Acids, Bases and SaltsScience for grade 7
Chapter - 8
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
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.
Types of Acids
• Acids that occur naturally are called organic acids
• Examples:
Organic Acid Occurs in
Citric acid lemon, orange
Tartaric acid tamarind, grapes
Lactic acid milk
• Acids that are prepared from minerals present in the earth are called mineral acids
• Examples: Sulphuric acid - H2SO4
Hydrochloric acid - HCl Nitric acid - HNO3
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 H+ + Cl-Dissolves in H20
hydrogen ion chloride ion
H2SO4
Dissolves in H20 2H+ + SO42-
hydrogen ion sulphate ion
Definition
An Acid is a compound which when dissolved in water gives hydrogen ions (H+) as the only positive ion.
Physical Properties of Acids
1. TasteSour
2. ConductivityAcid in water makes water a good conductor of electricity
3. SolubilitySoluble in water. Dissolving acid in water is an exothermic reaction, i.e it gives out heat.
4. CorrosivenessVery corrosive. Acids can destroy paper, wood, metals and cause burns on skin.
5. Litmus EffectBlue litmus turns Red.
Chemical Properties of Acids
Chemical Properties of Acids
Uses of Acids
1. Hydrochloric Acid (HCl) To manufacture glue To purify common salt In preparation of glucose and chlorides For bleaching in textile industry
2. 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
Uses of Acids
3. Sulphuric Acid (H2SO4) To refine petrol To manufacture detergents, plastics, paint In paper and automobile industry
4. Carbonic Acid To prepare soft drinks
5. Aqua Regia To etch designs on gold and platinum
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) Na+ + (OH)-Dissolves in H20
sodium ion hydroxide ion
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
Physical Properties of Bases
1. TasteBitter
2. FeelSoapy to touch
3. ConductivityGood conductor of electricity
4. CorrosivenessSome bases are corrosive
5. Litmus EffectRed litmus turns Blue
Chemical properties
Base + Acid Salt + Water
Calcium hydroxide
Calcium sulphate
+Sulphuric Acid
+ Water
Sodium hydroxide
Sodium chloride
+Hydrochloric Acid
+ Water
Uses of bases
1. Sodium hydroxide ( NaOH ) In textile, plastic industry To manufacture medicine, paper To refine petroleum
2. 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
3. Ammonium hydroxide ( NH4OH ) Remove ink from clothes and grease stains
Indicators
• Indicators are chemical substances to indicate if a substance is acidic, basic or neutral.
• Example: Litmus
BASE
ACID
Indicators
Neutralization
• Acids react with bases to form respective salts and water. This reaction is called a neutralization reaction.
Base + Acid Salt + Water
Acid – Base Comparison
SALTS
• Salts are prepared by the neutralization reaction of acids and bases
Base + Acid Salt + Water
Properties of salts
1. Most salts are solids with high melting and boiling point
2. Most salts are soluble in water3. Salts that dissolve in water make the solution
a good conductor of electricity
Some important salts
1. Sodium chloride 2. Sodium carbonate3. Sodium bicarbonate4. Copper sulphate5. Potassium nitrate6. Potash alum7. Silver nitrate
Sodium chloride – Common Salt
1. Added to food2. Used in pickling and curing of fish and meat3. Used in pottery glazing
Sodium carbonate – Washing soda
1. To wash clothes2. To refine petroleum3. In manufacture of detergents, paper and
glass
Sodium bicarbonate – Baking Soda
1. In bakery products like bread and cakes2. As an antacid3. In fire extinguishers
Other salts
1. Copper sulphate• To manufacture medicines
2. Potassium nitrate• In glass and refrigeration industries
3. Potash Alum• In purification of water
4. Silver Nitrate• In developing films
pH value
The acidity or basic strength of substances can be measured using a special scale called the pH scale.
Most Acidic Most Basic
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
ExercisesChoose the correct answer
Exercises
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Exercises