Acids
1. react with carbonates to produce carbon dioxide gas.
2. change pink phenolphthalein to colourless
3. make litmus paper red
4. make bromothymol blue turn yellow
5. taste sour
6. have a pH below 7
7. react with most metals and produce hydrogen gas

Bases
1.
don’t react with carbonates to produce carbon dioxide gas.
2. change colourless phenolphthalein to pink
3. make red litmus paper turn blue
4. make bromthymol blue turn blue
5. taste bitter
6. have a pH above 7

produce carbon dioxide gas.
NaCO
3
CO
2 bubbles
Acid

2.
phenolphthalein to pink
Phenolphthalein

turn red
Phenolphthalein
Litmus paper

blue turn yellow
Acid or base?
Bromthymol blue

A lemon tastes sour. Is it an acid or a base?

pH meter
Is this solution an acid or a base?

Is this solution an acid or a base?
H
2
Zn

Conceptual Definitions of Acids and Bases
A chemist named Arrhenius recognized acids were molecular compounds and as such didn't conduct electricity as liquids since they didn't release ions. But he observed that when acids were combined with water they did conduct electricity.
He also observed bases conducted electricity as liquids and when they were combined with water.
Bases were ionic but acids weren't.

Arrhenius’s Definition of Acids and Bases
Acids are substances which react in water and produce hydronium ions.
HCl (g) + H
2
0 -------> H
3
0 1+
(aq) + Cl 1-
(aq)
Bases are substances which react with water and produce hydroxide ions.
NH
3
(g) + H
2
0 ------> NH
4
1+
(aq) + OH 1-
(aq)

Homework from Nelson
Pg. 367 #1-7,

This concept has its limitations however. Can’t substances be classified as acids or bases without the involvement of water?

Bronstead's and Lowry's Definition of
Acids and Bases
Acids are substances which donate protons and bases are substances which accept protons .
In the examples above HCl (g) is an acid because it donates protons to H
2
O molecules and NH
3 is a base because it accepts protons from H
2
O molecules.

Conjugate Acid - Base Pairs - When using the
Bronsted concept for acids and bases it is convenient to consider all acid - base reactions as reversible equilibria.
For instance when sulfurous acid, H
2
SO
3 with water the following equilibrium is reacts established: conjugate pair acid
H
2
SO
3 base
+ H
2
O acid base
H
3
0 1+ + HSO
3
1conjugate pair

conjugate pair acid
H
2
SO
3 base
+ H
2
O acid
H
3 base
0 1+ + HSO
3
1conjugate pair
In the forward direction the H
2
SO
3 is the proton donor so it’s the acid and the H
2
O is the proton acceptor so it’s the base . In the reverse direction the H
3
0 1+ is the proton donor so it’s the acid and the
HSO
3
1proton acceptor so it’s a base . is the

conjugate pair acid
H
2
SO
3 base
+ H
2
O acid base
H
3
0 1+ + HSO
3
1conjugate pair
When looking at both forward and reverse reactions it is easy to pick out a pair of molecules which differ by a single proton (H atom without its electron).
These pairs are called conjugate acid-base pairs.

Homework from Nelson
Pg. 389 # 17-20
Pg. 392 # 8-11

Why do acids of equal concentration have different levels of conductivity?
Some acids are stronger than others.
Why?
Let's look at a container of water.

Water molecules

H Cl molecules

Strong acids and bases
Totally ionize

Water molecules

H F molecules

Only 1/5 ionized
20% ionization
Weak acid

Strength of Acids and Bases is determined by the degree to which a substance produces ions in solution.
A strong acid or base is a substance which completely ionizes. In other words if 100 molecules of a strong acid like HCl are placed in water all 100 of them will react with H
2
O producing 100 H
3
O 1+ ions and 100 Cl 1ions.
Weak acids and bases only partially ionize.
Strong Acid - the reaction below goes to completion.
HCl (g) + H
2
0 --------> H
3
0 1+
(aq) + Cl 1-
(aq)

Weak Acid - the reaction occurs to a limited extent. In the example below if 100 acetic acid molecules are placed in water only a few of them will successfully react with water molecules producing hydronium ions. Most CH
3
COO H molecules remain intact.
CH
3
COO H + H
2
0 H
3
0 1+
(aq)
+ CH
3
COO 1-
(aq)

Strong Acids in order of decreasing strength are
H ClO
4
, H I, H Br, H
2
SO
4
, H Cl, H NO
3
Acid strength has to do with the ease with which an acid can lose a proton. If the binary acid strengths ( H I, H Br, H Cl) are compared it can be seen that H I is the strongest acid of this group because its iodide ion is the largest of the group so the force between the hydrogen ion and the iodide ion is the weakest so it loses its proton most easily.

H 1+
Cl 1-
H 1+
Br 1-
Force is strongest since the ions are closest
Remember the weaker the force the stronger the acid
H 1+ I 1-
Force is weakest since the ions are furthest

Strong Bases include hydroxides of group 1A and Ca 2+ , Ba 2+ , and Sr 2+ .
A table with the remaining moderate and weak bases can be found on page
615. As with acids the weaker the bonds, the stronger the base since liberation of OH 1ions is easiest when the bonds are weakest.

Polyprotic Acids donate protons in steps. For instance carbonic acid, H
2
CO
3 has two protons to donate and it does this in two steps: step 1
H
2
CO
3
+ H
2
0 HCO
3
1+ H
3
0 1+ step 2
H CO
3
1+ H
2
0 CO
3
2+ H
3
0 1+ note : The arrows are constructed in this manner to show the reverse reaction has a greater tendency than the forward reaction.

Amphoteric (Amphiprotic) Substances can behave as both acids or bases dependent on the circumstances. Water molecules, for instance, can sometimes except protons and behave as bases or donate protons and behave as acids.
HBr
(g)
+ H
2
O base
H
3
0 1+
( aq)
+ Br 1-
(aq)
NH
3(g)
+ H
2
O acid
0H 1-(aq) + NH
4
1+(aq)

Homework -
Pg. 386 # 15,16
Pg. 379 # 1-5

Aqueous solutions can be classified as acidic, basic, or neutral. This classification scheme is based on the quantities of 2 ions, hydronium ion, H
3
0 1+ and hydroxide ion, OH 1. Where do these ions come from in solutions of pure water?
Water molecules in motion will randomly collide with one another. When this happens occasionally a hydrogen nucleus from one molecule will be transferred from one molecule to the other. This can be illustrated .

Notice the nucleus of one hydrogen atom, a proton, was transferred, but the electron pair was left behind. This produces the H
3
0 1+ ion (hydronium) and the OH 1ion
(hydroxide)

Hydronium ion (H
3
O 1+ )
H
2
O + H
2
0 H
3
O 1+
(aq)
+ OH 1-
(aq)
Which is usually shortened to:
H
2
0 H 1+
(aq)
+ OH 1-
(aq)
Hydroxide ion (OH 1)

In mathematical terms pH = -log[H 1+ ] so if in an aqueous solution the
[H 1+ ] = 2.4 x 10 -8 , the pH is
7.62
Remember the whole number portion of a pH doesn’t count as a significant digit (SD), just like in the number 2.4 x 10 -8 the exponent -8 doesn’t count as a SD.

pH
1.45
[H 1+ ]
[H 1+ ] =
-pH
[H 1+ ] =
-1.45
3.5 x 10 -2 mol/L

[H 1+ ]
6.2 x 10 -2 mol/L
pH
pH = -log [H
] pH = -log 6.2 x 10
pH = 1.21

-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
N
Increasing acidity e
How much more acidic is pH 1 than u pH 5?
10 000 x’s more acidic than t r
What pH is 1000x’s a l pH 2? pH of -1
Increasing basicity
Since this is a logarithmic scale pH 9 is 10x’s more basic than pH 8, pH
12 is 1000 x’s more basic than pH 9

Homework
Pg. 371 # 1-6
Pg. 375 # 1-6

Acids and bases, when combined in equal quantities, neutralize each other forming salt and water.
1+ 11+ 1-
HCl + NaOH
1+ 11+ 1-
HOH + NaCl
1+ 2-
3 H
2
SO
4
3+ 1-
3
6
1+ 13+ 2-
HOH + Al(SO
2
4
)
3
This neutralization can be used to determine the concentrations or molar masses of unknowns.
If the right indicator is placed in an acid or a base it will turn colour at the instant of neutralization.

Standardizing a Base -
(Determining its concentration)
When a solution of NaOH or KOH is prepared from its solid reagent it will react with water in the air as it is being massed. This means the mass of base measured is less than the recorded quantity.
If a massed quantity of stable acid (one which doesn’t react with the atmosphere) is placed in a flask and dissolved in distilled water the concentration of the basic solution can be determined by measuring the volume of base needed to neutralize it.

buret
Erlenmeyer flask
Magnetic stirrer

When the solution turns pink the number
# of mol of acid = # of mol of base equivalence pt.
Titrant - NaOH solution
18.31 mL
4.21 mL
22.52 mL m = 0.21 g
M = 204.22 g/mol
0.10 - 0.30 g of potassium hydrogen phthalate distilled water few drops phenolphthalein

1+ 11+ 1-
HX + NaOH
1+ 11+ 1-
HOH + NaX
Given m
HX
M
HX
= 0.21g
= 204.22 g/mol
V
NaOH
= 4.21 mL
C
NaOH
= ?
When the solution turns pink n HX = n NaOH m a
/M a
C b
=
= m a
/
C b
M
V b a
/ V b
C b
C b
= 0.21 g / (204.22 g/mol )(0.00421 L)
= 0.24 mol/L

Homework
Pg 399 # 1-9
Pg 401 # 1-3

mL
0.00
1.00
2.00
Estimate - 0.77
0.70
0.72
0.74
0.76
0.78
0.80

Measurements with burets must have 2 decimal places.
Don’t record 1.1 instead record
1.10
mL
The extra zero tells us the measuring instrument measures to the nearest tenth of a mL.
The last digit of any measurement is an estimated value.
0.00
1.00
2.00

Measuring the Concentration of a Vinegar
Solution
A measured volume of vinegar is placed in an
Erlenmeyer Flask using a pipette.
The standardized base from the 1st part of the experiment is placed in the buret

buret
Erlenmeyer flask
Magnetic stirrer

When the solution turns pink the number
# of mol of acid = # of mol of base equivalence pt.
Titrant - NaOH solution
22.52 mL
4.21 mL
18.31 mL
Measured vinegar solution
HC
2
H
3
O
2 few drops phenolphthalein

Determining the Molar Mass of an Unknown
Acid
Mass out from 0.10 - 0.30 g of the unknown acid in an Erlenmeyer flask.
Dissolve it in some distilled water then add a few drops of phenolphthalein.
Place the standardized base in the burette.
Measure the volume of base needed to reach the equivalence point. (End point is signaled by the solution turning and remaining pink)

buret
Erlenmeyer flask
Magnetic stirrer

When the solution turns pink the number
# of mol of acid = # of mol of base equivalence pt.
Titrant - NaOH solution of known concentration m = 0.21 g
M = ?
0.10 - 0.30 g of unknown acid distilled water few drops phenolphthalein