Announcements
• Print worksheet #5 prior to your Thursday
discussion section
• A full schedule of readings and suggested
problems is posted on the course website
• LON-CAPA assignment 3 is due Friday at 9am
• Don’t forget to bring your Clicker to class
EVERY day
The points from last week have been uploaded to
the online gradebook. Check to make sure your
points are shown!
Classification of Matter
matter – anything that occupies space and has mass
matter exists in three states:
solid
fixed volume and shape
liquid
fixed volume but assumes shape of container
gas
assumes volume and shape of container
pure substances have a constant composition; these are either
compounds or free elements
examples: water, methane, sodium chloride, sodium
mixtures are combinations of pure substances
Mixtures
homogeneous mixtures (aka solutions) contain visibly
indistinguishable parts
examples: air, brass (copper + zinc), hot tea
heterogeneous mixtures contain visibly distinguishable parts
examples: oil and vinegar, dinner salad
from “Chemistry” by Julia Burdge
Solution Chemistry
In a solution containing two or more components…
solvent = substance present in major amount
solute = substance(s) present in minor amount
Solution
Phase
Solvent
Solute
air
gas
N2
O2, Ar,
CO2, etc
steel
solid
Fe
C
tap
water
liquid
H2O
salts
Solution Chemistry
Which of the following entries correctly describes a glass of iced tea?
Type of Solution
Solvent
Solute
A
heterogeneous
tea
ice
B
heterogeneous
ice
tea
C
homogeneous
tea
ice
D
homogeneous
ice
tea
Water is a Polar Solvent
Bonds in a water molecule are formed when electrons are shared
between the hydrogen and oxygen atoms
• oxygen and hydrogen do not share electrons equally
• electrons, on average, spend more time near the oxygen
• oxygen develops a partial negative charge (indicated by δ-) while
hydrogen develops a partial positive charge (indicated by δ+)
δ+
• this separation of charges is called a dipole
• a molecule with a permanent dipole is
defined as a polar molecule
δ+
δ-
Water is a Polar Solvent
“Like dissolves like”
Polar solutes (ex. NaCl, ethanol) can dissolve in water
Nonpolar solutes (ex. octane, fat) will not dissolve in water
Electrolyte – a substance that when dissolved in water produces a
solution that can conduct electricity
strong – dissociate completely into separate ions
weak – only dissociates partially to produce ions; solution
contains many undissociated molecules
non – dissolve in water but do not produce ions
Electrolytes
non (no ions)
from “Chemistry” by Julia Burdge
weak (some ions)
strong (many ions)
see Figure 4.4
Acids
acid – a molecule in which H+ ions are attached to an anion
anions without oxygen: named as “hydro_______ic acid”
HCl
anion = chloride
acid = hydrochloric acid
HBr
anion = bromide
acid = hydrobromic acid
HCN anion = cyanide
acid = hydrocyanic acid
anions with oxygen have their own naming conventions
anion ending in “ate” Æ “__________ic acid”
ex. H2SO4
anion = sulfate
acid = sulfuric acid
anion ending in “ite” Æ “___________ous acid”
ex. H2SO3
anion = sulfite
acid = sulfurous acid
Electrolytes
Rule
Exceptions
1. Most acids are weak electrolytes
strong
acids
2. Most bases are weak electrolytes
strong
bases
3. Most salts are strong electrolytes
HCl, HBr, HI, HNO3,
H2SO4, HClO4 and
HClO3
LiOH – CsOH and
Ca(OH)2 – Ba(OH)2
HgCl2 and Hg(CN)2
Strong Electrolytes
dissociate completely to form hydrated ions
strong acids
HCl (g)
→ H+ (aq)
+ H2O (l)
+ Cl- (aq)
→
strong bases
NaOH (s) + H2O (l)
→ Na+ (aq) + OH- (aq)
salts
MgSO4 (s) + H2O (l)
→ Mg2+(aq) + SO42-(aq)
Weak Electrolytes
do not dissociate completely
weak acids
HF (g)
+ H2O (l)
at equilibrium all species are
present
' H+ (aq)
+ F- (aq)
→
weak bases
NH3 (g)
+ H2O (l)
' NH4+ (aq)
+ OH- (aq)
' Hg2+ (aq)
+ 2Cl- (aq)
weak electrolytic salts
HgCl2 (s)
+ H2O (l)
Non- Electrolytes
do not dissociate to form ions
CH3CH2OH (l)
+ H2O
→ CH3CH2OH (aq)
→
another common non-electrolyte is table sugar (sucrose)
which has the formula C12H22O11
Properties of aqueous solutions
ionic
covalent
NaCl
C6H12O6
do not conduct electricity
conduct electricity
electrolytes produce ions
non-electrolytes
salts produce other anions and cations
bases produce OH- in aqueous solutions
acids produce H+ in aqueous solutions
Solution Composition
concentration is the amount of chemical present in a solution
molarity is one of the most common expressions of concentration
molarity = M = amount of solute = mol solute
volume of solution
L solution
What is the molarity of a solution prepared by dissolving 0.165 mol
sodium sulfate in enough water to give 125 mL of solution?
sodium = Na+
125 mL
sulfate = SO42-
1L
= 0.125 L
1000 mL
sodium sulfate = Na2SO4
M = 0.165 mol Na2SO4 = 1.32 M
0.125 L soln
[Na2SO4] = 1.32 M
Solution Composition
molarity = M = amount of solute = mol solute
volume of solution
L solution
How many moles of HNO3 are present in 2.0 L of 0.200 M HNO3
solution?
2.0 L 0.200 mol HNO3
L soln
= 0.40 mol HNO3
How many moles of ions are present in this solution?
• HNO3 is a strong acid, so in water it dissociates into H+ and NO3- ions
• Each HNO3 molecule dissociates into 2 ions
0.40 mol HNO3
2 mol ions
1 mol HNO3
= 0.80 mol ions
Solution Composition
molarity = M = amount of solute = mol solute
volume of solution
L solution
How many grams of Na2SO4 are required to make 350 mL of 0.500 M
Na2SO4?
0.350 L soln
0.500 mol Na2SO4 142.0 g Na2SO4
1 mol Na2SO4
1 L soln
= 24.9 g Na2SO4
What is the concentration of ions in this solution?
• Na2SO4 is ionic, so in water it dissociates into Na+ and SO42- ions
• Each Na2SO4 dissociates into 2 sodium ions and 1 sulfate ion (3 total)
0.500 mol Na2SO4
1 L soln
3 mol ions
= 1.50 M in ions
1 mol Na2SO4
= 1.00 M in Na+
= 0.50 M in SO42-
Dilution
dilution – the process of reducing the concentration of a solution by
adding solute (typically water)
moles of solute before dilution = moles of solute after dilution
How would you prepare 1.5 L of a 0.12 M HCl solution, using a 12.0
M stock solution?
M i V i = M fV f
12.0 M HCl x Vi = 0.12 M HCl x 1.5 L
Vi =
0.015 L
Start with 15 mL of the concentrated solution, then add H2O to get to
the desired final volume (1.5 L)