CH-2 (ACIDS BASES AND SALTS) Class-10 | NCERT Topper Notes

Chapter-2
Acids, Bases And Salts

ACIDS :

• These are the substances which have sour taste.
• These turn blue litmus solution red.
• They give H⁺ ions in aqueous solution.
• The term 'acid' has been derived from the Latin word, acidus, which means sour.

Strong Acids : HCl, H₂SO₄, HNO₃
Weak Acids : CH₃COOH, Oxalic acid, Lactic acid.
Concentrated Acid : Having more amount of acid + less amount of water
Dilute Acid : Having more amount of water + less amount of acid.

BASES :

• These are the substance which are bitter in taste and soapy in touch.
• They turn red litmus solutin blue.
• They give OH^- ions in aqueous solutin.

Strong Acids : NaOH, KOH, Ca(OH)₂
Weak Acids : NH₄OH
Alkalis : These are bases which are soluble in water [NaOH, KOH, Ca(OH)₂.

SALTS :

These are the compounds formed from reaction of acid and base.
Example :
NaCl, KCl

INDICATORS :

These are the substances which change thei colour/smell in different types of substances.

TYPES OF INDICATORS

Natural indicators	Synthetic indicators	Olfactory indicators
→ Found in nature in plants.	→ These are chemical substances.	→ These substances have different colour in acid and bases.
→ Litmus, red cabbage leaves extract, flowers of hydrangea plant, turmeric	→ Methyl orange, phenolphthalein

	S. No.	Indicator	Smell/Colour in acidic solutin	Smell/Colour in basic solutin
	1.	Litmus	Red	Blue
	2.	Red cabbage leaf extract	Red	Green
Natural Indicator
	3.	Flower of hydrangea plant	Blue	Pink
	4.	Turmeric	No change	Red
	1.	Phenolphthalein	Colourless	Pink
Synthetic Indicator
	2.	Methyl orange	Red	Yellow
	1.	Onion	Characteristic smell	No smell
Olfactory Indicator	2.	Vanilla essence	Retains smell	No smell
	3.	Clove oil	Retains smell	Loses smell

CHEMICAL PROPERTIES OF ACIDS AND BASES

Reaction of Metals With

Acids	Bases
Acid + Metal → Salt + Hydrogen gas E.g., 2HCl + Zn → ZnCl2 + H2	Base + Metal → Salt + Hydrogen gas E.g., 2NaOH + Zn → Na2ZnO2 + H2 → (Sodium zincate)

* Hydrogen gas released can be tested by bringing burning candle near gas bubbles, it burst with pop sound.

Reaction of Metal Carbonates/Metal Hydrogen Carbonates with

Acids	Bases
Acids + Metal Carbonates/Metal Hydrogen Carbonates → Salt + CO2 + H2O E.g., 2HCl + Na2CO3 → 2NaCl + CO2 + H2O HCl + NaHCO3 → NaCl + CO2 + H2O	Base + Metal Carbonate/ Metal Hydrogen Carbonate → No Reaction

* CO₂ can be tested by passing in through lime water.

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O (Lime water turns milky.)

When excess * CO₂ is passed,

CaCO₃ + CO₂ + H₂O → Ca(HCO)₃ (Milkiness disappears.)

Reaction of Acids and Bases With Each Other

Acid + Base → Salt + H₂O

Neutralisation Reaction : Reaction of acid with bae is called as neutralisation reaction.
E.g., HCl + NaOH → NaCl + H₂O
IF:
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

e.g.,
     CaO, MgO are basic oxides.
     Metallic Oxide + Acide → Salt + H₂O
     CaO + 2HCl → H₂O

Reaction of Non-metalic Oxides with Bases
Non-metallic oxides are acidic in nature.
Non-metallic Oxides + Base → Salt + H₂O
Co₂ + Ca(OH)₂ → CaCO₂ + H₂O

Reaction of Acid	+ Metal Carbonate → Salt + CO2 + Water + Metal → Salt + H2 + Metal Hydrogen Carbonate → Salt + CO2 + H2O + Metal Oxides → Salt + H2O + Base → Salt + H2O
Reaction of Base	+ Metal → Sal + H2 + Metal Carbonate → No Reaction + Metal Hydrogen Carbonate → No Reaction + Acid → Salt + H2 + Non Metallic oxide → Salt + H2

What do all Acids and Bases have In comman

• All acids have H⁺ ions in common.
• Acids produce H⁺ ions in solutin which are responsible for their acidic properites.
• All base have OH^- (hydroxyl ions) in common.

		Acids	→	H+ ions
All
		Bases	→	OH- ions

Acid or Base in Water Solution

• Acids produce H⁺ ions in presence of water.
• H⁺ ions cannot exist alone, they exist as H₃O⁺ (hydronium ions).

H⁺ + H₂O → H₃O⁺
HCl + H₂ → H₃O⁺ + Cl^-

Bases when dissolve in water gives OH^- ions.

NaOH ---H₂O→ Na⁺ + OH⁺
Mg(OH)₂ ---H₂O→ Mg²⁺ + 2OH⁺

• Bases soluble in water are called alkali.
•While diluting acids, it is recommended that the acid should be added to water and not water to acid becuase the process of dissolving an acid or a base in water is highly exothermic.

if water is added to acid the heat generated may cause the mixture to splash out and cause burns and the glass container may also break due to excessive local heating.

	Adding water to acid may
Cause mixture to splash out		Break the glass container

Mixing an acid or a base with H₂O results in decrease of concentration of ions (H₂O⁺/ OH^-) per unit volumem Such a process is called as dilution.

Strength of Acid and Base

Strength of acid or base can be estimeated using universal indicator.
Universal indicator : is a mixture of several indicators. It shows different colours at different concentration of H⁺ ions in the solutin.
pH Scale : A scale for measuring H⁺ ions concentration in a solutin. p in pH stands for 'potenz' a German word which means power.
pH = 7 → neutral solutin
pH less than 7 → acidic solution
pH more than 7 → basic solution

On diluting an acid : pH increases ↑
On diluting a base : pH decreases ↓

Importance of pH in everyday life

1. Plants and animals are pH sensitive	• Our body works within the pH range of 7-7.8. • When pH of rain water is less than 5.6, it is called acid rain.
2. pH of the soil	• Plants require a specific pH range for their healthy growth.
3. pH in our digestive system	• Our stomach produces HCl acid which helps in digestion. • During indigestion, stomach produces more acid and cause pain and irritaion. • To get rid of this pain, people uses antacid (mild base) like milk of magnesia [Mg?(OH)2] to neutralize excess acid.
4. pH change as cause of tooth decay	• Tooth decay starts when pH of mouth is lower than 5.5. • Tooth enamel made up of calcium phosphate (hardest substance in body) does not dissolve in water but corrodes when pH is lower than 5.5 due to acids produced by degradation of food particles by bacteria. • Using toothpaste (generally basic) tooth decay can be prevented.
5. Self defence by animals and plants through chemical warfare	• Bee sting leaves an acid which cause pain an irritaion. Use of a mild base like baking soda on stung area gives relief. • Stinging hair of nettle leaves inject methanoic acid casuing burning Sensation or pain. Rubbing with leaf of dock plant give relief.

pH of Salts :

(i) Strong Acid + Strong Base → Neutral Salt : pH = 7 eg. Nacl
(ii) Salt of strong acid + Weak base → Acidic Salt : pH < 7 eg. NH₄cl
(iii) Salt of strong base + Weak acid → Basic Salt : pH > 7 eg. CH₃C00na

Chemicals from Common Salt (NaCl)
↓

1.	2.	3.	4.	5.
↓ Sodium	↓ Bleaching	↓ Baking	↓ Washing	↓ Plaster of
Hydroxide	Power	Soda	Soda	Paris
(NaOH)	(CaOCl2)	(NaHCO3)	(Na2)CO3)10H2O)	(CaSO4½H2)O

1. Sodium Hydroxide (NaOH): When electricity is passed through an aqueous solutin of NaCl (brine), it decompose to form NaOH. (Chlor-alkali process).

2NaCl + 2H₂ → 2NaOH + Cl₂ + H₂

At anode : Cl₂gas
At cathode : H₂gas
Near cathode : NaOH solutin is formed.

Uses :

H₂ : Fuels, margarine
Cl₂ : Water treatment, PVC, CFC's
HCl : Cleaning steels, medicines
NaOH : Degreasing metals, soaps and paper making
Cl₂ + NaOH → Bleach : Household bleaches, bleaching fabrics

2. BleachingPowder (CaOCl₂) It us produced by the action if chlorine on dry slaked lime.

Cl₂ + Ca(OH)₂ → CaOCl₂ + H₂O

Uses :

(a) Bleaching cotton and linen in textile industry.
(b) Bleaching wood pulp in paper factories.
(c) Oxidizing agent in chemical industries.
(d) Disinfecting drinking

3. Baking Soda (Sodium Hydrogen Carbonate) (NaHCO₃) :

NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃

• It is mild non- corrosive base.
• When it is heated during cooking.
2NaHCO₃ → Na₂CO₃ + H₂O + CO₂

Uses :

(a) For making baking powder (mixture of baking soda and tartaric acid). When baking powder is heated or mixed with water, CO₂ is produced which causes bread and cake to rise making them sof and spongy.
(b) An ingerdient in antacid.
(c) Used in soda acids, fire extingusihers.

4. Washing Soda (Na₂CO₃.10H₂O) : Recrystallization of sodium carbonate gives washing soda. It is a basic salt.

Na₂CO₃ + 10H₂O → Na₂CO₃.10H₂O

Uses :

(a) In glass, soap and paper industry.
(b) Manufacture of borax.
(c) Cleaning agent for domestic purposes.
(d) For removing permanent hardness of water.

5. Plaster of Parts (Calcium sulphate hemihydrates) (CaSO₄.½H₂O) :
On heating gypsum (CaSO₄2H₂O) at 373K, it loses water molecules and becomes Plaster of Paris (POP)
It is a white powder and on mixing with water it changes to gypsum.

CaSO₄.½H₂O + 1½H₂O + 1½H₂O → CaSO₂2H₂O

Uses :

(a) Doctors use POP for supporting fractured bones.
(b) For making toys, material for decoration.
(c) For making surfaces smooth.
Water of Crystallization : It is a fixed number of water molecules present in one formula unit of a salt.

E.g.,
     CuSO₄5H₂O has 5 water molecules.
     Na₂CO₃10H₂O has 10 water molecules.
     CaSO₄2H₂O has 2 water molecules.