Class 10 Acids, Bases and Salts Notes

Notes Previous Years Questions Important Questions

Acids, Bases and Salts Notes

Physical properties of acids:-

• Acids are sour in taste.
• Acids are corrosive in touch.
• Acids turn blue litmus red.
• Acids give H⁺ ion in water.

Physical properties of bases:-

• Bases are bitter in taste.
• Bases are soapy in touch.
• Bases give OH^– ion in water.
• Bases turn red litmus blue.

Indicators:-

The substances which help us to distinguish between acids & bases are called indicators.

Some examples of natural indicators:-

• Litmus
• Turmeric
• China rose
• Red cabbage

Some examples of synthetic indicators:-

• Methyl orange
• Phenolphthalein

Litmus:-

• Litmus solution is extracted from lichen.
• Its original colour is purple.

Olfactory indicators:-

The substances whose odour (smell) changes in the presence of an acid or a base are called olfactory indicators. Ex:- Onion, clove, vanilla etc.

Reaction of acids with metals:-

Metal + Acid → Salt + Hydrogen

• 2Na + 2HCl → 2NaCl + H₂
• Mg + H₂SO₄ → MgSO₄ + H₂

Reaction of bases with metals:-

Metal + Base → Salt + Hydrogen

• Zn + 2NaOH → Na₂ZnO₂ + H₂
• Na₂ZnO₂ ⇒ Sodium Zincate

Hydrogen gas test:-

When we bring a burning candle to the mouth of test tube where hydrogen gas is evolving, it burns with pop sound.

Reaction of metal carbonates & metal hydrogen carbonates / metal bicarbonates with acids:-

• Metal carbonate/Metal bicarbonate + Acid → Salt + Water + Carbon dioxide
  • Na₂CO₃ +2HCl → 2NaCl + H₂O + CO₂
  • NaHCO₃ + HCl → NaCl + H₂O + CO₂
• This CO₂ gas turns lime water (slaked lime) milky when passed through it.
  • Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
  • CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂
  • Limestone, chalk and marble are different forms of calcium carbonate(CaCO₃).

Reaction of an acid and a base with each other:-

Neutralization reaction:-

The reaction between an acid & base to give a salt & water is called neutralization reaction.

• Acid + Base → salt + Water
  • HCl + NaOH → NaCl + H₂O
• Reaction of strong acid and strong base gives neutral salt.
• Reaction of strong acid and weak base gives acidic salt.
• Reaction of weak acid and strong base gives basic salt.

• Metallic oxides are basic in nature while non-metallic oxides are acidic in nature.

Reaction of metallic oxides with acids:-

• Metal oxide +Acid → Salt + Water
  • CuO + 2HCl → CuCl₂ + H₂O

Reaction of non-metallic oxides with bases:-

• Non-metallic oxide + Base → Salt + Water
  • CO₂ + Ca(OH)₂ → CaCO₃ + H₂O

Alkalies:-

Water soluble bases are called alkalies.
Ex:- NaOH, Mg(OH)₂ etc.

Dilution:-

The process of mixing an acid or base with water to decrease the
concentration of ions (H₃O⁺/OH^–) per unit volume is called dilution.

• The process of dissolving an acid or a base in water is highly exothermic.
• The acid must always be added slowly to water with constant stirring because if water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.

Acids in water:-

Acids in water give hydrogen (H⁺) ions, but they cannot exist alone. So, they combine with H₂O molecules to form H₃O⁺ ion.
HCl + H₂O → H₃O⁺ + Cl^–

Bases in water:-

Bases give hydroxide (OH^–) ions in water.
NaOH + H₂O → Na⁺ + OH^–

Strong Acid:- The acid which completely dissociates to give H⁺ ions is called strong acid. Ex:- HCl, HNO₃, H₂SO₄ etc.

Weak Acid:- The acid which dissociates partially to give H⁺ ions is called weak acid. Ex:- Acetic acid (CH₃COOH), Oxalic acid(C₂H₂O₄), Lactic acid(C₃H₆O₃) etc.

Strong Base:- The base which completely dissociates to give OH^– ions is called strong base. Ex:- KOH, NaOH etc.

Weak Base:- The base which partially dissociates to give OH^– ions is called weak base. Ex:- Ammonium hydroxide (NH₄OH), Zinc hydroxide [Zn(OH)₂] etc.

Universal Indicator:-

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

pH scale:-

• Value of pH = 7 ⇒ Neutral solution
• Value of pH < 7 ⇒ Acidic solution
• Value of pH > 7 ⇒ Basic solution

pH in everyday life:-

• Our body works in the pH range of 7.0 to 7.8.
• When pH of rain water is less than 5.6, it is called acid rain.
• Tooth decay starts when the pH of mouth is lower than 5.5.
  (Tooth enamel, made up of calcium phosphate is the hardest part of the body.)

Antacid:- The mild edible base which helps us to get relief from acidity by neutralizing the excess acid produced in the stomach is known as antacid.
Ex:- Milk of magnesia [Mg(OH)₂], baking soda [NaHCO₃], etc.

Common salt:-

• Chemical name:- Sodium Chloride
• Chemical formulae:- NaCl
• Preparation:- NaOH + HCl → NaCl + H₂O
• Uses of NaCl:-
  • It is used to add taste in food.
  • It is used to prepare sodium hydroxide, baking soda, washing soda, bleaching powder etc.

Rock salt:- The large crystals of solid salt found in earth’s crust are called rock salt. It is brown due to impurities.

Sodium hydroxide (NaOH):-

• Preparation:-
  • Chlor-alkali process:- When electricity is passed through an aqueous solution of NaCl (brine), it decomposes to form sodium hydroxide, hydrogen gas and chlorine gas. This process is called chlor-alkali process.
    2NaCl + 2H₂O → 2NaOH + H₂ + Cl₂
  • Chlorine gas is released at the anode, and hydrogen gas at the cathode. Sodium hydroxide solution is formed near the cathode.
• Uses of NaOH:-
  • It is used in de-greasing metals.
  • It is used in the preparation of soaps & detergents.
  • It is used in paper making industries.
  • It is used to prepare artificial fibres.
  • It is used to prepare bleach.
• Uses of Hydrogen:-
  • It is used as fuel.
  • It is used to prepare margarine.
  • It is used to prepare ammonia for fertilisers.
    • N₂ + 3H₂ → NH₃
• Uses of Chlorine:-
  • It is used for water treatment.
  • It is used in swimming pools to clean water.
  • It is used to prepare polyvinyl chloride (PVC).
  • It is used as disinfectant.
  • It is used to prepare chlorofluorocarbons (CFCs).
  • It is used to prepare pesticides.

Hydrochloric Acid (HCl):-

• Preparation:- H₂ + Cl₂ → 2HCl
• Uses of HCl:-
  • It is used to clean steel.
  • It is used in medicines.
  • It is used in cosmetics.
  • It is used to prepare ammonium chloride (NH₄Cl).
    NH₃ + HCl → NH₄Cl

Bleach:-

• Chemical Formula:- NaOCl
• Chemical Name:- Sodium oxychloride
• Preparation:- 2NaOH + Cl₂ → 2NaOCl + H₂
• Uses:-
  • It is used for household bleaches.
  • It is used for bleaching fabric.

Bleaching powder:-

• Chemical Formula:- CaOCl₂
• Chemical Name:- Calcium oxychloride
• Preparation;- Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
• Uses:-
  • It is used for bleaching cotton and linen in the textile industry.
  • It is used for bleaching wood pulp in paper factories.
  • It is used for bleaching washed clothes in laundry.
  • It is used as an oxidising agent in many chemical industries.
  • It is used for disinfecting drinking water to make it free of germs.

Baking Soda:-

• It is a mild edible non-corrosive base.
• Chemical Formula:- NaHCO₃
• Chemical Name:- Sodium bicarbonate
• Preparation:- NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃
• When NaHCO₃ is heated during cooking, following reaction takes place:
  2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
• Uses:-
  • It is used for making tasty and crispy pakoras.
  • It is used for faster cooking.
  • It is used as an antacid.
  • It is used in soda-acid fire extinguishers.
  • It is used for making for baking powder.

Baking Powder:-

• It is a mixture of baking soda and a mild edible acid such as tartaric acid.
• When baking powder is heated, following reaction takes place:
  NaHCO₃ + H⁺ → CO₂ + H₂O + Sodium salt of acid
  ex:- NaHCO₃ + CH₃CH₂COOH → CO₂ + H₂O + CH₃CH₂COONa
• Uses:-
  • CO₂ produced in this reaction is used for making bread and cake soft and spongy.

Washing Soda:-

• Chemical Formula:- Na₂CO₃.10H₂O
• Chemical Name:- Hydrated sodium carbonate
• Preparation;-
  2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
  Na₂CO₃ + 10H₂O → Na₂CO₃.10H₂O
• Uses:-
  • It is used in glass, soap and paper industries.
  • It is used in manufacturing of sodium compounds such as borax.
  • It is used as a cleaning agent for domestic purposes.
  • It is used for removing permanent hardness of water.

Water of crystallisation:-

It is the fixed number of water molecules present in 1 formula unit of a salt.
Ex:-

• Hydrated copper sulphate ⇒ CuSO₄.5H₂O
• Hydrated sodium carbonate ⇒ Na₂CO₃.10H₂O
• Hydrated calcium sulphate (Gypsum)⇒ CaSO₄.2H₂O

Plaster Of Paris:-

• Chemical Formula: CaSO₄.½H₂O
• Chemical Name:- Calcium sulphate hemihydrate
• Preparation:- On heating gypsum at 373 K, it loses water and becomes plaster of paris.
  CaSO₄.2H₂O → CaSO₄.½H₂O + 1½H₂O
• Uses:-
  • It is used for supporting fractured bones in right positions.
    When plaster of paris is mixed with water, it changes to gypsum which is a very hard substance.
    CaSO₄.½H₂O + 1½H₂O → CaSO₄.2H₂O
  • It is used for making toys, statues and decoration materials.
  • It is used for making surfaces smooth.