1. Science for grade 7 Chapter - 8
Acids, Bases and Salts
Science for grade 7
Chapter - 8

2. Module Objectives Define acids, bases and salts.
Differentiate between acids and bases
Know uses of common acids, bases and salts
Define indicators
Explain neutralization reaction
Explain pH value

3. ACIDS Acids are sour to taste.
The word acid comes from the Latin word acidus, meaning sour.
Foods that contain acids:
Citrus fruits like lemon, orange, gooseberry,
Vinegar
Tamarind
Milk
Curd
A bee sting or the bite of a red ant produces a burning sensation because these insects inject Formic acid into the body when they sting or bite.

4. Mineral (inorganic) Acids
Types of Acids
Acids
Organic Acids
Mineral (inorganic) Acids
Acids that are prepared from minerals present in the earth are called mineral acids
Examples:
Sulphuric acid - H2SO4
Hydrochloric acid - HCl
Nitric acid - HNO3
Acids that occur naturally are called organic acids
Examples:
Organic Acid
Occurs in
Citric acid
lemon, orange
Tartaric acid
tamarind, grapes
Lactic acid
milk

5. Parts of an acid
An acid has two parts –the hydrogen part and the radical part.
A radical is a charged group of atoms.
When acids dissolve in water, they split up into their hydrogen part and radical part.
Acid
Hydrogen part
Radical part
HCl H+
Cl-
H2SO4
2H+
SO42-
HCl
Dissolves in H20
H Cl-
hydrogen ion
chloride ion
Dissolves in H20
2H SO42-
H2SO4
hydrogen ion
sulphate ion

6. Definition
An Acid is a compound which when dissolved in water gives hydrogen ions (H+) as the only positive ion.

7. Physical Properties of Acids
Taste
Sour
Conductivity
Acid in water makes water a good conductor of electricity
Solubility
Soluble in water. Dissolving acid in water is an exothermic reaction, i.e it gives out heat.
Corrosiveness
Very corrosive. Acids can destroy paper, wood, metals and cause burns on skin.
Litmus Effect
Blue litmus turns Red.

8. Chemical Properties of Acids

9. Chemical Properties of Acids

10. Uses of Acids Hydrochloric Acid (HCl) Nitric Acid (HNO3)
To manufacture glue
To purify common salt
In preparation of glucose and chlorides
For bleaching in textile industry
Nitric Acid (HNO3)
To etch designs on metals
To purify gold and silver
To extract metals from their ores
In the manufacture of dyes, perfumes, fertilizers, explosives

11. Uses of Acids Sulphuric Acid (H2SO4) Carbonic Acid Aqua Regia
To refine petrol
To manufacture detergents, plastics, paint
In paper and automobile industry
Carbonic Acid
To prepare soft drinks
Aqua Regia
To etch designs on gold and platinum

12. BASES Chemical compounds that are bitter to taste are called bases.
A base has two parts- metal part and hydroxyl part
Base
Metal part
Hydroxyl part
Na (OH)
Na+
(OH)-
Ca (OH)2
Ca2+
2(OH)-
Na(OH)
Dissolves in H20
Na (OH)-
sodium ion
hydroxide ion

13. Types of Bases All bases do not dissolve in water ALKALI NON-ALKALI
Bases that dissolve in water
Bases that do not dissolve in water
Sodium hydroxide
Aluminium hydroxide
Potassium hydroxide
Copper hydroxide

14. Physical Properties of Bases
Taste
Bitter
Feel
Soapy to touch
Conductivity
Good conductor of electricity
Corrosiveness
Some bases are corrosive
Litmus Effect
Red litmus turns Blue

15. Chemical properties Base + Acid Salt + Water Calcium hydroxide
Sulphuric Acid
Calcium sulphate
+ Water +
Sodium hydroxide
Hydrochloric Acid
Sodium chloride +
+ Water

16. Uses of bases Sodium hydroxide ( NaOH ) Calcium hydroxide ( Ca(OH)2 )
In textile, plastic industry
To manufacture medicine, paper
To refine petroleum
Calcium hydroxide ( Ca(OH)2 )
In white washing
As an antidote for acid poisoning
In manufacture of bleaching powder, cement
To remove fur from animal skin
Ammonium hydroxide ( NH4OH )
Remove ink from clothes and grease stains

17. Indicators
Indicators are chemical substances to indicate if a substance is acidic, basic or neutral.
Example: Litmus
ACID
BASE

18. Indicators

19. Neutralization
Acids react with bases to form respective salts and water. This reaction is called a neutralization reaction.
Base Acid
Salt + Water

20. Acid – Base Comparison

21. SALTS
Salts are prepared by the neutralization reaction of acids and bases
Base Acid
Salt + Water

22. Properties of salts
Most salts are solids with high melting and boiling point
Most salts are soluble in water
Salts that dissolve in water make the solution a good conductor of electricity

23. Some important salts Sodium chloride Sodium carbonate
Sodium bicarbonate
Copper sulphate
Potassium nitrate
Potash alum
Silver nitrate

24. Sodium chloride – Common Salt
Added to food
Used in pickling and curing of fish and meat
Used in pottery glazing

25. Sodium carbonate – Washing soda
To wash clothes
To refine petroleum
In manufacture of detergents, paper and glass

26. Sodium bicarbonate – Baking Soda
In bakery products like bread and cakes
As an antacid
In fire extinguishers

27. Other salts Copper sulphate Potassium nitrate Potash Alum
To manufacture medicines
Potassium nitrate
In glass and refrigeration industries
Potash Alum
In purification of water
Silver Nitrate
In developing films

28. pH value
The acidity or basic strength of substances can be measured using a special scale called the pH scale.
Most Acidic
Most Basic

29. Importance of pH The pH range suitable for the human body is 7 to 7.8
Stomach produces HCl
pH ranges in different parts of the body is shown below

30. Exercises
Choose the correct answer

31. Exercises

32. Exercises

33. Exercises

34. Exercises