1. Chapter 4, Part II: Solution Chemistry

2. Properties of Solutions
Solvent
This is the liquid that is doing the dissolving
Solute
This is what is being dissolved
Form a homogenous mixture

3. Saturated vs. Unsaturated Solutions

4. Solubility
Two liquids that dissolve in each other are said to be miscible
Immiscible liquids are insoluble in each other
Think of some examples!

5. Immiscible vs. Miscible Solutions

6. Factors Affecting Solubility
Solubility increases with the increase in temperature (Easier to dissolve something when the temperature is increased)
Few exceptions that occur in the reverse

7. Concentrations of Solutions
Molarity is the concentration of moles per liters
Molarity (M) = moles of solute / liters of solution
Dilute solution contains a low concentration of solute
Concentrated solution contains a high concentration of solute

8. Practice Problems:
Calculate the molarity of a solution which contains 0.40 mol of C6H12O6 dissolved in 1.6 L of a solution.
What is the molarity of a solution containing 325 g of NaCl dissolved in 750. mL of solution?(1000 ml = 1L)

9. Solutions
stoichiometry

10. Stoichiometry overview
Recall that in stoichiometry the mole ratio provides a necessary conversion factor:
grams (x)  moles (x)  moles (y)  grams (y)
molar mass of x
molar mass of y
mole ratio from balanced equation
We can do something similar with solutions:
volume (x)  moles (x)  moles (y)  volume (y)
mol/L of x
mol/L of y
mole ratio from balanced equation

11. Practice Problems
1. If I combined 15.0 grams of calcium hydroxide with L of M HCl, how many grams of calcium chloride would be formed?
2. If ml of a M solution of lead(II) acetate is added to mL of a M solution of sodium sulfide, what mass of solid lead sulfide will be formed?

12. What Happens When a Solute Dissolves?
there are attractive forces between the solute particles holding them together; likewise for the solvent
Upon mixing the solute with the solvent, there are attractive forces between the solute particles and the solvent molecules
if the attractions between solute and solvent are strong enough, the solute will dissolve

13. Table Salt Dissolving in Water
Each ion is attracted to the surrounding water molecules and pulled off and away from the crystal
When it enters the solution, the ion is surrounded by water molecules, insulating it from other ions
The result is a solution with free moving charged particles able to conduct electricity
Tro, Chemistry: A Molecular Approach

14. Electrolytes and Nonelectrolytes
materials that dissolve in water to form a solution that will conduct electricity are called electrolytes
materials that dissolve in water to form a solution that will not conduct electricity are called nonelectrolytes
Tro, Chemistry: A Molecular Approach

15. Molecular View of Electrolytes and Nonelectrolytes
in order to conduct electricity, a material must have charged particles that are able to flow
electrolyte solutions all contain ions dissolved in the water
ionic compounds are electrolytes because they all dissociate into their ions when they dissolve
nonelectrolyte solutions contain whole molecules dissolved in the water
generally, molecular compounds do not ionize when they dissolve in water
the notable exception being molecular acids
Tro, Chemistry: A Molecular Approach

16. Salt vs. Sugar Dissolved in Water
molecular compounds do not dissociate when they dissolve
ionic compounds dissociate into ions when they dissolve
Tro, Chemistry: A Molecular Approach

17. Acids
acids are molecular compounds that ionize when they dissolve in water
the molecules are pulled apart by their attraction for the water
when acids ionize, they form H+ cations and anions
the percentage of molecules that ionize varies from one acid to another
acids that ionize virtually 100% are called strong acids
HCl(aq)  H+(aq) + Cl-(aq)
acids that only ionize a small percentage are called weak acids
HF(aq)  H+(aq) + F-(aq)
Tro, Chemistry: A Molecular Approach

18. Strong and Weak Electrolytes
strong electrolytes are materials that dissolve completely as ions
ionic compounds and strong acids
their solutions conduct electricity well
weak electrolytes are materials that dissolve mostly as molecules, but partially as ions
weak acids
their solutions conduct electricity, but not well
when compounds containing a polyatomic ion dissolve, the polyatomic ion stays together
Na2SO4(aq)  2 Na+(aq) + SO42-(aq)
HC2H3O2(aq)  H+(aq) + C2H3O2-(aq)
Tro, Chemistry: A Molecular Approach

19. Classes of Dissolved Materials
Tro, Chemistry: A Molecular Approach

20. Acid-Base Reactions
also called neutralization reactions because the acid and base neutralize each other’s properties
2 HNO3(aq) + Ca(OH)2(aq)  Ca(NO3)2(aq) + 2 H2O(l)
the net ionic equation for an acid-base reaction is
H+(aq) + OH(aq)  H2O(l)
as long as the salt that forms is soluble in water
Tro, Chemistry: A Molecular Approach

21. Acids and Bases in Solution
acids ionize in water to form H+ ions
more precisely, the H from the acid molecule is donated to a water molecule to form hydronium ion, H3O+
most chemists use H+ and H3O+ interchangeably
bases dissociate in water to form OH ions
bases, like NH3, that do not contain OH ions, produce OH by pulling H off water molecules
in the reaction of an acid with a base, the H+ from the acid combines with the OH from the base to make water
the cation from the base combines with the anion from the acid to make the salt
acid + base salt + water
Tro, Chemistry: A Molecular Approach

22. Practice
Write the balanced molecular and net ionic equations for the reaction between:
1. Hydrobromic Acid and Potassium Hydroxide
2. Nitric Acid and Calcium Hydroxide
****Hint: Remember what an acid-base reaction always produces!

23. Electrolytes Strong Acids and Strong Bases= Strong Electrolytes
Weak Acids and Weak Bases = Weak Electrolytes

24. Red-ox Reactions
other kinds of reactions involve transferring electrons from one atom to another – these are called oxidation-reduction reactions
also known as redox reactions
many involve the reaction of a substance with O2(g)
4 Fe(s) + 3 O2(g)  2 Fe2O3(s)
Tro, Chemistry: A Molecular Approach

25. Oxidation and Reduction
atoms that lose electrons are being oxidized, atoms that gain electrons are being reduced
Leo
Ger
2 Na(s) + Cl2(g) → 2 Na+Cl–(s)
2Na → 2Na+ + 2e– oxidation
Cl2 + 2 e– → 2 Cl– reduction
Tro, Chemistry: A Molecular Approach

26. Electron Bookkeeping
for reactions that are not metal + nonmetal, or do not involve O2, we need a method for determining how the electrons are transferred
chemists assign a number to each element in a reaction called an oxidation state that allows them to determine the electron flow in the reaction
even though they look like them, oxidation states are not ion charges!
oxidation states are imaginary charges assigned based on a set of rules
ion charges are real, measurable charges
Tro, Chemistry: A Molecular Approach

27. Rules for Assigning Oxidation States
rules are in order of priority
free elements have an oxidation state = 0
Na = 0 and Cl2 = 0 in 2 Na(s) + Cl2(g)
monatomic ions have an oxidation state equal to their charge
Na = +1 and Cl = -1 in NaCl
(a) the sum of the oxidation states of all the atoms in a compound is 0
Na = +1 and Cl = -1 in NaCl, (+1) + (-1) = 0
Tro, Chemistry: A Molecular Approach

28. Rules for Assigning Oxidation States
(b) the sum of the oxidation states of all the atoms in a polyatomic ion equals the charge on the ion
N = +5 and O = -2 in NO3–, (+5) + 3(-2) = -1
(a) Group I metals have an oxidation state of +1 in all their compounds
Na = +1 in NaCl
(b) Group II metals have an oxidation state of +2 in all their compounds
Mg = +2 in MgCl2
Tro, Chemistry: A Molecular Approach

29. Rules for Assigning Oxidation States
in their compounds, nonmetals have oxidation states according to the table below
nonmetals higher on the table take priority
Nonmetal
Oxidation State
Example F -1
CF4 H +1
CH4 O -2
CO2
Group 7A
CCl4
Group 6A
CS2
Group 5A -3
NH3
Tro, Chemistry: A Molecular Approach

30. Practice – Assign an Oxidation State to Each Element in the following
Br2 K+
LiF
CO2
SO42-
Na2O2
Tro, Chemistry: A Molecular Approach

31. Practice – Assign an Oxidation State to Each Element in the following
Br2 Br = 0, (Rule 1)
K+ K = +1, (Rule 2)
LiF Li = +1, (Rule 4a) & F = -1, (Rule 5)
CO2 O = -2, (Rule 5) & C = +4, (Rule 3a)
SO42- O = -2, (Rule 5) & S = +6, (Rule 3b)
Na2O2 Na = +1, (Rule 4a) & O = -1, (Rule 3a)
Tro, Chemistry: A Molecular Approach

32. Oxidation and Reduction Another Definition
oxidation occurs when an atom’s oxidation state increases during a reaction
reduction occurs when an atom’s oxidation state decreases during a reaction
CH O2 → CO2 + 2 H2O –
oxidation
reduction
Tro, Chemistry: A Molecular Approach

33. Oxidation–Reduction oxidation and reduction must occur simultaneously
if an atom loses electrons another atom must take them
the reactant that reduces an element in another reactant is called the reducing agent
the reducing agent contains the element that is oxidized
the reactant that oxidizes an element in another reactant is called the oxidizing agent
the oxidizing agent contains the element that is reduced
2 Na(s) + Cl2(g) → 2 Na+Cl–(s)
Na is oxidized, Cl is reduced
Na is the reducing agent, Cl2 is the oxidizing agent
Tro, Chemistry: A Molecular Approach

34. Identify the Oxidizing and Reducing Agents in Each of the Following
3 H2S + 2 NO3– H+ ® 3 S + 2 NO + 4 H2O
MnO2 + 4 HBr ® MnBr2 + Br2 + 2 H2O
Tro, Chemistry: A Molecular Approach