Acids and Bases

1
Acids and Bases
2
When we think of acids and bases we tend to think
of chemistry lab acids and bases like
But we are surrounded by acids and bases in the
world. Most of them are weak.
Acids cause lemons to be sour Acid rain to eat
away at sculptures Eat cavities in your
teeth Digest food in your stomach
3
Acids and Bases
What is an Acid and a Base?

• Properties of an Acid
• Tastes sour
• Turns litmus paper red
• Has a pH of less than 7
• Lemon juice and vinegar are good examples.

• Properties of a Base
• Turns litmus paper blue
• Has a pH greater than 7
• Taste bitter and have a slippery feel
• Most hand soaps and drain cleaners are bases

4
ACID pH is less than 7 BASE pH is more than
7 NEUTRAL pH 7
5
Strenuous exercise causes a buildup of lactic
acid in muscle tissue
Tea contains tannic acid
Fruit contains citric acid
Carbonated soft drinks contain carbonic acid and
phosphoric acid
Acid rain (nitric /sulfuric acid corroding a
limestone sculpture.
6
So what happens when an acid and base mix??

• NEUTRALIZATION REACTION!
• Acid Base ? Water Salt
• i.e.) Vinegar Baking Soda ? Water Salt
  Carbon dioxide
• Think of the VOLCANO you made in
  elementary school

7
Another Neutralization Reaction (Alka Seltzer)

• ALKA SELTZER made of citric acid and baking
  soda.
• When the tablet hits water, the water acts as a
  solvent converting the two formerly solid
  reagents into liquids allowing them to react.
• Reaction
• Citric Acid Baking Soda ? Water Sodium
  citrate (salt) CO2
• C6H8O7 NaHCO3 ? H2O Na3C6H5O7 CO2

8
ACID DEPOSITION

• Air pollutants (such as sulfur dioxide and
  nitrogen dioxide) can combine with water to form
  acid precipitation (rainwater that has become
  more acidic)
• Acid deposition is the more general term we use
  to describe this phenomena
• Air pollutants can come from both natural and
  human sources (volcanoes, forest fires, cars,
  factories)

9
Now its your turn

• Use the ACID DEPOSITION handout youve been given
  and pg. 64-65 of your text to fill in the
  diagrams of acid deposition.
• When you are finished, complete the following
  questions pg. 65 1-3

10
Acids and Bases in the ENVIRONMENT

• Due to air pollution, acid rain has caused some
  lakes in Canada to become acidic.
• Natural limestone (CaCO3) is a base used in to
  neutralize lakes. This technique is called
  liming.
• The calcium carbonate neutralizes the acidic
  water, thus raising the pH of the lake water.

11
So what were the bad air pollutants that cause
acid rain?

• Nitrogen oxide and sulfur dioxide
• The best way to reduce acid rain is to prevent it
  from even forming.
• So how do we reduce the amount of NO2 and SO2 in
  the air?
• REMOVE THE SULFUR

12
How do you remove sulfur?
13
Sweet Natural Gas

• This sulfur has been removed from sour natural
  gas before it is sent to consumers.
• Since sulfur emissions are one of the main causes
  of acid precipitation, removing the sulfur from
  the fuel before burning it will reduce acid
  precipitation

14
Scrubbing

• Some coal also contains sulfur. When this coal
  is burned, the sulfurous emissions can return to
  Earth as acid precipitation.
• To help prevent this, a device known as a
  scrubber is installed on the smokestacks of many
  industrial plants that burn coal.

15

• Turn to pg. 68, and in the space below draw
  Figure 4.8 and describe how a scrubber removes
  sulfur.

16
Corrosion of Iron
17
CORROSION

• Corrosion refers to any process that chemically
  breaks down or degrades metal.
• The best known type of corrosion is the rusting
  of iron.
• Most metals will rust, but the corrosion of iron
  is a serious problem as this metal is widely
  used.
• As rust flakes off an iron structure, more metal
  is exposed to the environment. This weakens the
  structure over time and can make the structure
  unsafe.

18
4Fe(s) 3O2(g) ? 2Fe2O3(s)

• What type of reaction is above?
• (composition, decomposition, combustion or
  neutralization)
• COMPOSITION
• Element Element ? Compound
• Although it is not included in the chemical
  equation, water is also required for rusting to
  occur.

19
Solving the Problem of Corrosion

• The rusting of the steel used to reinforce
  concrete buildings or bridges or pipelines can
  cause these structures to fail.
• Repairing or replacing these structures costs
  millions of dollars
• So how do you prevent rusting?

20

• 1) Painting this provides metals with a
  protective coating of paint.
• Painting over metal prevents oxygen and water
  from reaching the surface of the metal. This
  explains why steel beams are often painted red or
  green.
• However, once the paint chips off, water and
  oxygen are free to attack the steel, and rust
  blisters grow rapidly.

21

• 2) Galvanizing
• Galvanization is a process of applying a zinc
  coating to iron or steel. This involves
  immersing the metal in a bath containing molten
  zinc.
• This process coats the metal with a layer of
  zinc that provides a protective barrier between
  the metal and the environment.
• The galvanized coating resists chipping and
  cracking.

22

• 3) Sacrificial Metal
• Underground oil pipelines have bars of a second
  metal, such as magnesium, buried with the
  pipeline.
• The magnesium will corrode but the pipeline will
  not. In this case, the magnesium is sacrificed
  in order to protect the pipeline.
• It is much easier and cheaper to replace bars of
  magnesium rather than repair a ruptured pipeline