acids, bases and salts science for grade 7 chapter - 8

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

Exercises

Exercises

Exercises