Transcript Solutions

Solutions
Solution = Solvent + Solute
• Solvent: a substance
that dissolves another
substance
– Or, the substance
present in greater amount
• Solute: a substance
which is dissolved by
another substance
– Or, the substance
present in lesser amount
•
Copper (II) Sulfate is dissolved in water to
form a solution. Which substance is the
solvent and which is the solute?
• Water is sometimes
called the “Universal
Solvent”
– It is the most
common solvent in
nature/biological
systems
• Why do you think
water is such a good
solvent?
– Polarity
– Hydrogen bonding
• The positive end of water molecules are attracted to
the negative part(s) of the solute
• The negative end of water molecules are attracted to
the positive part(s) of the solute
• The attraction of water molecules to different parts of
a solute is enough to break the solute apart
• As each ion in
the solute is
drawn into
solution, it is
surrounded by
water molecules
• This process is
called “solvation”
• Solvation lessens
the attraction of
the solute ions to
each other
• If water is the universal solvent,
then why does it not dissolve
oil?
• For a solution to form, the
solvent and solute molecules
must be attracted to each other
• “Like Dissolves Like”
• Polar solvents dissolve polar
solutes
• Nonpolar substances are
attracted to other nonpolar
substances, therefore nonpolar
solvents will dissolve nonpolar
solutes
– Examples: I2, Hexane, Cooking
Oils, Dichloromethane (CH2Cl2)
Problems
1) Identify the solute and solvent in solutions
composed of the following:
a) 2.9g of NaCl and 200g H2O
b) 25.0mL of ethanol (a liquid) and 20.0mL H2O
c) 2.0g I2 and 20g Octane
2) Look at the pictures below. Explain why each
substance will or will not dissolve in water.
Solubility
• Solubility: the amount of solute that
will dissolve in a specific solvent
under given conditions
– Polar solutes will be more soluble in
polar solvents
– Non-polar solutes will be more soluble in
non-polar solvents
– Amphiphilic solutes will be soluble in
both polar and non-polar solvents
• Have hydrophobic and hydrophilic
regions
– Example: Phospholipids
• Solubility is expressed in
g solute/100g solvent
– Example: The solubility of
Ethanol is 10g/100g H2O @
23ºC
• Unsaturated Solution:
solution in which the
solvent can dissolve more
solute
• Saturated Solution:
solution in which the
solvent cannot dissolve
any more solute
• When a solution is saturated, the rate of
dissolution is the same as the rate of
recrystallization/precipitation
• Say we have a
saturated sugar
solution. How might
we get even more
sugar into the
solution?
• Heat it!
• Solubilities of solids
generally increase as
the temperature
increases
• Supersaturated solution: an unstable
solution which temporarily contains more
dissolved solute than a normal saturated
solution would at that specified temp
• What about if you
wanted to dissolve
more oxygen in your
water? Would you
heat your water?
• No!
• The solubility of
gases tend to
decrease as the
temperature is
increased
• So, how do you increase the solubility of gases in a
liquid?
– Decrease the temperature
– Increase the pressure
• Henry’s Law: the solubility of a gas in a liquid is
directly proportional to the pressure of that gas above
the liquid
Soluble and Insoluble Salts
• How do you know that NaCl is soluble
in water?
• What about KBr? Is it soluble?
• What about AgCl?
• You can tell if a salt will be soluble or
insoluble in water by looking up the
cation and the anion on a solubility
chart
Problems
1) Is the CO2,which is dissolved in soda, more or
less soluble when you open the can? Why?
2) Which of the following is probably Ni(OH)2 in
water?
3) Which is most likely Na2SO4 in water?
Problems
Which of the following salts is soluble in
water? Which is insoluble?
1) NaCl
2) KBr
3) AgCl
KBr
NaCl
AgCl
Problems
Which of the following salts will be soluble in
water? Which will be insoluble?
1) Ag2O
2) CdS
3) Fe(OH)2
4) Na2SO4
5) KCl
CdS
Ag2O
Fe(OH)2
Na2SO4
KCl
Concentrations
• Concentration = amount solute/amount
solution
• There are various ways to express
concentration
• The most common way to express
concentration is Molarity (M)
• Molarity = moles solute/liters solution
• Units: mol/L
Problems
1) You dissolve 5.66g KBr in enough H2O
to make 27mL of solution. What is the
molarity of your solution?
2) You dissolve 2.45 mg of CuSO4 in
enough water to make 55.5 mL of
solution, what is your concentration?
3) If you have 60.0 mL of a 0.988 M NaCl
solution, how much NaCl did you start
with?
• Mass-volume percent (% m/v): mass of the solute
divided by the volume of solution and multiplied by 100
• % m/v =(mass solute)/(volume solution) x 100
• Also defined as mass of solute per 100 ml of solution
• Usually expressed in g/ml
Problems
1) You dissolve 5.66g KBr in enough H2O to make
27mL of solution. What is the mass/volume
percent for the previous solution?
2) You dissolve 4.44 g NaCl in enough water to
make 0.075 L of solution. What is the massvolume percent?
3) You have a % m/v of 3.98 NaBr in 350 ml of
solution. How much NaBr was used to make this
solution?
• Percent by Mass (%m/m): mass of solute in mass of
solution multiplied by 100
• Mass % = mass solute/mass solution x 100
• Remember: mass solution=mass solute + mass
solvent
• Also defined as the number of grams of solute per
100g of solution
Problems
1) You make a solution by dissolving 7.55 g NaCl in
52.4g H2O. What is the mass % of solute in this
solution?
2) You make a solution by dissolving 2.45 g KCl in
20.6mL of water. What is the mass % of solute in
this solution?
3) You have a %m/m of 10.0% sucrose. If you used
25.0 g sucrose to make the solution, how much
solvent (water) did you use?
• Percent by volume (% v/v): volume of solute divided by
volume of solution multiplied by 100
• VP = volume solute/volume solution x 100
• Units of volume must be the same for both solute and
solvent
Problems
1) You dissolve a 5 cm3 cube of sugar in 20mL of
water. What is your volume percent of solute in
this solution?
2) Your bottle of Jack Daniels says that the alcohol
content is 14%. What does this mean?
More Problems
1) Your child has an ear infection and is
given a suspension of 5.0 % (m/v)
amoxicillin. How many grams of the
antibiotic is she given in 10mL?
2) How many milliliters of a 4.0% (m/v) drug
are needed if the patient is to receive
0.250g?
Dilutions
• Dilution: the process by which more
solvent is added to a solution in order to
lower the concentration
• C1V1 = C2V2
• C = Concentration
• V = Volume
Problems
1) Joan has 50 mL of a 0.498 M glucose solution.
She’d like to dilute this to a 0.250 M glucose
solution. What will her final volume be?
2) A nurse wants to prepare a 1.0% (m/v) silver
nitrate solution from 24 mL or a 3.0% stock
solution of silver nitrate. How much water
should be added to the 24 mL?
3) Mary has a 2.5 L bottle of a 0.989 M NaOH
solution. She would like to make 525 mL of a
0.755 M NaOH solution. How will she do this?
Mixtures
• Heterogeneous Mixture: a mixture in which
the particles of each component remain
separate and can be observed as
individual substances
– See distinct phases
– See interface
– Solute particle size above 200nm
• Homogeneous Mixture: a mixture in which
the composition is the same throughout
– Only one phase present
– Cannot see interface
– Particle size less than 1nm
– Often called “solutions”
Colloids
• Mixtures with properties intermediate between
heterogeneous and homogeneous mixtures
• Particles tend to be small enough to pass
through filters, but too large to pass through
semipermeable membranes (1nm-200nm)
• Particles are large enough to scatter light,
producing a phenomenon called the Tyndall
effect
• Examples: Jell-O, Fog, Dust in air, Mayo
The Tyndall Effect
• Named after the Irish
scientist John Tyndall
• Describes the light
scattering effect cause by
particles in a colloid
– Can see the beam of light
– Can see the particles in
the colloid
• Used to distinguish
colloids from other types
of mixtures
Suspensions
• Heterogeneous mixtures
which contain particles which
are large enough to be
trapped by filters and
semipermeable membranes,
but small enough to stay
suspended for a while before
settling out.
• Examples: Muddy water, liquid
medications, paint
– Most things that direct you to
shake or stir before using
Osmosis
• The movement of
water, through a
semipermeable
membrane, from
regions of low solute
concentration to
regions of higher
solute concentration
• Spontaneous
• The membrane must
be permeable to the
solvent, but not the
solute
• Movement of water to one side of the permeable
membrane causes osmotic pressure
• Osmotic
Pressure is defined as
the force per unit area that
prevents water from passing
through a membrane
• In living systems, osmotic
pressure is called turgor
– Pressure of intracellular water
and other contents press up
against the cell membrane
causing the cell to expand
– Plant cells are prevented from
rupturing by their cell walls
– Allows plants to stand upright
• What problems does osmosis present to
aquatic and marine life?
• Hypotonic solution: a situation
in which the concentration of
solute(s) is higher inside the
membrane/cell than in the
surrounding solution
– Water flows into the cell by
osmosis
– Causes turgor and/or cell lysis
• Hypertonic solution: a
situation in which the
concentration of solute(s) is
lower inside the
membrance/cell than in the
surrounding solution
– Water flows out of the cell by
osmosis
– Causes cell shrinkage called
crenation
• Isotonic solution: a
situation in which
the solute
concentrations on
the inside and
outside of a
membrane/cell are
equal
• There in no NET
movement of
water
• Also called
“Physiological
Solutions”