Transcript Chapter 4: Ionic Bonding - Research at OSU Chemistry

Chapter 12:
Solutions
Chem 1110
Figures: Basic Chemistry 3rd Ed., Timberlake and Timberlake
Examples of Common Solutions
Solid Solutions:
• Brass (65% Cu, 35% Zn)
• White Gold (60% Au, 40% Pt)
Liquid Solutions:
• Vinegar (95% water, 5% acetic acid)
• Solutions used in lab
Gas Solutions:
• Air (78% N2, 20% O2, 1% Ar, 0.5% CO2, 0.5% H2O)
Solutions
We need to define the important components
in a solution:
• Solvent: The most abundant substance in
a solution
• Solute: Any substance dissolved in the
solvent
• Aqueous Solution: a solution of any solute
in water. Water is the solvent.
Solid Solutions
Solid Solutions: An Alloy is a solid solution
of metals:
• Brass (65% Cu, 35% Zn)
• White Gold (60% Au, 40% Pt)
• If one of the metals is mercury (Hg) we call
this solution an amalgam
• Amalgams were commonly used in older
dental work
Solutions
Concentration is the amount of solute in a
given volume of solution
• Concentrated Solution has a large amount
of solute per volume
• Dilute Solution has a small amount of solute
• This is a Qualitative distinction, of course we
will have to consider Quantitative values
Saturated Solutions
We can add solute to a
solvent until NO more solid
will dissolve to form a
Saturated Solution
• Saturation defines the
solubility of the solute
• Solubility is the maximum
amount of solute that can
be dissolved in a given
solvent
Solubility
Solubility is based on:
1. Pressure applied to the system
2. Temperature of the solution
3. Nature of the solvent and solute interaction
Solubility in Water
Solubility increases as temperature increases:
Supersaturated Solutions
If we heat a saturated solution to dissolve
more solute, we can create a Supersaturated
Solution:
• Supersaturated Solutions are:
• An Unstable State because there is too much
solute for the amount of solvent
• Will precipitate out very easily
• Used to make hot packs for injuries
Solubility
Temperature and Pressure affect solubility:
• For solid or liquid solutes:
• Increasing T, increases solubility
• Supersaturated Solution
• Increasing P has NO effect on solubility
• For a gaseous solute:
• Increasing T, decreases solubility
• Increasing P, increases solubility
 Henry’s Law
Attractive Forces in Solutions
Interactions between solutes and solvents that:
• are similar in polarity will form a solution
• are not similar will not form a solution
“Like dissolves like”
Water as a Polar Solute
Solubility
Two liquids that dissolve into each other are
said to be miscible
• If you consider Intermolecular Forces:
“Like dissolves like”
 Ethanol and water are miscible
 Hexane and water are immiscible
Like Dissolves Like
Solvents
Solutes
Water (polar)
CH2Cl2(nonpolar)
Ni(NO3)2
(polar)
I2 (nonpolar)
Units of Concentration
We report the concentration of solutions in
many different units:
• There are several important Career specific
units to consider:
• Percent by Mass (m/m)
• Percent by Volume (v/v)
• Concentrations in chemistry are most often
reported in Molarity (M)
Percent by Mass
Percent by Mass (m/m) is used most often in
engineering or agricultural applications
• Commonly measured in grams
Percent by Mass = mass of solute x 100%
mass of solution
• 6.0 % (m/m): 6.0 g of solute dissolved in a total
of 100 g of solution (6 g solute and 94 g solvent)
Percent by Mass
Low fat milk has 1% (m/m) milkfat
• This means that in this sample of
milk there is…
© Brooks/Cole, Cengage Learning. All rights reserved.
Percent by Volume
Percent by Volume (v/v) is used most often when
both solute and solvent are liquids or gases:
Percent by volume = volume of solute x 100%
volume of solution
• 17.0 % (v/v): 17.0 mL of solute dissolved in a
total of 100 mL of solution (17 mL solute and 83
mL solvent)
Percent by Volume
Rubbing alcohol is 70% (v/v)
isopropanol in a solution with water
• This means that in the bottle
there are…
© Brooks/Cole, Cengage Learning. All rights reserved.
Molarity
Molarity (M) is the unit of concentration most
often used in chemistry labs:
Molarity (M) = moles of solute
1 liter of solution
• A solution that has 1 mole of solute dissolved in a
total of 1 liter of solution is said to be 1 molar (1 M)
Molarity (M) = moles
liter
Learning Check
How many grams of CuSO4 (159.10 amu) are needed
to make exactly 500 mL of a 1.00 M solution?
Learning Check
How many moles of CuSO4 are in 150 mL of
the 1.00 M solution?
Dilution
We decrease the concentration (or dilute)
aqueous solutions by adding water
• The moles of solute STAYS THE SAME
• The volume of the solution changes
• Results in a change of molarity (M)
 Molarity decreases
Dilution
In a dilution:
• water is added
• volume increases
• concentration decreases
Dilution
Initially:
Molarity (M1) x volume (V1) = # moles solute
After Dilution:
New molarity (M2) x volume (V2) = # moles solute
# moles solute = # moles solute
M1V1 = M2V2
V2 = V1 + Vadded
Dilution
What is the molarity of a the final solution after diluting
150 mL of a 1.0 M CuSO4 solution with 200 mL of
water?
Molarity in a Chemical Equation
How many milliliters of a 3.00 M HCl solution
are needed to react with 4.85 g of CaCO3?
2HCl(aq) + CaCO3(s)
CaCl2(aq) + CO2(g) + H2O(l)
Learning Check
How many liters of H2 gas at STP are produced when
6.25 g of Zn react with 20.0 mL of a 1.50 M HCl
solution?
Zn(s) + 2 HCl(aq)
ZnCl2 (aq) + H2(g)
Colligative Properties
Homogeneous solutions may have different physical
properties than the pure substances that they contain
• Properties of substances in a solution may be
different:
– We will talk about adding nonvolatile solute leads to
• Increased melting point
• Increased boiling point
• Decreased vapor pressure
Colligative Properties
Colligative Properties are properties of
solutions that depend on the number of
particles dissolved in the solvent
• Colligative Properties do not depend on
the identity of the particle:
o Ions
o Covalent Molecules
• It is the concentration of particles that
matters, particle molarity
Colligative Properties
Dissolved Particles in a solution:
• 1 sugar molecule → 1 sugar molecule
o Total of 1 particle in solution
• 1 NaCl formula unit → 1 Na+ ion + 1 Cl- ion
o Total of 2 particles in solution
• (NH4)3PO4 →
Particle Molarity
Dissolved Particles in a solution:
• 1 M sugar molecule → 1 M sugar molecule
o Total of 1 M particles in solution
• 1 M NaCl formula unit → 1 M Na+ + 1 M Clo Total of 2 M particles in solution
• 1 M (NH4)3PO4 → 3 M NH4+ + 1 M PO43o Total of 4 M particles in solution
Learning Check
What is the molarity of particles in a solution of 125 g
of MgCl2, a strong electrolyte, dissolved in 0.500 L of
water?
Colligative Properties
A large number of solute particles may cause
interruptions or “get in the way” of the solution
surface:
• Dissolved particles may disrupt intermolecular
forces
• The pure substance is “diluted” by the solute
• Decrease solvent-solvent interactions on the
surface
Colligative Properties
Solute particles (ionic or molecular) can:
• Interrupt the intermolecular forces holding the
molecules of a solvent together
• Weaken the intermolecular forces of the solvent
• “Get in the way” on the surface of a solution
and make it more difficult for molecules to
escape
Colligative Properties
Colligative Properties may include:
1. Boiling Point Elevation
2. Freezing Point Depression
3. Osmotic Pressure
Colligative Properties
Effect on Boiling Point…
It is common to add salt to water when boiling, why?
• Adding a non-volatile solute may lower vapor
pressure
• Ions interfere with solvent-solvent interactions on
the surface
• Ions make it harder for water molecules to escape
– Fewer solvent (water) particles on the surface
Colligative Properties:
Boiling Point Effects
• Ions make it harder for water molecules to escape
– Fewer solvent (water) particles on the surface
Colligative Properties
Boiling Point Effects:
• A higher temperature is needed to get the vapor
pressure to equal atmospheric pressure
• DECREASE the vapor pressure of the solution
• INCREASE the boiling point of the solution
• INCREASE number of particles for a larger effect
• Adding salt to water raise boiling temperature:
1 mole of particles raises boiling point by 0.52 °C
• Antifreeze in car engines raises boiling point in
radiator
Colligative Properties
Effect on Freezing Point…
Why do we add salt to roads in winter?
• Salt interferes with intermolecular forces
holding the H2O molecules together
• Water molecules are not able to organize
into ice crystals since solute is in the way
• A lower temperature is needed to reach
the solid state
• The Freezing Point is DECREASED
Colligative Properties
Why do we add salt to roads in winter?
• Salt interferes with intermolecular forces holding
the H2O molecules together
• Water FREEZES at a lower temperature
• Salt prevents roads from re-freezing but it DOES
NOT melt the ice!!
• CaCl2 (Ice Melter®) melts ice and lowers the
melting temperature even colder
The oceans never freeze solid due to higher
salt concentrations
Osmosis
OSMOSIS: the transport of a solvent across a
semi-permeable membrane
• We will limit our discussion to water as the solvent
• Water moves across the membrane to create an
isotonic system
Example of Osmosis
A semi-permeable membrane separates a 4% starch solution
from a 10% starch solution. Starch is a colloid and cannot
pass through the membrane, but water can. What happens?
4% starch
10% starch
H2O
Semi-permeable membrane
Example of Osmosis (continued)
The 10% starch solution is diluted by the flow of water
out of the 4% solution, and its volume increases
• The 4% starch solution loses water, and its volume
decreases
• Eventually, the water flow between the two becomes
equal
7% starch
H2O
7% starch
H2O
Osmotic Pressure
• Water flows from less concentrated to more
concentrated side of a semi-permeable
membrane
• Movement of water molecules sets up a
pressure differential
• Osmotic Pressure is the pressure required
to make these two sides equal equilibrate
Hypotonic, Hypertonic,
Isotonic Solutions
• Maintaining appropriate solution conditions
are very important in your body and chemistry
• Consider the possible negative effects…
Isotonic Fluid
Consider, an isotonic solution such as blood:
Blood plasma (liquid) should have the same
osmotic pressure as in your red blood cells:
o 5.0% (m/v) glucose
o 0.9% (m/v) NaCl
Red Blood Cell: Isotonic Solution
Dr. Stanley Flegler/Getty Images
• Composition of cell is similar to the isotonic
solution it is in – no significant osmosis
Red Blood Cell in Hypotonic Solution
Hemolysis
David H. Phillips/Photo Researchers
• Water flows into the cell to dilute the solution
inside (from the hypotonic solution)
Red Blood Cell in Hypertonic Solution
Crenation
David H. Phillips/Photo Researchers
• Water flows out of the cell to dilute the
hypertonic solution outside
Colloidal Solution
• A homogeneous mixture, NOT a true solution
o No solute or solvent
• Contains dispersed particles that
are intermediate in size between
those of a solution and those of an
ordinary heterogeneous mixture
• So, have dissolved solids in solvent
o Fog
o Milk
Tyndall Effect
• Colloidal Solutions scatter light (Tyndall Effect):
True Solution:
No Scattering
Colloidal Solution:
Light Scatters
Suspension
Suspension: a heterogeneous mixture
containing dispersed particles that are
heavy enough to settle out under the
influence of gravity:
• Muddy water
• Blood
• Fine precipitates
Colloidal Dispersion
Suspension
• Homogeneous
• Heterogeneous
• Groups of small particles
or individual larger
molecules
• Very large particles, which
are often visible
• Not transparent
• Scatters light (Tyndall
effect)
• Particles settle rapidly
• Particles do not settle
• Particles can be filtered out
• Particles cannot be
filtered out
Solutions, Colloids, and Suspensions
Dialysis
• Dialysis is similar to osmosis
• Uses a semi-permeable membrane that allows
the passage of solvent, dissolved ions, and
small molecules, but blocks the passage of
colloidal-sized particles and large molecules:
Removing Colloidal Impurities
Artificial Kidney Machine