1. Solutions and Solubility
Unit 4
Solutions
and
Solubility

2. Solutions A solution is a homogenous mixture of 2 or more substances
Homogenous has uniform composition (like salt water in the ocean)
Solutions are clear and transparent
ex: Salt Water Oil Water
oil
Cl-
Na+
Na+
Cl-
water
Na+
Cl-

3. Definitions:
1) Solvent is the substance present in the largest quantity.
ex: Water is the universal solvent
2) Solute is the substance present in the smallest quantity
ex: Salt Water – Salt is the solute, water is the solvent
3) Dilute is when there is a small amount of solute with respect to a large amount of solvent.
4) Concentrated is when there is a large amount of solute with respect to a small amount of solvent

4. 5) Aqueous Solutions are solutions in which the solvent is water
6) Tincture is a solution in which alcohol is the solvent
7) Alloy is a solid solution of two or more metals
8) Amalgam is an alloy where one of the metals is mercury.

5. Why are Solutions Important?
Many medicines are taken as solutions like cough syrups and antacids
2/3 of our body is a water solution
Hormones, nutrients and gases are transported throughout the human body and are dissolved in the blood stream
There are 9 different types of solutions:

6. Ethylene glycol in water
Solvent
Solute
Examples
Uses
Liquid
Ethylene glycol in water
Antifreeze
Solid
NH4NO3 in water
Ice Pack
Gas
CO2 in water
Carbonated Drinks
Napthalene in O2
Moth Balls
Gasoline in O2
Engine combustion
He and O2
Deep Sea Diving
Cu and Au
Solder
H2 in Palladium
Gas Stove Lighter
Hg and Dental alloy
Dental Fillings

7. Concentration This refers to the amount of solute per unit volume
The formula is: C = n/v and the units are mol/litre (M)

8. ex: An antacid solution may be prepared by dissolving 15g of sodium bicarbonate (baking soda) in enough water to make a 250ml solution. What is the molar concentration?
Step 1: Change grams to moles
15g NaHCO3 =
0.179 mol
84.01
Step 2: Change ml to litres
250ml =
0.25 L
1000
Step 3: Use new formula to solve for C
C = n/v =
(0.179mol) / (0.25L) =
0.716 M

9. Saturated, Unsaturated and Supersaturated
Unsaturated Solutions contain less solute than it can hold at its’ maximum. (kind of like dilute)
Saturated Solutions contain the exact maximum amount of solute (like the perfect glass of Iced Tea)
Supersaturated Solutions contain more than the maximum amount of solute. This is done by making a saturated solution at high temperatures and then cooling it gradually. There are only two solutions that you need to know that do this: NaCH3COO and Na2S2O3

10. Diluting Solutions
These problems involve lots of solvent and a little amount of solute
There will be an initial concentration and volume as well as a final concentration and volume
The formula is:
CiVi = CfVf
i = initial
f = final

11. ex: Prepare a 1. 00L solution of 5. 0M HCl
ex: Prepare a 1.00L solution of 5.0M HCl. The original concentration is 12.4M HCl.
Ci =
Vi =
Cf =
Vf =
12.4 M ? 5M 1L
CiVi = CfVf
(12.4)(x) = (5)(1)
12.4
12.4
x = 0.403L
But, we need to make a 1L solution so this answer tells us we need 403ml of HCl and 597ml of H2O

12. The final concentration is 0.636M
A concentrated (19.1M) sodium hydroxide solution was diluted. What concentration is made if 10L of the concentrated sol’n was diluted to 300L?
Ci =
Vi =
Cf =
Vf =
19.1M
10 L ?
300 L
CiVi = CfVf
(19.1)(10) = (x)(300)
300
300
0.636 M = x
The final concentration is 0.636M

13. Ionic Concentrations in Electrolytic Solutions
When an ionic compound is dissolved in water, it dissociates into its’ ions
These ions conduct an electric current and is therefore called an electrolytic solution
We would write the equations as decomposition reactions
We can determine the concentrations of the ions using Concentration-Concentrations (which are the same as mol-mol).

14. Steps:
1) Write a balanced dissociation equation
2) Do a mol-mol
ex: If we have 0.23M Al2(SO4)3 what is the concentration of each ion?
Al2(SO4)3
2Al SO42-
2 Al3+
0.23M Al2(SO4)3 x
= M Al3+
1 Al2(SO4)3
3 SO42-
0.23M Al2(SO4)3 x
= 0.69M SO42-
1 Al2(SO4)3

15. Solution Stoichiometry
This type of stoichiometry involves single replacement reactions
Steps:
1) Write a balanced equation
2) Do a mol-mol with the concentration

16. ex:If 200ml of 0.100M AgNO3 completely reacts with copper, what mass of Ag(s) will be produced?
Cu(NO3)2(aq)+ 2Ag(s)
2AgNO3(aq) + Cu(s)
__2Ag__
0.100M AgNO3 x
= 0.1M Ag
2AgNO3
n = (C)(v) =
(0.1M)(.2L) =
0.02 mol Ag
m = (n)(MM) =
(0.02mol)(107.82g/mol)
= g Ag

17. Precipitation Stoichiometry
Precipitates are solid substances formed from reactions in solution
These are all double replacement reactions
Steps:
1) Write a balanced equation
2) Do a mol-mol
3) Find the mass of the precipitate (if asked)

18. ex: What mass of precipitate will be produced when 100ml of 2
ex: What mass of precipitate will be produced when 100ml of 2.0M BaCl2 solution is mixed with Na2SO4 solution?
BaCl2(aq) + Na2SO4(aq)
BaSO4(s)+ NaCl(aq) 2
1 BaSO4
2.0M BaCl2 x
= 2.0M BaSO4
1 BaCl2
n = (C)(v) =
(2.0M)(.1L) =
0.2mol BaSO4
(0.2mol)(233.39g/mol)
m= (n)(MM) =
= g BaSO4

19. Solubility
Solubility describes how much solute can be dissolved in a solvent at a particular temperature to make a saturated solution
This means that even if there were more solute available, no more would dissolve
The amount that will dissolve is based on the compound’s intermolecular forces
We know that ionic solids have high intermolecular forces whereas covalent solids have relatively weak forces

20. Therefore, the electronegativity of a covalent compound must be discussed
Electronegativity is a measure of the attraction of an atom for electrons in the covalent bond
We can place covalent compounds into two categories of electronegativity:
1) Polar Molecules: occur when two different atoms form a molecule
- the molecule will have 2 polar ends (a positive and a negative end)

21. The poles are called dipoles which are the relative (imaginary) charge on the atoms.
Polar solvent can dissolve other polar molecules and ionic solutes δ- O δ+ δ+ H H
δ+ = positive dipole
δ- = negative dipole

22. 2) Non-Polar Molecules: occur when two of the same molecules combine with equal distances between their nuclei
- all diatomic molecules fit into this category
- non-polars can only separate molecules of other non-polar molecules
• •
• • Cl Cl = Cl Cl
• • • •
• •
• •
• •

23. Rules of Solubility
Since dissolving is an endothermic process, the following rules must be observed:
1) solids have high solubility at high temperatures
2) gases have high solubility at low tempertures
3) gases have high solubility at high pressures
4) some liquids like mineral oil do not mix with water. They are immiscible and form a separate layer
5) some liquids like methanol can dissolve in water with no maximum amount. They are miscible with water

24. Solubility Curves
A solubility curve shows how much solute will dissolve in water over a range of temperatures.
Each curve is either a gas or a solid (no liquids)
Solid curves sweep up to the right
Gas curves sweep down to the right
A flat curve shows that the solubility of that substance is not really affected by changes in temperature.

26. The lines represent a saturated solution
Any point under the line is unsaturated
100g H2O = 100ml H2O = 100cm3 H2O
To find the mass of solute at a given temperature, draw a line up to the saturated solution line.
ex: How many grams of KNO3 can be dissolved at 50ºC?
80g of KNO3 solute

27. We need 60g to be saturated but we only have 45g
ex 2: How many grams of solute (KClO3) can be dissolved in 200g of water at 80°C?
In 100g H2O = 40g KClO3
In 200g H2O = 80g KClO3
ex 3: We have 45g NH4Cl at 70°C in 100g H2O. Is this a saturated solution? If not, how much more solute must be added?
It is Unsaturated!
We need 60g to be saturated but we only have 45g
Therefore, we need an extra 15g NH4Cl