for choices 1 and
4 increase. Choice 2 and 3 both
decrease but choice 2 (NH3)
decreases more than 50 degrees,
while HCl decreases only about 16
degrees.
Molarity
• The concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solvent.
– A dilute solution is one that contains a small amount of solute.
– A concentrated solution contains a large amount of solute.
Concentrations of Solutions
• Water must be tested continually to ensure that the concentrations of contaminants do not exceed established limits. These contaminants include metals, pesticides, bacteria, and even the by-products of water treatment. You will learn how solution concentrations are calculated.
Quantities in Solutions
The amount of solute in a solution.
Describing Concentration
• % by mass - medicated creams
• % by volume - rubbing alcohol
• ppm, ppb - water contaminants
• molarity - used by chemists
• molality - used by chemists
Molarity
• Molarity (M) is the number of
moles of solute dissolved in one
liter of solution.
• To calculate the molarity of a solution,
divide the moles of solute by the volume of
the solution.
Molarity
• To make a 0.25 molar (0.25M) solution, first
add ? mol of solute to a 0.50-L (500mL)
volumetric flask half filled with distilled water.
Solve for Moles
Solute used is NaCl
We want to prepare 500 mL of a 0.25
Molar solution
Using the Molarity formula solve for
moles of solute
M = Moles of Solute
Liters of Soln
Plug in Numbers
0.250 mol/Liter = x moles
0.500L
# of Moles = 0.250mol/liter x 0.500 L
x = 0.125 moles
Convert Moles to Grams
0.125 moles NaCl ? Grams
Use Mole Conversion Formula
Moles = given mass
gfm
Plug in Numbers
0.125 moles = x grams
58 g/mol (gfm of NaCl)
X= 7.25 grams NaCl
Molarity
• Add 7.25 grams of NaCl to water in flask
• Swirl the flask carefully to dissolve the solute.
Molarity
• Fill the flask with water exactly to
the 500-mL mark.
16.2
#1: How many moles of NaOH are contained in 200 ml of 0.1M solution of NaOH?
2) Which solution is the most concentrated?
a) 1 mole of solute dissolved in 1 liter of solution?
b) 2 moles of solute dissolved in 3 liters of solution?
c) 6 moles of solute dissolved in 4 liters of solution?
d) 4 moles of solute dissolved in 8 liters of solution?
Answer:
moles = (M)(L)
= (0.1 M)(.2L)
=.02 mol
Correct Answer Number: 3 Explanation: #3 (1.5 M. ) is the most concentrated. Find the molarity ( moles of solute/liter of solution) for
each answer.
#1) 1 mole / 1 liter or 1 M. #2) 2 moles / 3 liters or 0.67 M. #3) 6 moles / 4 liters or 1.5 M. #4) 4 moles / 8 liters or 0.5 M.
Answer:
M = (moles)/(L)
= 1.50 moles
.5000L
= 3.00 M
Ex #2: What is the molarity of a 500.0 mL solution of NaOH (GFM = 40.0g) with 60.0 g of NaOH (aq)?
Different style problem
1) Which solution is the most concentrated?
a) 1 mole of solute dissolved in 1 liter of solution?
b) 2 moles of solute dissolved in 3 liters of solution?
c) 6 moles of solute dissolved in 4 liters of solution?
d) 4 moles of solute dissolved in 8 liters of solution?
Answer to different style problem
Correct Answer Number: 3 Explanation: #3 (1.5 M. ) is the most concentrated. Find the molarity ( moles of solute/liter of solution) for
each answer.
#1) 1 mole / 1 liter or 1 M. #2) 2 moles / 3 liters or 0.67 M. #3) 6 moles / 4 liters or 1.5 M. #4) 4 moles / 8 liters or 0.5 M.
Percent Solutions
• Concentration in Percent
(Volume/Volume)
16.2
Percent Solutions
• Isopropyl alcohol (2-propanol) is sold as a 91%
solution. This solution consist of 91 mL of
isopropyl alcohol mixed with enough water to
make 100 mL of solution.
16.2
Percent Solutions
Percent Solutions
Percent Solutions
• Concentration in Percent (Mass/Mass)
16.2
A 50.0 gram sample of a solution is evaporated and found to contain 0.100 grams of sodium chloride. What is the percent by mass of sodium chloride in the solution?
% mass = 0.100 g X 100
50.0 g
= 0.200%
100.0 grams of water is evaporated and analyzed for lead. 0.00010 grams of lead ions are found. What is the concentration of the lead, in parts per million?
ppm = grams of solute x 1,000,000 grams of solution = (0.00010 g) x 1,000,000 100.00010 g = .9 ppm •If the legal limit for lead in the water is 3.0 ppm, then the water sample is within the legal limits (it’s safe and ok)
Colligative Properties of
Solutions
The wood frog is a remarkable creature because it
can survive being frozen. Scientists believe that a
substance in the cells of this frog acts as a natural
antifreeze, which prevents the cells from freezing.
You will discover how a solute can change the
freezing point of a solution.
16.3
Colligative Properties
depend on the number of particles (molality) rather than the nature of the particles in the solution.
Boiling point, freezing point, vapor pressure and osmotic pressure are some of the properties affected.
Boiling Point Elevation
BP of a solution is higher than BP of the pure solvent
Solute particles weaken IMF in the solvent
Freezing Point Depression
• f.p. of a solution is lower than f.p. of the
pure solvent
Vapor-Pressure Lowering
• In a solution, solute particles reduce the number
of free solvent particles able to escape the liquid.
Equilibrium is established at a lower vapor
pressure.
16.3
Vapor-Pressure Lowering
Three moles of
glucose dissolved in
water produce 3 mol
of particles because
glucose does not
dissociate.
16.3
Three moles of
sodium chloride
dissolved in water
produce 6 mol of
particles because
each formula unit of
NaCl dissociates into
two ions.
Three moles of calcium
chloride dissolved in
water produce 9 mol of
particles because each
formula unit of CaCl2
dissociates into three
ions.
Applications
• salting icy roads
• making ice cream
• antifreeze
•cars (-64°C to 136°C)
•fish & insects
Colligative Properties con’t.
• # of Particles
• Nonelectrolytes (covalent) – remain intact when dissolved – 1 particle
• Electrolytes (ionic) – dissociate into ions when dissolved – 2 or more particles
Boiling point elevation
called molal boiling point elevation (Kb).
It is proportional to the concentration of dissolved particles
1 mole of particles in solution raises the BP of water by 0.52 C
Which 1 molal solution will have the highest boiling point?
KNO3 Mg(NO3)2 Al(NO3)3
Freezing Point
Depression
called molal freezing point depression (Kf).
1 mole of particles in solution depresses the FP of water by 1.86 C
What will depress the FP of water the most….AlCl3or MgCl2? Why? What would the new FP be?
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