Acids, Bases and Salts – Class 10 Notes (NCERT)

Acids, Bases and Salts – Complete Class 10 Notes

NCERT based revision notes covering indicators, physical and chemical properties of acids and bases, pH scale, importance of pH in daily life, salts and common industrial chemicals.

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🧪Indicators & Colour Change

Indicators –

Indicate the presence of an acid or base in a solution by change in colour or odour when they are added.

(a) Natural indicator

found in plants e.g., Litmus paper , turmeric

(b) Synthetic indicator

man made e.g., Phenolphthalein, methyl orange etc.

(c) Olfactory indicator

substance whose odour or smell change in acidic or basic medium e.g., Vanilla, onion, clove.

Example of Acid – Base Indicators

S.No. Indicator Color change with Acid Colour change with Base
1. Turmeric No change To red
2. Methyl orange To red To yellow
3. Phenolphthalein No change To pink
4. Blue litmus solution To red No change
5. Red litmus solution No change To blue

Dilute Acid : Contains only a small amounts of acid and a large amount of water.

Concentrated Acid : A concentrated acid contains a large amount of acid and a small amount of water.

🥤Acids – Properties & Reactions

- Acids –

Physical properties:

  • Changes blue litmus to red.
  • Taste sour
  • All dilute acids conduct electricity.

Examples of Acids:

Acid Formula / Ionisation
Sulphuric acid H2SO4
Nitric acid HNO3
Hydrochloric acid HCl    HCl → H+ + Cl-
Carbonic acid CH3COOH    CH3COOH → H+ + CH3COO-
Note:
H+ ions are responsible for acidic nature of acids.

Chemical Properties of Acids and Bases

(i) Reactions with metals:

Dilute Acid + Metal → Salt + Hydrogen gas

2HCl + Zn → ZnCl2 + H2

2HNO3 + Zn → Zn (NO3)2 + H2

H2SO4 + Zn → ZnSO4 + H2

2CH3COOH + Zn → (CH3COO)2 Zn + H2

Pop test:

When a buring candle is brought near a test tube containing hydrogen gas it burns with a ‘Pop’ sound. This test is conducted for examining the presence of hydrogen gas.

Experiment:

• Take few pieces of Zn granules in a boiling tube and add about 5 ml of dil. H2SO4 acid to it.
• The delivery tube is caped in the test tube so that the evolved gas passes through the soap solution.
• Soap bubbles filled with the evolved gas come out of the solution.
• The flame of a lighted candle is brought in contact with the bubble.
• The gas in the bubble burns with a pop sound. This proves that the gas evolved in the reaction between zinc and sulphuric acid is hydrogen.

(ii) Action of Acids with metal Carbonates and metal bicarbonates (Metal hydrogen carbonate)

Test for CO2-

❑ Lime water Test : On passing the CO2 gas evolved through lime water (Ca(OH2)), it turns milky due to the formation of white precipitate of Calcium carbonate i.e., CaCO3.

If CO2 gas is passed continuously in excess, the white color disappeared due to the formation of soluble Ca(HCO3)2.

Note: Limestone, chalk and marble are different forms of calcium carbonate.

(iii) Reactions of metal oxides with acids:

Note :
(a) Appearance of blue green colour of the solution because of formation of CuCl2.
(b) Metallic oxides are said to be basic oxides because they give salt and water on reacting with acids.
🧴Bases – Properties

-Bases-

Properties of Bases:

  • (a) Bases have bitter taste.
  • (b) Base turn red litmus into blue.
  • (c) Bases are soapy to touch.
  • (d) Base conduct electricity in solution.
Base Chemical Formula & Ionisation
Sodium hydroxide NaOH    NaOH →Na+ + OH-
Potassium hydroxide KOH    KOH → K+ + OH-
Calcium hydroxide Ca(OH)2    Ca(OH)2 →Ca2+ + 2OH-
Magnesium hydroxide Mg(OH)2    Mg(OH)2 →Mg2+ + 2OH-
Aluminum hydroxide Al(OH)3    Al(OH)3 → Al3+ + 3OH-
Note:
OH- ions are responsible for basic nature of bases.

Chemical properties of Base:

(i) Reaction with metals
(ii) Reaction with non-metallic oxide

(i) Reaction with metals

(ii) Reaction with non-metallic oxide

Note :
Non Metallic oxides are said to be acidic in nature because on reacting with a base they produce Salt and Water.
🔍Common properties of acids

WHAT DO ALL ACIDS HAVE IN COMMON?

  • All acids have similar chemical properties.
  • All compounds containing hydrogen are not acidic e.g., Glucose, C6H12O6 and alcohol (C2H5OH) solutions.
  • The apparatus is set as shown in figure.
  • Solutions, of glucose is added and the switch is turned on. The bulb does not glow. This means glucose does not dissociate into ions on dissociation. So, glucose is not an acid. Similarly alcohol is also not an acid.
  • But in case of Acids , the bulb will start glowing. This suggests that, all acids produce hydrogen ions (H+) which are responsible for acidic properties.
  • H+ ion does not exist without water so, we should write H+(aq) or H3O+ (Hydronium ion).
💧Common properties of bases

WHAT DO ALL BASES HAVE IN COMMON?

  • Bases gives hydroxide (OH–) ions in water.
  • Bases which are soluble in water are called alkalis.
⚖️Neutralisation & Dilution

-Acid + Base -

  • Acids react with bases to produce Salts and water. This type of reaction is called Neutralization reaction.
  • In this reaction, an acid neutralizes or reduces the effect of a base or vice -versa.

Dissolution of Acid or Bases

  • The process of dissolving an acid or a base in water is a highly exothermic . Care must be taken.
  • If water is added to the concentrated acid, the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.
  • So, The acid must always be added slowly to water with constant stirring.
  • Mixing an acid or base with water results in decrease in the concentration of ions (H3O+/OH–) per unit volume. Such a process is called dilution and the acid or the base is said to be diluted.
📊pH Scale & Universal Indicator

Universal indicator:

It is a mixture of several indicator, which shows different colours at different concentration of H+ (aq) ions in solution.

- Strength of an Acid or Base-

  • Strength of acids and bases depends on the no. of H+ ions and OH–ions produced respectively. With the help of a universal indicator we can find the strength of an acid or base.
  • This indicator is called pH scale.
  • pH scale: the scale for measuring H+ concentration in a solution is called pH scale.
  • pH = Potenz in German means power.
  • This scale have values measuring from 0 (very acidic) to 14 (very basic/alkaline) and 7 Neutral (water in Neutral).
  • Higher the H+ ion concentration, lower is the pH value.

If pH < 7 = Acidic solution
If pH = 7 = Neutral solution
If pH > 7 = Basic solution

⭐Extra Facts & Types

- Boost your knowledge -

The aqueous solution of glucose (C6H12O6) and alcohol (C2H5OH) does not show acidic characters because their Hydrogen do not separate out as H+ ions on dissolving in water. therefore, all acids contain H+ ions but all the Hydrogen containing compounds are not acids.

Types of Acids and Bases (Based on their strengths)

Types of acids:

(a) strong Acids are completely ionizes to give more H+ ions. e.g. HCl, H2SO4 and HNO3.

(b) Weak Acids which are partially ionized in water and hence it produces small amount of H+ ions e.g. CH3COOH, H2CO3 (Carbonic acid)

Types of Base:

(a) Strong Bases – Strong bases completely ionizes to give more OH– ions in the solution. e.g., NaOH, KOH, Ca(OH)2

(b) Weak Bases : these are partially ionized in water and hence it produces small amount of OH- ions in the solution. e.g., NH4OH

🌍Importance of pH in our daily life

Importance of pH in our daily life

(a) Importance of pH in our digestive system – pH level of our body regulates our digestive system. In case of indigestion our stomach produces acid in a very large quantity because of which we feel pain and irritation in our stomach. To get relief from this pain antacids are used. These antacids neutralizes the excess acid and we get relief.

(b) pH of Acid Rain : When pH of rain water is less than 5.6 it is called Acid Rain. When this acidic rain flows into rivers it lowers the pH of river water and this water becomes acidic, which causes a threat to the survival of aquatic life.

(c) pH of Soil : Plants require a specific range of pH for their healthy growth. If pH of soil of any particular place is less or more than normal than the farmers add suitable fertilizers to it.

(d) Our body functions works between the range of 7.0 to 7.8. Living organisms can survive only in the narrow range of pH change.

(e) Tooth decay and pH : Tooth enamel is the hardest substance in the body which made up of Calcium phosphate. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth. Using toothpaste which is generally basic can neutralize the excess acid and prevent tooth decay.

(f) Bee sting or Nettle sting contains methanoic acid which causes pain and irritation. When we apply a weak (mild) base like baking soda on it we get relief.

🍋Natural Acids

Some naturally occurring acids:

Source Acid
Vinegar Acetic acid
Orange, lemon Citric acid
Tamarind Tartaric acid
Tomato Oxalic acid
Curd Lactic acid
Ant/Bee/Nettle sting Mehanoic acid
🧂Salts & their Properties

Salts

∎ A salts is a compound formed from an acid by replacement of the Hydrogen in the acid by a metal.
∎ Salts are also formed when acids react wit bases.

Characteristics of salts:

  • Salts are mostly solid.
  • They have high melting point and boiling points.
  • They are usually soluble in water.
  • Salts are ionic compounds which consist of cation and anions.

Family of salts

S.No. Name of salts formulae Acid and Base
1. Potassium sulphate K2SO4
2. Calcium sulphate CaSO4
3. Sodium chloride NaCl
4. Aluminum chloride AlCl3
5. Sodium nitrate NaNO3
6. Sodium carbonate Na2CO3

pH of salt solutions:

Neutral Salts
Strong Acid + Strong base
pH value is 7
e.g., NaCl, CaSO4

Acidic Salts
Strong Acid + weak base
pH value is less than 7
e.g., NH4Cl, NH4 NO3

Basic Salts
Strong base + weak acid
pH value is more than 7
e.g., CaCO3, CH3COONa

🏭Important Industrial Salts

Salts and its formation:

(1) Common salt
(2) Caustic Soda (NaOH)
(3) Bleaching powder
(4) Baking soda
(5) Washing Soda
(6) Plaster of paris

(1) Common salt

Chemical name : Sodium chloride
Chemical formula: NaCl

Preparation:

Common salt is obtained from sea water by the process of evaporation and underground deposit (Rock salt).

Uses:

  • it is used as raw material for making a large number of useful chemicals in the industries such as NaOH (Caustic soda), Na2CO3 (Washing soda), NaHCO3 (Baking soda), etc.
  • It is used in cooking food and it improve the flavor of food.
  • It is used as preservatives (Pickles)
  • It is used in the manufacturing of soap.
  • It is used to melt ice which is collected on the road during extreme winter in cold countries.

(2) Caustic Soda (NaOH):

Chemical name: Sodium hydroxide
Chemical formula: NaOH

Preparation:

  • Prepared by the method called chlor-alkali.
  • When aqueous solution of sodium chloride (Brine solution) is passed through electricity, it decomposes to form sodium hydroxide. This process is also known as Chlor-alkali process.

(3 )Bleaching powder

• Chemical name: CaOCl2
• Chemical formula: Calcium oxy chloride

Preparation:

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

Use of Bleaching powder –

  • (i) for bleaching cotton and linen in the textile industry, for bleaching wood pulp in paper factories and for bleaching washed clothes in laundry;
  • (ii) as an oxidising agent in many chemical industries; and
  • (iii) for disinfecting drinking water to make it free of germs.
  • (iv) Making wool unshrinkable.

(4) Baking soda

• It is used in kitchen for making pakoras, toast and for faster cooking.
Chemical name: Sodium hydrogen carbonate
Chemical formula: NaHCO3

Preparation:

Uses:

  • For making baking powder, which as mixture of soda and tartaric acid. When baking powder is mixed with water, following reaction takes place.
  • On heating, baking soda generate bubbles of carbon dioxide (leaving holes in cakes or pastries and making them light and fluffy).
  • It is used as an antacid to remove acidity of stomach.
  • It is used in making baking powder.
  • It is also used in fire- extinguisher.

(5) Washing Soda:

Chemical name: Sodium carbonate Decahydrate
Chemical formula: Na2CO3.10H2O

Preparation:

Step: 1

Step: 2

Step: 3

Uses of washing soda

  • (i) Sodium carbonate (washing soda) is used in glass, soap and paper industries.
  • (ii) It is used in the manufacture of sodium compounds such as borax.
  • (iii) Sodium carbonate can be used as a cleaning agent for domestic purposes.
  • (iv) It is used for removing permanent hardness of water.

Imp. point

Water of crystallization : Fixed number of water molecules (H2O) present in one formula unit of a salt.

For example: Copper sulphate crystals (CuSO4.5H2O). these crystals are blue in colour which seems to be dry contain water of crystallization. On heating copper sulphate crystals water droplets appear and when this water is completely removed it appears white in color.

Crystal again moistened with water, they turns blue in color.so the formula of hydrated copper sulphate – CuSO4. 5H2O.

(6) Plaster of Paris

• On heating gypsum at 373 K, it loses water molecules and becomes calcium sulphate hemihydrate . This is called Plaster of Paris (POP).

Preparation:

 It is obtained when gypsum, , is heated to 393 K.

• On mixing water, it again change to Gypsum giving hard solid mass e.g., CaSO4.2H2O.

• The temperature during the heating of Gypsum should not be exceeds above 1000C because if it happens then the water present in it completely evaporated and form anhydrous (CaSO4) which is called dead burnt plaster which is of no use.

Use:

  • It is used in making moulds for pottery and ceramics etc.
  • In hospitals, it is use as plaster for supporting fractured bones in the right position.
  • It is also use in making models, decorative materials and black board chalk.
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