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.

image_printPrint

Comments

The maximum upload file size: 100 MB. You can upload: image. Drop file here