Acids and Bases and use of indicators to find the nature of substances

The power point deals with acidic and basis substances. How are acids and bases classified further. It also deals with the use of various indicators in finding out the nature of acidic and basic substances.

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•Acids produce H
+
in solution,
example: HCl
•Bases produce OH
-
in solution,
example NaOH

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What is an acid?
everyday acids laboratory acids
Acidsare a group of chemicals.
Can you think of other examples of acids?

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What is a weak acid?
Strong acids cannot be touched and are corrosive.
Weak acids are safe to handle and have a sour taste.

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What is a strong acid?
Some acids, like those found in the laboratory or a car
battery, are very dangerous (too dangerous to taste or touch).
These acids are said to be corrosive as they can damage
other materials by wearing them away!They are strong acids.
Why must strong acids always be handled very carefully?

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What is a base?
everyday bases laboratory bases
Basesare another group of chemicals, the opposite of acids.
Can you think of other examples of bases?

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What is a weak base?
Bases are used for cleaning. Strong bases are caustic and
cause redness on the skin.
Weak bases are soapy and safe to touch.

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What is a strong base?
Some bases, like those in the laboratory or in cleaning
materials such as toilet cleaner, are too dangerous to touch.
These bases are said to be causticbecause they can burn
skin and damage other materials! They are strong bases.
Why must strong bases always be handled very carefully?

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The strength of an acid or base is measured by the pH scale.
What is the pH scale?
Each universal indicatorcolour is given a number called
the pH value.
Universal indicator can tell you the pH of a solution.
weak
base
weak
acid
strong
base
strong
acid
stronger basestrongeracid
neutral
12 3 4 5 6 78 9 10 1112 1314

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Are these substances acidic or basic?
Are they weak or strong?
12 14131211109876543
Substance pHDescription of acid/base
soda water 6
car battery acid1
soap 8
washing soda 10
stomach acid 2
oven cleaner 14
vinegar 4
very weak acid
very strong acid
very weak base
weak base
strong acid
very strong base
weak acid
baseacid
What type of substance?

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What is the pH?

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How can you test a liquid to find if it is an acid or an base?
An indicatoris a special chemical that changes
to a different colour in an acid or an base.
What is an indicator?
Litmus paperand litmus solutionare
examples of indicators.
Litmus is
red in acid.
Litmus is
blue in base.

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Litmus test experiment

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•Litmus paper cannot distinguish between a
weak acid and a strong acid (or weak base
and strong base).
•A better indicator is required…

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Litmus is used to show if a solution is acid or base.
Litmus doesnotshow if the acid or base is weak or strong.
What is universal indicator?
Universal indicatorhas a range of colours that indicate the
difference between weak or strong acids or bases.
stronger basestrongeracid
weak
base
weak
acid
strong
baseneutral
strong
acid

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#1: Neutralization
The GENERAL reaction betweenan acidandan base
is calledneutralization.
What happens to the pH value of the reaction mixture during
neutralization?
acid base a salt water
The pH value of the reaction mixture becomes closer to 7.

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#1: Neutralization
The EXAMPLE for the chemical reaction between anan
acidandan basecan be written as:
NaClHCl NaOH
H
2O

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#1: Neutralization
The GENERAL reaction between anan acidanda
carbonate can be written as:
saltacid carbonate H
2O
CO
2

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#1: Neutralization
The EXAMPLE of a chemical reaction between anan acid
anda carbonatecan be written as:
2NaCl2HCl Na
2CO
3 H
2O
CO
2

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#3: Metals with Acid
General Reaction:
salt
acid
metal
hydrogen
MgCl
2
HCl Mg H
2
Example:

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#3: Metals with Acid

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Summary Chart
Property Acid Base Salt
Definition produce H
+
produce OH
-
ionic compound
Example HCl, CH
3COOH NaOH, NH
3 NaCl
pH 1-2, 3-6 8 –11, 12 –14 7
red litmus red blue stays red
blue litmus red blue stays blue
Universal
indicator
red –yellow
ROY
blue –violet
BIV
green
G
taste sour
vinegar,
lemon juice
corrosive
feel soapy
household
cleaners
caustic
All acids, bases and salts dissolve in water.

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Summary of Reactions
#1: Neutralization
acid + base salt + water
#2: Carbonate with acid
acid + carbonate salt + water + carbon dioxide
#3: Metal with acid
acid + metalsalt + hydrogen

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Neutralization and indigestion

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Neutralizing stings
A beesting
isacidic.
A wasp sting
isalkaline.
Why can bicarbonate
of soda(pH 9) be used
to treat a bee sting?
Why can vinegar (pH 3)
be used to treat
a wasp sting?

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Neutralizing soil
Soils in different places can
be acidic, alkaline or neutral.
Many plants do not grow
well in acidic soil.
Why do farmers test soil
to check the pH?
Farmers often add an alkali to acidic soil to make their
plants grow better.
How does the alkali help to treat the acidic soil?

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Neutralizing acid rain
Gases emitted by cars, power
stations and factories mix with
rainwater in the atmosphere.
This rainwater has a pH <5.5.
Why is it called acid rain?
Acid rain can have a harmful
effect on the environment
killing trees, polluting lakes
and damaging buildings.
How can the effects of
acid rain be prevented?

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Glossary
acid –A chemical that has a pH less than 7.
base –A chemical that has a pH greater than 7 and
dissolves in water.
indicator –A special chemical that changes into different
colours in acid and base solutions.
neutral –A chemical with a pH of 7 that is not an acid or
a base.
neutralization –The chemical reaction between an acid
and a base.
pH scale –The range of values that shows how strong or
weak an acid or base is.
universal indicator –The indicator that shows the pH
value of a chemical.

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