class 10 acid, bases, salt free pdf notes

Class 10 – Acid, Bases and Salt

1. Indicators – Indicators are the substances that indicate whether a solution is acid or base, by changing the colour of the solution.
2. Acids are sour in taste & change the colour blue litmus to red.
3. Bases are bitter in taste & change the colour red litmus to blue.
4. Natural indicator – Litmus, Petunia, Geranium, Turmeric, Hydrangea.
5. Synthetic indicator – Methyl orange, Phenolphthalein.
6. Litmus → purple dye → obtained from lichen (plant belonging to phyllum thallophyta).
7. Indicators are also called as acid-base indicator.
8. Olfactory indicators – The substance that changes its odour in acidic/basic medium.
   Ex: vanilla, onion, cloves.

Natural Indicator

Natural indicator	Colour in acidic medium	Colour in basic medium
1) Litmus (purple)	Red	Blue
2) Red cabbage (dark leaf extract – blue/purple)	Red	Green / Yellow
3) Flowers of Hydrangea plant	Blue (acid soil)	Pink (basic soil)
4) Turmeric (yellow)	No change	Red

In neutral soil – purple flowers / mix of blue & pink on single shrub.

Synthetic Indicators

Synthetic indicator	Colour in acidic medium	Basic medium
1) Phenolphthalein (colourless)	Colourless	Pink
2) Methyl orange (orange)	Red	Yellow

Olfactory Indicators

Indicator	Characteristic smell	In acidic medium	In basic medium
1) Onion	Characteristic smell	No smell	No smell
2) Vanilla essence	Retain smell	Retain smell	No smell
3) Clove oil	Retain smell	Retain smell	Loses smell

Difference between Acids & Bases

Acids	Bases
Acid is derived from Latin word “acidus”, it means sour. It has sour taste.	Bases are substances bitter in taste and soapy in touch.
They turn blue litmus to red.	They turn red litmus to blue.
They give H⁺ ions in aqueous solution.	They give OH⁻ ions in aqueous solution.
Types of acids: strong acids, weak acids, concentrated acids, dilute acids.	Types of bases: strong bases, weak bases, alkalis.
Strong acids: HCl, H₂SO₄, HNO₃ (Hydrochloric acid, Sulphuric acid, Nitric acid)	Strong bases: NaOH, KOH, Ca(OH)₂
Weak acids: CH₃COOH (acetic acid), oxalic acid, lactic acid	Weak base: NH₄OH (Ammonium hydroxide)

Note:

Concentrated acids = More acid + less water
Dilute acids = More water + less acid

Alkalis = Bases that are soluble in water
Ex: NaOH, KOH, Ca(OH)₂

Reaction of Metals with Acid & Base

Acid

1. Acid + Metal → Salt + H₂ gas

Ex:
2HCl + Zn → ZnCl₂ + H₂

Base

Base + Metal → Salt + H₂ gas

2NaOH + Zn → Na₂ZnO₂ + H₂
Na₂ZnO₂ → Sodium zincate

Note: All metals do not react with bases.
Metal must be more reactive than metals present in base for the reaction to take place.

H₂ gas released tested by bringing burning candle near gas bubbles, it burst with pop sound.

Reaction of Acid with Metal Carbonates and Metal Hydrogen Carbonates

(also called as bicarbonate)

Metal carbonate / Metal hydrogen carbonate + Acid → Salt + CO₂ + H₂O

1. 2HCl + Na₂CO₃ → 2NaCl + CO₂ + H₂O
2. HCl + NaHCO₃ → NaCl + CO₂ + H₂O

[ Reactivity level must be higher to react with either acid or base ]

Evolution of CO₂ gas can be tested by passing it through lime water.

• It turns to milky.
• When excess CO₂ is passed, milkiness disappears.

CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂
(calcium bicarbonate)

Base + Metal carbonate / Metal hydrogen carbonate → No reaction

Neutralisation Reaction

Reaction of acid with bases called as neutralisation reaction.

Acid + Base → Salt + H₂O

Ex:
HCl + NaOH → NaCl + H₂O

Types of Neutralisation

Strong acid + weak base → acidic salt + H₂O
Weak acid + strong base → basic salt + H₂O
Strong acid + strong base → neutral salt + H₂O
Weak acid + weak base → neutral salt + H₂O

Reaction of Metallic Oxides with Acids

Metallic oxides are basic in nature.

Metallic oxide + Acid → Salt + H₂O

Ex:
CaO + 2HCl → CaCl₂ + H₂O
MgO + 2HCl → MgCl₂ + H₂O

CaO, MgO are basic oxides.

Reaction of Non-Metallic Oxides with Bases

Non-metallic oxides are acidic in nature.

Non-metallic oxide + Base → Salt + H₂O

Example:
CO₂ + Ca(OH)₂ → CaCO₃ + H₂O

(Calcium hydroxide → Calcium carbonate)

RECALL

Reactions of Acids

1. Acid + Metal → Salt + H₂
2. Acid + Metal carbonate → Salt + CO₂ + H₂O
3. Acid + Metal hydrogen carbonate → Salt + CO₂ + H₂O
4. Acid + Base → Salt + H₂O
5. Acid + Metallic oxide → Salt + H₂O

Reactions of Bases

1. Base + Metal → Salt + H₂
2. Base + Metal carbonate → No reaction
3. Base + Metal hydrogen carbonate → No reaction
4. Base + Acid → Salt + H₂O
5. Base + Non-metallic oxide → Salt + H₂O

Ions in Solution

1. All acids produce H⁺ ions in solution.
2. All bases produce OH⁻ ions in solution.

H⁺ = Hydrogen ion
OH⁻ = Hydroxyl ion

Acids in Water

• Acids produce H⁺ ions in water.
• H⁺ ions cannot exist alone.
• They exist as H₃O⁺ (Hydronium ions).

Acids in Water

H⁺ + H₂O → H₃O⁺

HCl + H₂O → H₃O⁺ + Cl⁻

While diluting acids, acid should be added to water.
Not water to acid.

This is because the process of dissolving acid/base in water is highly exothermic (releases heat).

Bases in Water

1. Bases that are soluble in water are called alkalis.
2. NaOH (s) + H₂O → Na⁺ + OH⁻
3. Mg(OH)₂ + H₂O → Mg²⁺ + 2OH⁻
4. KOH (s) + H₂O → K⁺ (aq) + OH⁻

Dilution

Mixing of acid or base with water results in the decrease of concentration of (H₃O⁺ / OH⁻) per unit volume.

Universal Indicator

a) It is a mixture of several indicators.
b) It shows different colours at different concentrations of H⁺ ions in a solution.

pH Scale

1. A scale for measuring hydrogen ion concentration in a solution is called the pH scale.
2. p stands for “potenz” in German meaning power.
3. pH of a neutral solution is 7.

Acidic solution = 0 – 7
(Increase in concentration of H⁺ ions)

Basic solution = 7 – 14
(Increase in concentration of OH⁻ ions)

Strong and Weak Acids

Strong acid = Acids that give rise to more H⁺ ions.
Weak acid = Acids that give rise to less H⁺ ions.

Few Examples of pH Value

1. Gastric juice = pH 1.2
2. Lemon juice = pH 2.2
3. Pure water, blood = pH 7.4
4. Milk of magnesia (Mg(OH)₂) = pH 10
5. NaOH solution = pH 14

Importance of pH in Everyday Life

1. Our body pH = 7.0 to 7.8
2. pH of acid rain = less than 5.6

How pH of Acid Rain Affects Aquatic Life

When acid rain flows into rivers, it lowers the pH of river water and the survival of aquatic life becomes difficult.

Why Life Cannot Exist on Venus?

1. Venus atmosphere is thick.
2. Atmosphere of Venus is made up of white and yellowish clouds of H₂SO₄.
3. Major component of atmosphere is (95–97%) of CO₂.

What is the Ideal pH for the Growth of Plants?

1. Optimal pH of soil varies from 5.5 to 7.0.
2. It should be neither too alkaline nor acidic in nature.
3. Change in pH of soil affects the availability of nutrients for growth of plants.

pH in Our Digestive System

1. Stomach produces HCl for digestion of food.
2. During indigestion, stomach produces too much HCl that causes pain and irritation.
3. To get rid of this, we use antacids.
4. Antacids are bases that neutralise the excess acid.

Example:
Magnesium hydroxide Mg(OH)₂ – Milk of Magnesia

pH in Tooth Decay

1. Tooth enamel is made up of calcium hydroxyapatite
   Ca₅(PO₄)₃OH (crystalline form of calcium phosphate).
2. Tooth decay starts when pH of mouth is below 5.5.
3. Enamel does not dissolve in water, but starts to corrode when pH is less than 5.5.
4. The bacteria in the mouth, after eating, start to act on remaining food particles.
5. It produces acid that degrades the food particles and sugar.
6. The best way to prevent this is to clean the mouth after eating the food.
7. Use toothpaste that are basic, so that it can neutralise the excess acid and prevent tooth decay.

Nature’s Self Defence

1. Bee’s sting – It causes pain and irritation.
   Using mild base, baking soda gives relief.
2. Nettle leaves stinging hair – Insect methanoic acid causes burning pain.
   Remedy – Rubbing the area with leaf of dock plant.

Nature’s Acids

1. Vinegar – Acetic acid
2. Curd – Lactic acid
3. Orange, lemon – Citric acid
4. Tamarind – Tartaric acid
5. Tomato – Oxalic acid
6. Ant sting / Nettle sting – Methanoic acid (Formic acid)
   HCOOH

SALT

1. Salt of strong acid + strong base = Neutral (pH = 7)
2. Salt of strong acid + weak base = Acidic (pH < 7)
3. Salt of weak acid + strong base = Basic (pH > 7)

Common Salt

1. Salt formed by combination of HCl and NaOH is called NaCl.
2. Large crystals are brown due to impurities.
   This is called Rock salt. It is mined like coal.
3. Now common salt is a raw material for various chemicals.

NaOH (Sodium Hydroxide)

a) When electricity is passed through aqueous solution of NaCl (brine), it decomposes to form NaOH.

b) This process is called Chlor-alkali process.

c) Products formed are Chlorine, NaOH, Hydrogen.

d) Chemical equation:
2NaCl (aq) + 2H₂O (l) → 2NaOH (aq) + Cl₂ (g) + H₂ (g)

e) Cl₂ is formed at anode, H₂ at cathode.
NaOH is formed near cathode.

Uses

1. Cl₂ – used in water treatment, swimming pools, PVC, disinfectant, CFC, pesticides.
2. H₂ – used as fuels, margarine, NH₄ for fertilisers.
3. Brine – degreasing metals, soaps, detergents.

Bleaching Powder

1. Cl₂ gas produced by electrolysis of aqueous solution of NaCl.
2. It is used for the manufacture of bleaching powder.

Preparation:
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
(Slaked lime → Bleaching powder)

Uses of Bleaching Powder

1. It is used as an oxidising agent in many chemical industries.
2. It is used to make germ-free drinking water.
3. Textile industry – bleaching cotton, linen.
   Paper factories – bleaching wood pulp.
   Laundry – bleaching white clothes.

Baking Soda

1. Chemical name – Sodium hydrogen carbonate (NaHCO₃).
2. Preparation (Ammonia-soda process):
   NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃
3. NaHCO₃ is a mild, non-corrosive basic salt.
4. It is used to make crispy food and faster cooking.
   During cooking, this reaction takes place:

2NaHCO₃ —heat→ Na₂CO₃ + H₂O + CO₂

(Sodium carbonate)

Uses of Baking Soda

1. Baking powder = Baking soda + Tartaric acid

When baking powder is mixed with / heated with water:

NaHCO₃ + H⁺ → CO₂ + H₂O + Sodium salt of acid
(from any acid)

CO₂ produced causes the bread to rise and make it soft and spongy.

2. NaHCO₃ is an ingredient in antacids.
   Being alkaline, it neutralises excess acid in the stomach and provides relief.
3. It is used in soda-acid fire extinguishers.

Washing Soda

1. Chemical name = Na₂CO₃ · 10H₂O
2. Sodium carbonate is obtained by heating baking soda.
3. Recrystallisation of sodium carbonate gives washing soda.

Na₂CO₃ + 10H₂O → Na₂CO₃ · 10H₂O

Uses of Washing Soda

1. It is used in glass, soap, paper industries.
2. It is used to manufacture borax.
3. It is used as a cleaning agent for domestic purposes.

Are the Crystal Salts Dry?

Water of crystallisation – It is the fixed number of water molecules present in one formula unit of a salt.

Examples

1. Hydrated copper sulphate = CuSO₄ · 5H₂O
   It is blue in colour. When we heat these crystals, it turns white.
2. Gypsum = CaSO₄ · 2H₂O
   (2 water molecules as water of crystallisation)

Plaster of Paris (POP)

1. On heating gypsum at 373 K, it loses water molecules and becomes calcium sulphate hemihydrate.

CaSO₄ · 2H₂O —heat→ CaSO₄ · ½H₂O

This is Plaster of Paris.

2. POP is a white powder. On mixing with water, it changes to gypsum.

CaSO₄ · ½H₂O + 1½H₂O → CaSO₄ · 2H₂O
(Gypsum)

3. Uses of POP:
   • Used by doctors for supporting fractured bones in right position.
   • Used to make toys.
   • Used for making surfaces smooth.
   • Used as material for decoration.

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