Solutions
Unit: Solutions
Topic: Molarity
Objectives: Day 1 of 3
• To understand the difference between a solvent
and solute
• To understand the process of dissolution
• To understand how polar and nonpoloar
substances dissolve
• To understand Molarity in terms of solution
concentration
• To understand how to calculate Molarity given
moles, volume or molarity (M)
Quickwrite
Please answer any of the questions below in 1-2
sentences:
• Why do you solids such as salt and sugar
disappears when the are added to water???
• As these substances dissolve, what do you think is
happening on a molecular level????
• What do you think is more concentrated, a 1 liter
glass of water with 1 cup of sugar dissolved in it,
or a 1 liter glass of water with 2 cups of sugar
dissolved in t??
Solutions
• Most of the important chemistry that keeps
plants animals and humans alive takes
place in aqueous solutions
• Even water that comes our of your faucet
is a solution because it has dissolved
minerals in it
Solutions
• If you recall, a solution is a homogeneous mixture in
which the components are uniformly intermingled
• Salt water is homogeneous mixture in which the first sip
will be the same as the last sip
• Solutions can be solids and gases as well
• Consider brass, brass is a solution made up of copper
and zinc
• A gaseous solution would be air
• Air is made up of mostly nitrogen(80%) and oxygen
(20%)
What is a Solution?
• a ______ mixture of ___or more
substances (usually liquid)
• Ex: solution of sugar and water
Answer Bank
Largest
concentration
dissolve(s)
Homogeneous
Lesser
Polar
Higher
Surface
Crystal
Temperature
Two
Solutions
• The substance present in the largest
amount is called the solvent (usually water)
• The other substance in lesser amounts is
called the solute
What is the difference between a
solvent and a solute?
• The substance present in the
_____amount is called the
solvent (usually water)
• The other substance in
____amounts is called the solute
Answer Bank
Largest
concentration
dissolve(s)
Homogeneous
Lesser
Polar
Higher
Surface
Crystal
Temperature
Two
Practice:
Complete the table by identifying the solvent and solute for each solution:
In the solution below, determine
1. Coffee solution made up of
98.75% water and the rest
consists1.25% of other
chemicals
2. Cola is a solution made up
of about 11 % sugar and
roughly 88% water
3. Vinegar is a solution made up
of 3.5 % acetic acid and 96.5%
water.
Solvent
Solute
Water Polarity
• Remember, a water
molecule has a
negative and positive
dipole or charge to it
• The oxygen atom gives
it a slight negative
charge while the two
hydrogen atoms give it
a slight positive charge
• These strong charges
rip and remove sodium
and chlorine atoms
individually
+
-
+
When a compound such as salt dissolves in
water we call this solvation
• Let’s see what
happens when salt
dissolves in water……
+
+
+
-
+
+
+
+
+
-
+
-
-
What is Dissolution?
• The process by which a compound
such as salt _____in water
Answer Bank
Largest
+1
-1
• NaCl  Na + Cl
concentration
dissolve(s)
Homogeneous
Lesser
Polar
Higher
Surface
Crystal
Temperature
Two
Polar vs. Nonpolar
H2O = polar
electrons shared unequally
resulting in a slight positive
charge and a slight
negative charge
asymetrical geometry
CH4 methane = nonpolar
electrons shared equally
No charge
symetrical geometry
What’s the difference between
polar and non-polar molecules?
H2O = polar
electrons shared unequally
resulting in a slight positive
charge and a slight
negative charge
asymetrical geometry
CH4 methane = nonpolar
electrons shared equally
No charge
symetrical geometry
Solubility of Polar Molecules
• Because water is a polar
molecule it can dissolve ions
such as chlorine and sodium
• But water can also dissolve
other nonionic molecules such
as ethanol, more commonly
known as alcohol
• Like water, Ethanol has a
polar O—H end to it with a
positive and negative charge
to it
+
-
+
+
Solubility of Polar Molecules
• Ethanol dissolves in water because it is polar molecule
• Polar molecules can dissolve other polar molecules
+
+
-
-
+
Hydrogen Bond
Solubility of Polar Molecules
• Because sugar and alcohol are both polar
molecules they are soluble (will dissolve in
water)
• Polar molecules will dissolve in another
polar liquid like water
• We say “like dissolves like”
• That is, polar molecules will dissolve other
polar molecules
Substances Insoluble in Water
• Many substances do not dissolve in
water
• For example oil does not mix with
water because it is made up of
nonpolar molecules
• The C—H bond has a low negativity
and the electrons are shared equally
• The result are nonpolar bonds that do
no mix with the polar water molecule
“Like” Dissolves “Like”
• One rule of thumb that chemists use and
worth remembering is “like dissolves like”
• In other words, polar molecules will
dissolve polar molecules and…..
• Nonpolar molecules will dissolve
nonpolar molecules
What’s the difference between
polar and non-polar substances?
• Polar substances will ______ in
_____substances
• Ex: (NaCl & water)
• Non-polar substances will not
______in Polar substances
• Ex: oil and water or vinegar “like
dissolves like!”
Answer Bank
Largest
concentration
dissolve(s)
Homogeneous
Lesser
Polar
Higher
Surface
Crystal
Temperature
Two
Molarity
• The most commonly used expression of
concentration when dealing with aqueous
solutions is Molarity (M)
• Molarity describes the amount of solute in moles
in the volume in liters
• Molarity is describes the amount of solute in
moles and volume of the solution in liters
• Molarity is define as the number of moles of
solute per volume of solution in liters, or….
• M = Molarity = moles of solute
liters of solution
What is Molarity (M)?
• The number of _____ of solute
per _____of solution in liters
• It measures solution _______
moles of solute
M = Molarity =
liters of solution
Answer Bank
liters
concentrated
Moles
concentration
Molarity(M)
volume
solute
Practice:
• Calculate the molarity of a solution
prepared by dissolving 11.5 grams of solid
NaOH in enough water to make 1.5 Liter
solution
We are given the following information:
Since
the molarity
requires
mole
and we are
Remember
the
definition
of Molarity:
1
mol
NaOH
11.5 g NaOH
given
gram,Mass
to convert
to mols
of
solute
=of
11.5
grams
M we
= need
moles
solute
=grams
0.288 mol NaOH
g NaOH
M = 40.0
moles
of solution
solute
liters
of
Volumeliters
of Solution
= 1.5 Liters
of solution
Now that we have mols we can solve for Molarity
M= moles of solute =
0.288 mol NaOH = 0.192 M NaOH
liters of solution
1.50 L of solution
Practice:
• Calculate the Molarity of a solution
prepared by dissolving 1.56 g of gaseous
HCl into enough water to make 26.8mL of
solution
We are given the following information:
Since the molarity requires mole and we are
Remember
the
definition
ofgrams
Molarity:
given
gram,
we
need
to
convert
to mols
1
mol
HCl
1.56 g Mass
HCl of solute = 1.56 grams
M
= 0.0427 mol HCl
M =
= moles
moles of
of solute
solute
36.5 g HCl
liters
of
Volume of
Solution
28.6 mL
liters
of=solution
solution
Now that we have mol we can solve for Molarity
Don’t forget to convert millileters into liters!
M= moles of solute =
0.0427mol HCl = 1.59 M HCl
liters of solution
0.0268Lof solution
Practice:
• How many grams of magnesium chloride
MgCl2 are needed to make 6.0 L of a 3.0
M solution?
Since
we
have
molarity
and
we have liters, we
We
are
given
the
following
information:
Remember the definition of Molarity:
To solve for moles and then convert to grams
M = moles
solute
95.3 g of
MgCl
=
moles
solute
Molarity of solution2 =of
3.0
M
=
1,715
g mol MgCl
liters liters
of solution
of solution
18 mol MgCl
M2
1 mol MgCl2
Volume of Solution = 6.0 L
Molarity only deal in Moles, so solving for moles we get:
3.0M =
mol MgCl2
6 L of solution
moles MgCl2 = (3.0 M)(6.0 L)
= 18 mol MgCl2
2
Summarize:
• Gases can be solutions. Air contains 21%O2 Answer Bank
liters
and 79% N2, so oxygen is the solute and
concentrated
___________is the solvent
moles
• In the expression like dissolves like, the word Molarity(M)
volume
like refers to similarity in molecular
Solute
___________.
Oxygen
Nitrogen
• Molarity is equal to ______ divided _____
polarity
• The more _________ a solution is, the higher
the ________
• Molarity describes the amount of ____in
moles in the volume in liters
Unit: Solutions
Topic: Standard Solutions
Objectives: Day 2 of 3
• To understand what factors increase the
rate of dissolution (dissolve)
• To understand how standard solution is
prepared
Quickwrite
Please answer any of the questions below in 1-2
sentences:
• If you wanted increase the rate at which sugar will
dissolve in your tea, what are some things you
could do to increase this rate of dissolution
(dissolve)????
• What do you think effects how fast salt will
dissolve in water?
• What do you think will dissolve faster in a cup of
water, a cube of sugar, or a spoon full of sugar???
Factors Affecting the Rate of
Dissolution
• 3 things to consider is surface area,
stirring, and temperature
Factors Affecting the Rate of
Dissolution
• When considering surface are,
smaller salt crystals will
dissolve faster than larger salt
crystals
• Temperature causes the
molecules to move faster
increasing te rate of dissolution
• Finally, stirring removes newly
dissolved particles from the
solid surface and continuously
exposes the surface to fresh
solvent (water molecules)
What factors affect the rate
of dissolution? Answer Bank
• 3 things:
– _____ area
– stirring, and
– __________
Largest
concentration
dissolve(s)
Homogeneous
Lesser
Polar
Higher
Surface
Crystal
Temperature
Two
Unsaturated Solutions
• A solution that has not reached the limit of
solute that will dissolve in it is said to be
“Unsaturated”
• In other words, it is a solution that is able
to dissolve more solute at that
temperature
• If we were to add more solute (salt), it would
continue to dissolve because the solution is
unsaturated
What is a Unsaturated Solution?
• A solution that is able to
____more solute at that_______
Answer Bank
Largest
concentration
dissolve(s)
Homogeneous
Lesser
Polar
Higher
Surface
Crystal
Temperature
Two
Saturated Solutions
• If you were to keep adding salt to water,
eventually it would stop dissolving
• There is a limit to how much solute can be
dissolved in a solvent (water)
• When a solution can no longer dissolve
the solute, we say the solution is
“saturated”
• That is, the solute (salt) will no longer
dissolve at a certain temperature
What is a Saturated
Solution?
• A solution in which the solvent
can ____no more of a specific
solute at a particular _______
Answer Bank
Largest
concentration
dissolve(s)
Homogeneous
Lesser
Polar
Higher
Surface
Crystal
Temperature
Two
Supersaturated Solutions
• Sometimes when a solid is
dissolved to the saturation level
at an elevated temperature and
then allowed to cool, all of the
solid may remain dissolved
• This type of solution is called a
supersaturated solution
• It contains more dissolved solid
than a saturated solution will
hold at that temperature
• A supersaturated solution is very
unstable, adding a crystal of the
solid will cause immediate
precipitation of a solid
Molarity Stoichiometry
• Because so many important reactions take
place in solutions, it is important to be able to
do stoichiometric calculations for solution
reactions
• Remember, molarity deals with moles, so if
you are given Molarity (M), and liters, you
should solve for moles
• A common mistake is to convert moles to
grams DO NOT DO THIS!!!!
Practice:
Consider the equation:
K2CrO4 + Ba(NO3)2  BaCrO4 + KNO3
You have 0.25 L of 0.5 M K2CrO4. How many
grams of 2KNO3 will be produced?
Now that we have moles of K2CrO4
First
calculate
the 98.2
moles
ofKNO
K
CrO
We
can
calculate
grams
of KNO
2
g
of
3
0.125 mol K CrO
3
2 mol KNO
=424.55
grams
2
4
3
of KNO3
1
mol
KNO
Solving for Moles of
K2CrO
becomes….
3
4, the molarity expression
1 mol
K2CrO
4
0.5 M =
mol K2CrO4
0.25 L of solution
moles K2CrO4 = (0.5 M)(0.25 L) = 0.125 mol K2CrO4
Practice:
• NaHCO3 + HCl  NaCl + H2O + CO2
• Sodium bicarbonate is used to neutralize an acid
spill. If there was 2.5 L of 0.1 M HCl, how many
grams of sodium bicarbonate would be needed?
we
Now that we have moles of HCl
Firstcalculate
calculate thegrams
moles ofofHCl
can
NaHCO3
0.25 mol HCl 1 mol NaHCO
needed to clean3
84.0 g of NaHCO3
up the HCl spill = 22.0 grams
of NaHCO3
1 mol NaHCO
3
1
mol
HCl
Solving for Moles of HCl, the molarity expression becomes….
0.1 M =
mol HCL___
2.5 L of solution
moles HCl = (0.1 M)(2.5 L) = 0.25 mol HCl
Summarize:
• Molarity is equal to ______
divided _____
• The more _________ a solution
is, the higher the ________
• Molarity describes the amount of
____in moles in the volume in
liters
Answer Bank
liters
concentrated
moles
Molarity(M)
volume
solute
Unit: Solutions
Topic: Factors that effect concentration
• Objectives: 3 of 3
• To learn what factors effect Molarity or
concentration
• To understand the concept of dilution and
calculations that involve dilution
Standard Solutions
• A standard solution is a solution whose
concentration is accurately known
• When the appropriate solute is available in pure
form a standard solution can be prepared by
weighing out a sample of solute transferring it
completely to volumetric flask and adding enough
solvent to bring the volume up to the mark on the
neck of the flask
What is a standard solution?
• A solution ________ is accurately known
Answer Bank
liters
concentrated
moles
Molarity(M)
volume
solute
Adding Solute:
Increases Concentration
Let’s say we have a 1M NaCl Solution
and we would like to make a 3M NaCl Solution
In order to make a stronger more
concentrated solution, we need to add
more solute in this case Salt or NaCl
3
1M
M NaCl
NaCl Solution
Solution
Evaporation:
Increases Concentration
Let’s say we have a 1M NaCl Solution
What would happen if the solution
was left outside to evaporate???
By evaporating the
solution, more solute NaCl
remains and solution
has a greater concentration
1 M NaCl Solution
3 M NaCl Solution
What are two ways to
increase Concentration or
Molarty?
• By adding more ______ or to a
solution
• Ex: I added more salt to a 1M
solution to make a 3M solution
• By letting the solution _____
Answer Bank
after
volume
concentration
solvent
before
Dilution
evaporate
solute
Dilution:
Decreases Concentration
Let’s say we have a 12M HCL
Solution and we would like to
make a 3M HCl Solution
In order to make a weaker solution
and decrease the concentration of
HCl, we need to add more water
(solvent) That is, we need to dilute it!!
3 M HCl Acid Solution
Weaker Acid
12 M HCl Acid Solution
Very Strong Acid!!!!
How do we decrease
Concentration or Molarty?
• By adding more ______ or
water to a solution
• Dilution _______ the
concentration or Molarity (M)
• Ex: I diluted the 12M solution in
order to make a 3M solution
Answer Bank
after
volume
concentration
Solvent
decreases
before
Dilution
increases
Dilution Calculations
• A typical dilution calculation involves determining
how much water must be added to an amount of
known stock solution
• The key to doing these calculations is to
remember that only water (solvent) is added to
the solution
• The amount of solute in the final more dilute
solution is the same amount of solute in the
original concentrated stock solution
• That is,
• Moles of solute after solution = Moles of solute before dilution
Dilution Equation
• Recall that a standard solution is a solution in
which the concentration is accurately known
• Chemist’s use a dilution equation to create
standard solutions
Volume
before dilution
Volume
after dilution
M1V1 = M2V2
Molarity
before dilution
Molarity
after dilution
What is the dilution equation?
•
•
•
•
M1V1 = M2V2
M1 = Molarity before______
V1 = Volume _____ dilution
M2 = Molarity ______dilution
V2 = ______after dilution
Answer Bank
after
volume
concentration
solvent
before
dilution
Demo:
•
•
•
•
I have 500ml of a 2M CuSO4 solution
I want to make a 1M solution
What will my molarity be if I add 500mL
Use your dilution equation to help me out….
Volume
before dilution
Volume
after dilution
M1V1 = M2V2
Molarity
before dilution
Molarity
after dilution
Practice:
# 6 Dilutions Worksheet
If I have 40 mL of a 12 M HCl solution, what
will the concentration be if I add 960 mL
more water to it?
Plugging in our values we get:
Volume before
dilution = 42mL
Volume after
dilution = 1000
mL
(12.0M)(42.0mL) = M2 (960+40mL)
Solving for M2 we get…..
M2 = (12.0M)(42.0mL)
1 1 (1000mL)
2 2
M2 = 0.5 M
MV = MV
If we add
more water,
theafter
molarity or
Concentration
before
Molarity
dilutionconcentration
= 12.0M
dilution
????
should=decrease
Practice:
# 7 Dilutions Worksheet
If I have 340 mL of a 0.5 M NaBr solution,
what will the concentration be if I add 560
mL more water to it?
Plugging in our values we get:
Volume after Dilution
Volume before
dilution = 340mL
(0.5M)(340mL)
== 560
M+2 340
(900mL)
= 900 mL
Solving for M2 we get…..
M2 = (0.5M)(340mL)
1 1 (900mL)
2 2
M2 = 0.19 M
MV = MV
If we add more water, the molarity or
Concentration
before
Molarity after
concentration
should
decrease
dilution = 0.5M
dilution = ????
Practice:
# 7 Dilutions Worksheet
If I have 340 mL of a 0.5 M NaBr solution,
what will the concentration be if I add 560
mL more water to it?
Plugging in our values we get:
Volume after Dilution
Volume before
dilution = 340mL
(0.5M)(340mL)
== 560
M+2 340
(900mL)
= 900 mL
Solving for M2 we get…..
M2 = (0.5M)(340mL)
1 1 (900mL)
2 2
M2 = 0.19 M
MV = MV
If we add more water, the molarity or
Concentration
before
Molarity after
concentration
should
decrease
dilution = 0.5M
dilution = ????
Summarize:
• Molarity is equal to _______ of solute divided by
Answer Bank
_________of solution
Solute(2)
• To increase molarity or concentration, we add
liters
more _______.
concentration
solvent
• To dilute a solution and decrease Molarity or
moles
Concentration, we add only more _______.
Dilution
• The amount of _______ doesn’t change.
after
• In the equation, M1 x V1 = M2 x V2, M1 is the
molarity of a solution before ______ and V2 is
the _______of a solution ______ dilution.
Dilution Solutions
• We can check our calculations from our
previous problem using the dilution
equation M1 = 17.5 M
V1 = ????
M2 = 1.0 M
V2 = 2.0 L
(17.5M)(V1) = (1.0M)(2.0)
V1 = (1.0M)(2.0)
17.5M
V1 = 0.11L
Dilution Calculations
• The number of moles of solute stays the
same but more water is added increasing
the volume, so the molarity(M) decreases
• Let’s review our definition of molarity:
What happens when add more water?
• Molarity (M) = moles of solute
liters of solution
Molarity
Decreases
Volume Increases
Moles remain
constant
Dilution Calculations
• For example, suppose we want to prepare 2.0L of a1M
acetic acid (vinegar) from a 17.5 M stock solution of
acetic acid. What volume of stock solution is required?
We have a 17.5M
of a stock solution of
acetic acid available
17.5 M
Acetic Acid
We need to
prepare a 2.0L 1M
acetic acid solution
1.5L
Dilution Calculations
• To solve the problem, we need to determine
the number of moles of acetic acid (solute)
needed in the final solution:
2.0L solution
1 mol HC2H3O2
= 2.0 mol HC2H3O2
1L HC2H3O2
• Now we need to find the volume of our 17.5 M
solution (stock solution) that contains 2.0 mol
of HC2H3O2
Dilution Calculations
• Remember:
• Molarity = moles of solute
liters of solution
• Solving for Liters (V), the expression becomes……
moles of solute
• V=
Molarity
2.0 mol HC2H3O2
• V=
17.5 mol/L
= 0.11 L of solution
• Therefore to make 2.0L of a 1 M acetic solution
we take 0.11 Liters of our 17.5M stock solution
of acetic acid and dilute it to a total volume of 0.5
liters
First we add
0.11 liters of our
stock 17.5 solution
Then we add
2.0 liters of water
The resulting
Solution is 1M
Acetic acid
Dilution Calculations
• Moles of solute = (Molarity)(Liters of solution)
• We do this because the moles of solute in the
stock solution = moles of solute in our new
solution were trying to make
0.5L solution
1 mol HC2H3O2
= 0.5 mol HC2H3O2
1L HC2H3O2
Visulaize:
1 mol NaOH
= 0.288 mol NaOH
40.0 g NaOH
Solubility
• What happens when you put a salt in
water?
• Why does the salt disappear?
• What is really happening when something
dissolves?
• Earlier, we saw that when sodium chloride
dissolves in water, the resulting solution
conducts electricity
Unsaturated Solutions
• A solution that has not reached the limit of
solute that will dissolve in it is said to be
“Unsaturated”
• In other words, it is a solution that is able
to dissolve more solute at that
temperature
• If we were to add more solute (salt), it would
continue to dissolve because the solution is
unsaturated
What is a Unsaturated Solution?
• A solution that is able to
____more solute at that_______
Answer Bank
Largest
concentration
dissolve(s)
Homogeneous
Lesser
Polar
Higher
Surface
Crystal
Temperature
Two
Saturated Solutions
• If you were to keep adding salt to water,
eventually it would stop dissolving
• There is a limit to how much solute can be
dissolved in a solvent (water)
• When a solution can no longer dissolve
the solute, we say the solution is
“saturated”
• That is, the solute (salt) will no longer
dissolve at a certain temperature
What is a Saturated Solution?
• A solution in which the solvent
can ____no more of a specific
solute at a particular _______
Answer Bank
Largest
concentration
dissolve(s)
Homogeneous
Lesser
Polar
Higher
Surface
Crystal
Temperature
Two
Supersaturated Solutions
• Sometimes when a solid is
dissolved to the saturation level
at an elevated temperature and
then allowed to cool, all of the
solid may remain dissolved
• This type of solution is called a
supersaturated solution
• It contains more dissolved solid
than a saturated solution will
hold at that temperature
• A supersaturated solution is very
unstable, adding a crystal of the
solid will cause immediate
precipitation of a solid
What is a Supersaturated Solution?
• A supersaturated solution
has a _________of solute
that is _____than its
solubility. A _____solute
added to a supersaturated
solution causes the
remaining solute to
precipitate out
Answer Bank
Largest
concentration
dissolve(s)
Homogeneous
Lesser
Polar
Higher
Surface
Crystal
Temperature
Two
Factors Affecting the Rate of
Dissolution
• What do you think effects how fast salt will
dissolve in water?
• 3 things to consider is surface area,
stirring, and temperature
Factors Affecting the Rate of
Dissolution
• When considering surface are,
smaller salt crystals will
dissolve faster than larger salt
crystals
• Temperature causes the
molecules to move faster
increasing te rate of dissolution
• Finally, stirring removes newly
dissolved particles from the
solid surface and continuously
exposes the surface to fresh
solvent (water molecules)
What factors affect the rate of
dissolution?
Answer Bank
• 3 things:
– _____ area
– stirring, and
– __________
Largest
concentration
dissolve(s)
Homogeneous
Lesser
Polar
Higher
Surface
Crystal
Temperature
Two