Acids, Bases & pH
WATER
Before understanding Acids and Bases, you must
understand water.
1. It is a polar covalent molecule. Like a
magnet.
-
+
-
+
WATER
1.
It is a polar covalent molecule. WHY???
Oxygen pulls on the electrons more than Hydrogen does.
-
+
-
+
WATER
Because water is POLAR (negative side and
positive side), what types of compounds will
it DISSOLVE easily?
Covalent or Ionic?
-
+
-
+
Ionic Compounds: Acids
Or written as HCl  H3O+ + Cl-
Ionic compounds that break apart (dissolve) in water to
form a hydronium ion, H3O+ (hydrogen ion, H+).
The more H+ ions released in water = STRONGER ACID
Acids
Or written as HCl  H3O+ + Cl-
When HCl is put in water, a Hydronium ion, H3O+
(hydrogen ion, H+) is formed.
Acids, Bases and pH
Why do we need to know?
The pH of a substance determines its physical and
chemical properties .
Acids
Characteristics of Acids
1. Taste Sour
2. React Strongly with Metals and
Carbonates (in soil and rocks)
3. Can burn your skin
4. Conduct electricity in water
5. Turn indicator red
Examples of Acids
1. Vinegar
2. Citrus fruits
3. Stomach Acid (HCl)
Ionic Compounds: Bases
NaOH  Na+ + OH-
Ionic compounds that break apart (dissolve) in water
to form a negatively charged hydroxide ion (OH-).
More OH- ions released in water = STRONGER BASE
Acids, Bases and pH
Why do we need to know?
The pH of a substance determines its physical and
chemical properties .
Bases
Characteristics of Bases
1. Taste bitter
2. Feel Slippery
3. Can burn your Skin
4. Turn indicator blue
5. Conduct electricity in water
Examples of Bases
1. Lye (Sodium Hydroxide)
2. Ammonia
3. Bleach
pH
What does it mean?
pH – potential of Hydrogen – the
ability to release H+
The more H+ released in water, the HIGHER
the pH.
Which one below releases more H+?
1. HBr  H3O+ + Bror written as
HBr  H+ + Br-
2. KOH  K+ + OH-
pH
Which has a greater ability to release H+ in
water? Which has HIGHER pH?
HBr  H+ + BrYES! And therefore this shows a higher pH
(potential of Hydrogen)
KOH  K+ + OHNO! And therefore this shows a lower pH
(potential of Hydrogen)
pH
COMPARE: WHAT ARE THEIR pH
VALUES?????
HBr  H+ + BrAbout 1 to 2
KOH  K+ + OHAbout 13 to 14
pH
pH – potential of Hydrogen – the ability to release H+
WHAT ABOUT NEUTRAL WATER?
H2O  H+ + OH-
What is the pH for this?
pH
pH – potential of Hydrogen – the ability to release H+
NEUTRAL WATER: H2O  H+ + OHNEUTRAL = pH 7
HOW DOES THIS HAPPEN?
pH
H2O  H3O+ + OHpH 7
Dissociation – the breaking apart of water into
ions. H3O+ = OH-
The pH Scale
Tells the concentration of (how many) hydrogen (H+)
ions in solution.
Hydrogen Ion Concentration in Moles/Liter at 25° C
pH
H+ conc.
0
1.0
1
0.1
2
0.01
3
0.001
4
0.0001
5
0.00001
6
0.000001
7
0.0000001
8
0.00000001
9
0.000000001
10
0.0000000001
11
0.00000000001
12
0.000000000001
13
0.0000000000001
14
0.00000000000001
The pH Scale
Tells the concentration of (or how many) hydrogen (H+)
ions in a water solution.
Each move up the scale is a jump of 10 TIMES.
HOW MANY TIMES?











How many times stronger is pH 3, than pH 4?
pH3 is 10 times stronger than pH4
Or another way, 1 jump up the scale equals 10 times more
H+ ions!
How many times stronger is pH 5, than pH 8?
3 jumps up the scale?
10 x 10 x 10
1,000 times more H+ ions! 1,000 times stronger!
How about pH 1 than pH 7?
6 jumps
10 x 10 x 10 x 10 x 10 x 10
1,000,000 times! 1,000,000 times MORE H+ ions!
The pH Scale


The 0 – 14 pH scale was created to show
amount of H+ ions in a water solution.
pH of a neutral solution = 7
H+ concentration = OH- concentration


Acidic pH values: 0 – 6, MAXIMUM = 0
Basic pH values: 8 – 14, MAXIMUM = 14
Indicator
Indicator – changes color as the pH changes, and
thus tells us the pH of a solution.
NEUTRALIZATION


What happens when an ACID is added to a
BASE ????
They react to form a salt and water
Hydrochloric Acid + Sodium Hydroxide  Water + Table Salt
HCl + NaOH  H2O + NaCl
Acids and Bases and Neutralization

One of the most important aspects of a living
system is the amount of acidity or alkalinity
NEUTRALIZATION:
Why do we need to know?


Control of pH is very
important
Control is accomplished with
buffers
pH
Why do we need to know?

Buffers neutralize
small amounts of
either an acid or
base.
pH
Why do we need to know?
Alkalinity – the ability of a stream to neutralize acids.
STOP HERE