2. Lesson Objectives
By the end of the lesson, students sbat:
•Describe acids and alkalis
– Meaning of an acid and examples
– Meaning of an alkali and examples
•State the properties of acids and alkalis
•State the reaction of acid with metal to
produce hydrogen gas
•State the reaction of acid with carbonate to
produce carbon dioxide gas.
3. Lesson Objectives
• State the reaction of acid with alkali to
produce salt and water.
• State the uses of acids and alkalis in daily
life
• Describe indicators
– Litmus indicator and simple test for acids and
alkalis
– Universal indicator (idea of pH)
– pH meter and pH sensor
4. Lesson Objectives
• Show an understanding that indicators are
substances that change colour when an
acid or alkali is added to them.
5. Recap
• Mixtures can be classified as solutions and
suspensions.
• The differences between a solution and a
suspension are:
Properties
Formation
Appearance
Homgeneous
When left to
stand
When filtered
Examples
Solutions
A solute dissolves in the solvent
Suspensions
Insoluble solids mixed
with a liquid / gas
Clear, transparent
Cloudy, opaque
Yes
No
Solute particles do not separate from Solid particles sink to
solvent.
bottom
No residue is left on filter paper
Residue is left on filter
paper
Salt dissolved in water
Chalk in water
6. Acids
• An acid is an example of a solution.
• Common acids
Name
Chemical
formula
Hydrochloric
acid
Nitric acid
HCl
HNO3
Sulfuric acid
H2SO4
Explanation
Hydro- from hydrogen, -chlor
from chlorine
Nitr- from nitrogen (contains
nitrogen)
Sulfur- contains sulfur
7. Acids
• What is common in the formula?
– They all have H (hydrogen) in them.
• Hence, an acid is a substance which
produces hydrogen ions in water.
10. Chemical Properties of Acids
• Acids react with metals to
produce salt and hydrogen
gas.
• When a piece of metal is
placed into an acid, a gas,
hydrogen, is formed.
• Effervescence in the
solution will be observed.
11. Hydrogen is a colourless and odourless gas.
acid + metal → salt + hydrogen
• To confirm that gas produced is hydrogen,
Test: Place a lighted splint in the gas.
Observation: The splint will be extinguished with
a ‘pop’ sound.
12. Think
• Why is vinegar often sold in
glass bottles rather than tin
cans?
Vinegar is an acid. The acid will
react with the metal containers, it
will corrode the metal containers.
13. Chemical Properties of Acids
• Acids react with carbonates to produce
salt, carbon dioxide and water.
acid + carbonate → salt + carbon + water
dioxide
• Observation:
– Effervescence is observed
14. Test for Carbon Dioxide
• How do we know that the
gas is carbon dioxide?
• Test:
delivery tube
– Bubble the gas into
limewater.
limewater
• Observation:
– White precipitate is
observed in limewater.
acid +
carbonate
15. Think!
Indigestion pills often contain the
substances, sodium bicarbonate, calcium
carbonate and magnesium carbonate, to
react with the excess acid in the stomach.
Why is it that when these pills are consumed,
may result in frequent burping?
When the stomach acid reacts with the
carbonates, carbon dioxide is formed.
16. Alkalis
• Common alkalis:
– Sodium hydroxide
– Potassium hydroxide
– Calcium hydroxide
NaOH
KOH
Ca(OH)2
– Ammonium hydroxide
NH4OH
• What do you see in common?
– Hydroxide ions
An alkali is a substance that produces
hydroxide ions in water.
17. Physical Properties of Alkalis
corrosive
soapy feel
bitter taste
good
conductors of
electricity
22. pH
• The smaller the pH value, the more acidic the
substance.
• The bigger the pH value, the more alkaline the
substance.
• pH 7 indicates that the substance is neither
acidic nor alkaline (neutral)
23. More Properties
• Acids have a pH of less than 7.
• Alkalis have a pH of more than 7.
• When an acid (pH <7) reacts with an alkali
(pH >7) the resulting mixture is neutral.
• The reaction is known as neutralisation.
acid + alkali → salt + water
24. Neutralisation
Applications
Brushing teeth with
toothpaste
Explanation
Toothpaste is slightly alkaline. It neutralises
the acid left when bacteria feeds on the food
left in the teeth.
Control of pH of soil
Lime (calcium oxide) is added to soil to
neutralise the acidic soil. Some plants grow
better in slightly alkaline soil. E.g. Turnips,
cabbage, chrysanthemum.
Using conditioner after Shampoo is alkaline. It makes hair feel dry
shampooing hair
and coarse. Conditioners are slightly acidic,
it neutralises the shampoo left in the hair.
Taking indigestion pills Indigestion is usually a result of excessive
for indigestion
acid in the stomach. Taking indigestion
tablets which contain sodium bicarbonate
neutralises the excessive acid.
25. Indicators
• Indicators are substances which indicate if
a substance is acidic or alkaline.
• Examples of indicators:
– Litmus
• In an acid, blue litmus turns red
• In an alkali, red litmus turns blue
26. Indicators
– Universal Indicator
• measures pH
• green in neutral solutions.
• Red/orange in acidic solutions.
• Blue/purple in alkaline solutions.
