Download PDF class 10 science chapter 2 notes

class 10 science chapter 2 notes pdf: In which we will discuss the presentation of H⁺ and OH⁻ ions in terms of their definition, general properties, examples and uses, the concept of PH scale, the importance of PH scale in everyday life, sodium hydroxide, bleaching powder, baking soda, washing soda and plaster of Paris, etc.

class 10 science chapter 2 notes

Definition of Acid:

Acid is called acid in the English language, the word acid is derived from the Latin word 'acids', which means sour. So we can say that substances that are sour in taste are acids.

Properties of Acid:-

Physical properties of acids:-

  • Are sour in taste.
  • Turns blue litmus red.
  • Gives H+ ions in an aqueous solution.
  • To conduct electric current in an aqueous solution.

Chemical properties of acids:-

  • Reacting with metal to remove H₂.

  • Reacting with metal carbonate/hydrogen carbonate to release CO₂.

  • Some metal oxides react with acids to form salts and water.

️ Natural sources of acid:-

  • Lime (Citric Acid)
  • Tomato (Ascorbic Acid)
  • Grapes (tartaric acid)
  • Vinegar (acetic acid)
  • milk (lactic acid)
  • Tamarind (tartaric acid)
  • Apple (Malic Acid)


Types of Acids:-

  • strong acid
  • weak acid
  • concentrated acid
  • dilute acid

Strong Acid:-

Those acids which completely ionize in aqueous solution are called strong acids. Examples of strong acids are sulfuric acid (H₂SO₄), hydrochloric acid (HCI), nitric acid (HNO₃), hydrobromic acid, etc.

Strong acids have a high ability to give up protons i.e. hydrogen ions (H + ) i.e. strong acids dissociate into ions of their constituent elements.

Weak acid:-

Acids, which are partially ionized but not completely ionized in an aqueous solution are called weak acids. Examples of weak acids are acetic acid (CH₃COQH), formic acid (HCOOH), hydrogen sulfide (H₂S), etc.

Weak acids do not completely give up their hydrogen ions (H+). At the same concentration, weak acids have a higher pH than strong acids.

Concentrated Acid:-

In which acid is present in large quantities, whereas water is in small quantities.

Dilute Acid:-

In which acid is present in small quantities, whereas water is present in large quantities.

️ Alkaline:-

Substances whose taste is bitter and which feel like soap when touched. are called bases.

️ class 10 science chapter 2 notes: Properties of base

Physical properties of alkali:-

  • It is bitter in taste.
  • Turns red litmus blue.
  • Gives OH- ion in an aqueous solution.
  • Do not conduct electric current in an aqueous solution.

Chemical properties of alkali:-

  • Reacts with alkali metals to liberate H₂.
  • Alkali reacts with an acidic oxide to form a salt.



Indicators show the presence of an acid or a base in a given solution. Their color or smell changes in acidic or basic medium.

️ Types of pointer:-

Well, there are many types of detectors. But their common types are as follows:-

️ 1. Natural indicator:-

Those indicators which are obtained from natural sources are called natural indicators. For Examples- Litmus, Red cabbage juice, Turmeric, Hydrangea flower juice, etc.


  • The most commonly used natural indicator for the identification of acids and bases is litmus.
  • Litmus is obtained from lichens (algae).

Litmus paper:-

  • Litmus is available in the form of solution and in the form of strips of paper, these paper strips are called litmus paper.
  • Litmus paper is of two colors blue and red, acid turns blue litmus paper red while alkali turns red litmus paper blue.


  • Turmeric is also another type of natural indicator.

  • It is yellow in color.

  • Many times you must have seen that when a white cloth gets a vegetable stain and when it is washed with soap (alkaline nature), it turns the stain of that stain brown-red.

  • There is no change in the color of turmeric with acid.

  • Its color becomes brownish-red with alkali.

2. Synthesized indicator:-

These are those indicators that are not natural but are made by chemical substances.

Eg:- Methyl orange and phenolphthalein etc.

They are used to test for acids and bases.

️ 3. Aromatic indicator:-

There are some substances whose odor changes in acidic or basic medium, such substances are called odorous indicators. Eg:- Onion and clove and oil etc.

️ 4. Universal indicator:-

A universal indicator is a mixture of different chemicals that tell about a substance with different pH by changing its color whether it is a base or an acid.

class 10 science chapter 2 notes - Salt

Metals displace hydrogen atoms from acids in the form of hydrogen gas and form a compound called salt.

Properties of salt:-

  • Salts are found in the solid state.

  • Generally, salts are neutral.

  • Aqueous solutions of salts are good conductors of electricity.

Pop Test:-

When a burning candle is brought near a test tube containing hydrogen gas, the sound of pop is produced. This test is used to show the presence of hydrogen.

️ The reaction of acid and base with metal:-

The reaction of metal with acid:-

Acid + Metal → Salt + Hydrogen

2HCl + Zn → ZnCl₂ + H₂

The reaction of metal with base:-

Alkali + Metal → Salt + Hydrogen

2NaOH + Zn → Na₂ZnO₂ + H₂



Such substances which do not change the color of red or blue litmus paper are called neutral.

Such substances are neither acidic nor basic.

Such as - salt, salt, calcium chloride, sodium carbonate, sodium bicarbonate, etc.

️ Neutralization Reaction:-

When the observed effect of the base by acid and effect of acid by the base is over and as a result salt and water are obtained, a neutralization reaction takes place.


  • NaOH (aq) + HCl (aq) → NaCl (aq) + H₂O (l)

  • Strong Acid + Weak Base → Acidic Salt + Water [pH of solution less than 7]

  • Weak acid + strong base → alkaline salt + water [pH of a solution greater than 7]

  • Strong acid + strong base → neutral salt + water [pH of solution = 7]

  • Weak acid + weak base → neutral salt + water [pH 7 of solution]

️ The reaction of metallic oxides with acids:-

Metallic oxide + acid → salt + water

CaO + 2HCl → CaCl₂ + H₂O

Metallic oxides have a basic nature. Because they react with acids to form salts and water.

Example:- Cuo, Mgo

Similarities between acids and bases:-

All acids produce H⁺ ions.

All bases produce OH⁻ ions.

What happens to an acid or a base in an aqueous solution?

On adding an acid or a base to water, the concentration of the ion (H₃O⁺ or OH⁻) decreases per unit volume. This process is called dilution and acids or bases are diluted.

️ Strength of base and acid:-

The strength of a base or acid depends on the number of H+ ions or OH- ions produced by it.

We can determine the strength of an acid or a base by a universal indicator.

️ Universal Indicator:-

There is a mixture of several indicators.

These indicators show different concentrations of hydrogen ions in a solution in different colors.

️ pH scale:-

A scale was developed to find the concentration of H⁺ ion present in a solution called pH scale.

The p in pH is 'Pusenz' (Potenz) which is a German word, which means power. If:-

  •  PH = 7 → neutral solution

  •  PH < 7 → Acidic solution

  •  PH > 7 → alkaline solution

️ Importance of pH in daily life:-

Plants and animals are sensitive to pH. ,

Our body works between the 7.0 to 7.8 pH range.

class 10 science chapter 2 notes pdf : Soil pH:-

Plants require a specific pH range for good yield. If the pH of the soil of a place is low or high, then farmers add acidic or alkaline substances to it as needed.

the pH of our digestive system:-

Our stomach produces hydrochloric acid (HCI) which aids in the digestion of food.

In the case of dyspepsia, the stomach produces acid in excess, due to which pain and burning are experienced in the abdomen.

To get rid of this pain, bases like antacids are used which neutralize the excess amount of acid. eg (milk of magnesia)

Tooth decay due to pH change:-

  • Tooth decay starts when the pH of the mouth is less than 5.5.

  • Tooth enamel is made up of calcium phosphate, which is the hardest substance in the body, it does not dissolve in water but becomes corrosive when the pH of the mouth is less than 5.5.

  • The excess amount of acid can be neutralized by using alkaline toothpaste.

Self-defense from chemicals produced by animals and plants:-

  • The sting of a bee releases an acid due to which pain and burning are experienced. The use of baking soda in the stung limb provides relief.

  • Nettle sting hairs release methanoic acid, due to which burning pain is experienced. It is treated by dyeing the leaves of the dock plant at the site of the sting.

️ Acid rain:-

When the pH value of rainwater falls below 5.6, it is called acid rain.

️ pH of salts:-

  • The pH of the salts of strong acid and strong base is 7 and they are neutral.

  • Whereas salts of strong acid and weak base have pH values less than 7 and are acidic.

  • Salts of strong bases and weak acids have a pH of more than 7 and are basic.

️ Chemicals from common salt:-

Sodium Chloride NaCl is called common salt which we use in food.

It is made from seawater.

Rock salt is a substance found in the form of brown crystals. It is obtained by extraction like coal.

  • ️ Common salt - the raw material of chemicals:-

Common salt thus obtained contains many substances of our daily use; Eg :- Sodium hydroxide is an important raw material for baking soda, washing soda, bleaching powder, etc.

1. Sodium Hydroxide (NaOH):-

On passing electricity through an aqueous solution of sodium chloride (salt water), it dissociates to form sodium hydroxide. This process is called Chlor-alkali process because the products produced are chlorine (chlor) and sodium hydroxide (alkali).

2NaCl (aq) + 2H₂O(l) → 2NaOH (aq) + Cl₂(g) + H₂( g )

Chlorine gas is liberated at the anode and hydrogen gas is liberated at the cathode. Sodium hydroxide solution is also formed at the cathode. All the three products produced by this process are useful.

️ 2. Bleaching powder:-

Bleaching powder is formed by the action of chlorine on dry slaked lime [Ca(OH)₂].

   Ca(OH)₂ + Cl₂ → CaOCI₂ + H2O

Use of bleaching powder:-

  • For bleaching of cotton and linen in the textile industry.

  • For bleaching wood marrow in a paper factory.

  • As an auxiliary in chemical industries.

  • As a disinfectant to make drinking water free from bacteria.

️ 3. Baking Soda:-

Baking soda is commonly used in the kitchen to make delicious crispy pakodas etc. Sometimes it is also used for quick cooking of food.

The chemical name of this compound is sodium hydrogen carbonate (NaHCO₃). Sodium chloride is used as a basic substance in its preparation.

Use of Baking Soda:-

  • Baking powder is a mixture of (baking soda + tartaric acid).

  • The CO₂ produced by this reaction causes the leavening of the bread or cake, making it soft and spongy.

  •  It is a component of antacids.

  • It is also used in soda-acid fire extinguishers.

️ 4. Washing soda ( Na₂CO310H₂O ) :-

Re-crystallization of sodium carbonate gives washing soda. It is a basic salt.

Na₂Co₃ + 10H₂0 → Na₂CO₃ 10H₂0

Use of washing soda:-

  • It is used in the glass, soap, and paper industries.

  • It is used in the production of borax.

  • It is used for cleaning homes.

  • It is used to remove the permanent hardness of water.

️ 5. Plaster of Paris CaSO₄1/2H₂0 :-

plaster of Paris ka sutra : CaSO₄(1/2H₂0)

When gypsum is heated to 373K, it gives up water molecules to form calcium sulfate hemihydrate (POP).

It is a white powder, which when mixed with water, it again becomes gypsum and provides solid.

USE of plaster of Paris class 10-

  • Plaster of Paris is used by doctors to fix broken bones in the right place.

  • It is used to make toys, to make decorations.

  • It is used to make the surface smooth.

the water of crystallization class 10

The number of water molecules in a formula unit of salt is called water of crystallization.


  •  Cuso₄.5H₂0 has 5 molecules of water for crystallization.

  • Na₂CO₃. There are 10 molecules of water of crystallization in 10H₂0.

  • There are 2 molecules of water of crystallization in Caso₄.2H₂O.


Here we add all topics related to class 10 science chapter 2 notes and all formulas like (the plaster of Paris formula) and many more.

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