Arnoldi
Honors Chemistry
Solubility Part Two
Note Packet
I. Solubility Curves and Tables
A. Comparison
Solubility Term / Amount that Dissolves per 100 grams of Water / Connection to EquilibriumSoluble /
get to equilibrium.
Slightly Soluble / Gets to equilibrium .
Insoluble / Gets to equilibrium .
NOTE: Why do slightly soluble and insoluble solutes reach solubility equilibrium very easily?
The little bit that can dissolve does, then no more can dissolve unless ______.
So, how does it look in an equation?
for soluble for insoluble / slightly soluble
NOTE: The term “insoluble” is actually not accurate for ionic substances dissolved in water. NO ionic substances are completely insoluble in water.
So, what is the more appropriate term? ______
NOTE: What are the other terms on the solubility chart?
D = ______
NI – ______
B. Important Definitions
1. ______the solution contains the maximum amount of solute
for that amount of solvent at those conditions
(always temperature, for gases pressure, too)
2. ______the solution contains less than the maximum amount of solute for that amount of solvent at those conditions
3. ______the solution contains more than the maximum amount of solute for that amount of solvent at those RARE! conditions
How is this possible? These solutions are created by saturating a hot solution and allowing it to cool undisturbed.
4. ______the maximum amount of solute is dissolved, & more solute remains as undissolved crystals
5. Concentrated a ______/ solvent is dissolved
6. Dilute a ______/ solvent is dissolved
COMPLETE PROMPT ONE NOW
B. Reading the Curve
1. Endothermic vs. Exothermic (Heat of Solution)
Curving ______is endothermic (higher heat, ______dissolves)
Examples:
Curving ______is exothermic (more heat, ______dissolves)
Examples:
2. At __ ‘C, how much will it hold?
a. Straightforward Example
At 20’C, how much KNO3 will dissolve in 100g water? 32g
b. Mathematic Example
At 50’C, how much NaCl will dissolve in 75g of water? 38, 28.5
3. Given ___ g, at what temperature will it be saturated?
a. Straightforward
At what temperature will 100 g of sodium nitrate, in
100 g of water form a saturated solution? 34’C
b. Mathematics
At what temperature is 85g of NH4Cl in 150 g of water
saturated? 57g, 65’C
COMPLETE PROMPT TWO NOW
4. What is its condition?
Exactly Saturated
(not common) / Have __ Allowed / No value to Find / Yes
Saturated with Undissolved Salt / Have __ Allowed / Yes
Supersaturated (never unless specifically told the extra amount IS dissolved) / Have __ Allowed
(and it IS dissolved) / No value to Find / Yes, (but the equilibrium is easily disturbed which would result in a rapid recrystallization).
Unsaturated (more can dissolve) / Have __ Allowed / No
NOTES: Where does “have” come from? It is ______in the problem.
Where does “allowed” come from? It is found ______.
If the “have” value is not in 100 grams of solvent, what happens?
You must first find the “allowed” value on the chart, then convert it to the actual “have” amount of solvent. Always convert ______to ______!
a. Straightforward Examples
Example: Describe a solution containing 45 g of NaCl
in 100 g of water at 80’C. a(39), sat 6g
c. Mathematics
Now, compare ___ and ___.
Example: Describe a solution containing 40 g of KNO3
in 80 g of water at 50’C. a 78 à 62.4, 22ud
COMPLETE PROMPT THREE NOW
II. Concentration of Solutions
a ______of the amount of solute / solvent
A. Molarity, M
1. Equation
*because the solute particles (usually) fit between the solvent particles, this is the same as Liters of Solvent
2. Example
a. Easy What is the molarity of a solution if 1.50 moles of KCl dissolve in 750 mL of water? (2.0 M)
b. With grams, solve for L How much water is required to make a 2.00 M solution containing 40.5 g of NaCl?
.692 mol, .346 L)
OTHER IMPORTANT TYPE: solve for grams ….
Must solve for moles first, then convert to grams.
B. Molality, m
1. Equation
2. Examples: Any Example Just Like Molarity
Remember: For Water, because 1.00g = 1.00 mL, kilograms and liters are interchangeable!
COMPLETE PROMPT FOUR NOW
C. Percent Solution
1. Equations (in general, solute/solution X 100)
2. Example
a. Easy What is the percent by mass of a solution containing 10.5 g KCl in 1500 mL of water? .70%
b. Solve for Solute How much Copper (II) Nitrate is required to make a 20.0% solution in 650. mL of water? 162.5g (no sf)
c. What if we don’t directly give masses? i.e. What if we gave volumes and densities?
D. Dilution Formula (for any concentration unit)
Important Note (from book): diluting a solution ______the number of moles of solute ______, but the ______of moles of solute in solution ______!
So, if we take a certain amount of solute in a certain amount of solvent (Co, Vo), and we add water to get to a new volume (Vn) we can figure
out Cn (clearly it went down… volume and concentration are ______proportional).
Alternatively speaking, if we know what volume we want to get to, (Vn), and we know what concentration we want to get to, (Cn), and we know the concentration of our current solution, (Co), we can figure out how much of that (Vo) we need to add to water to get the desired concentration.
C = o =
V = n =
Example: How many ml of a solution containing 11.70 grams of NaCl in 200.0 ml of solution would be needed to prepare 500.0 ml of a 0.0500 M solution?
OK. Let’s do this the long way first.
First, calculate the molarity of the original solution:
(convert 11.70 g NaCl to moles).
11.70 g NaCl x 1 mole NaCl =
58.0 g NaCl
M = .2000 moles = 1.000 M
.2000 L
So, I have 200.0 mL of a 1.000M solution.
Now, I want 500.0 mL of a 0.0500M solution. How many moles is this?
M = mol
L
(M) (L) = mol = (0.0500 mol) ( 0.500 L) = 0.250 moles
L
So, I need 0.0250 moles.
Now, what volume of the first solution gives me that amount of moles?
M = mol L = mol = 0.0250 moles = .0250 L = 25.0 mL needed
L M 1.00 mol/L
Now, let’s use the dilution formula to calculate the ml of NaCl solution needed.
In other words, how much of the first solution do I need to make the second
solution? The rest of the volume will simply be water. 25.0 mL of NaCl solution needed
How’d we do that? ______need to be consistent.
(each equation) Mold = moles old Mnew = molesnew
liters old litersnew
(rearrange) (Mold )(liters old) = moles old (Mnew)(liters new) = moles new
moles are equal, so…
III. Colligative Properties
A. Definitions
1. ______properties that depend on the amount of
solute present, and the nature of the solvent
that it is dissolved in
Special Notes:
If a solution conducts electricity it is an electrolyte. If it was an ionic solute that was dissolved, freeing ions to conduct the electricity, it is called ______. If it is a covalent compound that dissolved, making ions to conduct electricity, we call this ______.
Dissociation Examples
NaCl(s) + H2O(l) yields Na+(aq) + Cl-(aq)
MgCl2(s) + H2O(l) yields Mg+2(aq) + 2Cl-(aq)
Na+1 and Mg+2 ions were originally ______to Cl-1 ions.
After dissolving, both ions are ______.
They started as ions (together) and ended as ions (apart).
They are/were always ______!
Ionization Examples
HCl(g) + H2O(l) yields H+(aq) + Cl-(aq)
H2SO4(l) + H2O(l) yields 2H+(aq) + SO4-2(aq)
H ______were attached to Cl ______. When they are hydrated by the water, the H atoms ______their electron pair and become ______, and the Cl atoms ______their own electron and the H electron from the shared pair to become ______. So, we ______have ions that are freely roaming around and conducting electricity.
They started as ______(together), they end as ______(apart).
Ions ______!
In both cases, if lots of ions are made (it completely ionizes or dissociates) it is a ______electrolyte. If only a few ions are made (it partially ionizes or dissociates), it is a ______electrolyte.
Also, Substances that are not acids, bases, and salts do not dissociate/ionize. Substances that dissolve, but don’t make ions, and therefore do not conduct electricity, are called ______.
COMPLETE PROMPT FIVE NOW
2. ______when a solute is dissolved in a solvent, the original freezing point of the solvent will go down
Why do we salt the roads? So the snow/freezing rain will
no longer be able to freeze at
32’F / 0’C.
Why does freezing point depression occur?
O Cl- O
H H ………….. O ………… H H
H H
Na+
The solute (NaCl) ______. (ex: antifreeze)
3. ______when a solute is dissolved in a solvent, the
original boiling point of the solvent will go up
Why do we add salt to the pot when cooking pasta?
The water will now boil at a higher temperature, thus the pasta will cook faster.
Why does boiling point elevation occur?
The solute takes up space on the ______of a liquid. This decreases the ability of the liquid to ______. Thus, the vapor pressure ______. Boiling occurs when the atmospheric pressure ______the vapor pressure. So, an ______in energy is needed to increase the vapor pressure to reach the atmospheric pressure.
(continued next page)
= solvent
versus
= solute
“A” “B”
Which would produce more (water) vapor?
Which would have a higher vapor pressure?
Which would take less energy to raise the vapor pressure to atmospheric pressure?
Which would have a higher boiling point?
B. Factors that Affect Freezing Point Depression / Boiling Point Elevation
1. ______is a constant… would be found on a table
2. [Solute]
Important Note:
Concentration is dependent on how “things” dissolve.
For example, ionic compounds break into ions, so if AX has a concentration of 1 M, then when it breaks down there are ___ of A+ions, and ___ of X- ions thus a total ion concentration of ___.
for freezing point / boiling point questions, we will need concentration in molality…
a. Counting Moles of Ions Only
If 1.5 moles of MgCl2 dissolve in water, how many moles of each ion are present?
b. Determining Concentration of Ions Only
If 0.200 moles of AlCl3 dissolve in 4.0 L of water, what is the concentration in molarity of aluminum ions? chlorine ions?
0.050 M Al+3 0.15 M Cl-1
REMEMBER:
then…
ANOTHER WAY:
SHORT CUT to BOTH WAYS
3. Equations
T =
f = (down)
b = (up)
Kf, Kb = constants (depend upon the solvent)
page 494, 495
m = ______=
*If ionic, this is the total number of ions!
*Total Ion Moles = (moles of substance) ( total number of ions)
4. Examples of Colligative Property (FPD or BPE) Problems
What is the change in the boiling point of benzene if 1.5 moles
of a nonpolar solute dissolve into 650 g of benzene?
Kb = 2.53 ‘C / molal
NOTES: (1) This means that the new boiling point of Benzene
is 5.83’C higher than it originally was.
(2) Molal (m) was straight-forward because it was a
nonpolar substance that did not break into ions.
What is the new freezing point if 2.0 moles of sodium
chloride dissolve in 1.0 kg of water? Kf = -1.86’C / molal.
Be aware, we could also go backwards… were you given Tnew or T? Was it ionic or not?
ONE LAST THING…NIB Ion Pairing
When experiments are done regarding freezing point depression and boiling point elevation, the actual answers are different than the theoretical answers (surprise, surprise!).
Example: a solution of NaCl in water:
Concentration (molality) / Actual change in the freezing point / Theoretical change in the freezing point / % dissociation.1 / - 0.346 / - 0.372 / 93 %
.01 / - 0.0361 / - 0.0372 / 97 %
.001 / - 0.00366 / - 0.00372 / 98 %
.0001 / - 0.000372 / - 0.000372 / 100 %
Sodium Chloride can dissociate at a rate of 100% if the concentration of the solution is very low. With increased concentration, ions may come in contact with each other and rejoin resulting in less than 100% dissociation. Only at low, low concentrations do solutions have their “x” factor approach the theoretical value.
Theoretical: Actual:
X = 14 ions X = 10 “ions”
COMPLETE PROMPT SIX NOW