Class 10 Science Chapter 2 Acids, Bases and Salts Notes

10 Class Science Chapter 2 Acids, Bases and Salts Notes

TextbookNCERT
ClassClass 10
SubjectScience
Chapter Chapter 2
Chapter NameAcids, Bases and Salts
CategoryClass 10 Science Notes
MediumHindi

Class 10 Science Chapter 2 Acids, Bases and Salts Notes. here In which we will discuss about the presentation of H+ and OH ions in terms of their definition, general properties, examples and uses, concept of PH scale, 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 Acids, Bases and Salts Notes

📚 Chapter = 2 📚
💠 Acids, Bases and Salts💠

❇️ ACIDS :-

🔹 The term ‘acid has been derived from the Latin word, acidus, which means sour.

🔹 Acids are those chemical substances which have a sour taste and turn blue litmus solution red. 

🔹 According to Arrhenius concept, substances that furnish H⁺ ions in an aqueous solution are called acids. Example :- H₂SO₄ → 2H⁺  + SO₄²⁻

❇️ Properties of Acids :-

🔶 Physical Properties of Acids :-

  • Sour in taste. 
  • Change the colour of blue litmus to red.
  • Acid solution conducts electricity.
  • Give H⁺ ions in aqueous solution. 

🔶 Chemical Properties of Acids :-

  • Reacts with metals to liberate hydrogen.  
  • Reacts with metal carbonates/metal hydrogen carbonate to liberate CO₂
  • Reacts with certain metal oxides to form salt and water.

❇️ Natural sources of Acid :-

Substance that contain acidsOrganic acid present in them
1. Orange, lemonCitric acid, ascorbic acid (vitamin C) 
2. Apple Malic acid
3. Tamarind (imli),grapeTartaric acid
4. Olive oil Oleic acid
5. VinegarAcetic acid
6. Curd (sour milk)Lactic acid
7. Urine Uric acid 
8. TomatoOxalic acid
9. Tea Tannic acid 
10. Red antsFormic acid
11. Green leafy vegetables Folic acid
12. Gastric juiceHydrochloric acid
13. AmlaAscorbic acid 
14. SpinachOxalic acid
15. Bees and nettle stingFormic acid
16. Rancid butterButyric acid

❇️ Types of Acid :-

🔹 On the basis of their source/occurence acids are of two types – 

  • (1) Mineral acids 
  • (2) Organic acids

🔶 Mineral Acids :-

🔹 Acids that are obtained from rocks and minerals are known as mineral acids. e.g., HCl, HNO, 

🔹 Some of the commonly used mineral acid along their uses are given below as :-

NameType of acidChemical Formula Uses
Hydrochloric acid Mineral AcidHCI Purification of NACl to make aqua regia mixture of Hu₂HNO₃ in ratio of 3 : 1, bleaching agent
Phosphoric acid Mineral AcidH₃PO₄ In fertilizers and in antirust paints.
Carbonic acidMineral AcidH₂CO₃Used in tanning industry, in soft drinks etc.
Sulphuric acid Mineral AcidH₂SO₄Used in car batteries, in paints, plastics, drugs, in petroleum refining.
Nitric acidMineral AcidHNO₃Used in explosives manufacture like TNT and fertilizers, refining of gold and silver.

🔶 Organic Acids :-

🔹 Acids that are present in animals and plants are called as organic acids. e.g., Lactic acid, Formic acid.

🔹 Some of commonly used organic acids along their chemical formula with their uses are given as :-

NameType of acidChemical Formula Uses
Lactic acidOrganic AcidCH₃CH(OH)COOHFlavouring agent and food preservative. 
Organic AcidOrganic AcidC₆H₅COOHUsed in dyes, perfumes and insect repellents, food preservative.
Benzoic acidOrganic AcidCH₃COOHUsed as a solvent in the manufacture of dyes and perfumes, in vinegar, production of plastics. 
Organic AcidOrganic AcidHCOOHIn tanning leather, in medicines for treating disease like gout of joints.
Citric acidOrganic AcidC₆H₈O₇Flavouring and preserving agent in soft drink and toffees.

🔶 Strong Acids :- These acids ionise more or less completely when dissolved in water, e.g., sulphuric acid (H₂SO₄) nitric acid (HNO₃) and hydrochloric acid (HCl).

🔶 Weak Acids :- These acids ionise to a small extent when dissolved in water, e.g., acetic acid (CH₃COOH), formic acid (HCOOH) and carbonic acid (H₂CO₃).

❇️ Chemical Properties of Acids :-

🔶 Reaction with Metals :- Dilute acids (e.g. HCl and H₂SO₄ not HNO₃) react with certain active metals like zinc (Zn), iron (Fe), etc., to evolve H₂ gas. e.g. :-

Zn(s) + H₂SO₄(aq) → ZnSO₄(aq)+ H₂(g ) 

🔶 Reaction with Metal Oxides :- Acids react with certain metal oxides (basic oxides) to form salt and water. e.g :- 

CaO(s) + 2HCI(aq) → CaCl₂(aq)+ H₂O(l) 

🔶 Reaction with Metal Carbonate and Hydrogen Carbonate :- Acids react with metal carbonates and hydrogen carbonates to produce carbon dioxide gas. e.g :-

  • CACO₃(s) + 2HCl(aq)→CaCl₂(aq) + H₂O(l) + CO₂(g )
  • NaHCO₃(s) + HCL(aq) → NaCl (aq) + H₂O(s) + CO₂(g)

❇️ Bases :-

🔹 Substances that furnish hydroxide ions (OH⁻ ) in aqueous solution are called bases. e.g.

🔹 Bases are chemical compounds which have bitter taste, are soapy and slippery to touch, and turn red litmus solution blue, e.g., sodium hydroxide, potassium hydroxide, aluminium hydroxide, etc.

❇️ Properties of Bases :-

🔶 Physical Properties of Bases :-

  • Bitter in taste 
  • Turn red litmus blue 
  • Give OH⁻ ions in aqueous solution 
  • Does not conduct electricity in aqueous sol”

🔶 Chemical Properties of Bases :- 

  • Alkali reacts with metal to liberate H₂
  • Bases reacts with acidic oxides to form water.

❇️ Types of BASES :-

🔶 Strong Bases :- The substances/bases which ionise completely to furnish OH⁻ ions are called strong bases. e.g. KOH (caustic potash). 

🔶 Weak Bases :- The bases which ionise only partially are called weak bases. e.g. Calcium hydroxide [Ca(OH)₂]. 

🔶 Alkali Water :- soluble base is called alkali. e.g. NaOH. All alkalies are base, but all base are not alkalies.

❇️ Chemical Properties of Bases :-

🔶 Reaction with Metals :- Strong bases react with active metals to produce hydrogen gas. e.g. :- Zn(s)+ 2NAOH(aq) → Na₂Zno₂(aq) + H₂(g)

🔶 Reaction with Non-metallic Oxide :- Bases react with non-metallic oxides (acidic oxides) to produce salt and water. This reaction proves that non-metallic oxides are acidic in nature. e.g. :- CO₂(g) + Ca(OH)₂(aq) → CaCO₃(s)+ H₂O(l)

🔶 Reaction Between Acids and Bases :-

🔹 Acids react with bases to produce salt and water. In this reaction, acid neutralises a base, i.e. reduce its effect or vice-versa, thus the reaction is known as neutralisation reaction.  

🔹 In general, neutralisation reaction can be written as Base + Acid → Salt +Water

 🔹 e.g. :- NaOH(aq) + HCI(aq) → NaCl(aq) + H₂O(l)

❇️ What do all Acids and Bases have in common :-

  • All acids have H+ ions in common. 
  • Acids produce H+ ions in solution which are responsible for their acidic properties. 
  • All bases have OH- (hydroxyl ions) in common.

❇️ Indicators :-

🔹 Indicators are the substances that change their colour or odour when added into an acid or alkaline solution.

❇️ Classification of Indicators :-

🔹 Indicators can be classified as natural, synthetic indicators, olfactory indicators and universal indicators. 

❇️ Natural Indicators :-

🔹 These indicators are found in nature in the plants. e.g. Litmus solution is a purple colour dye extracted from the lichen plant. 

🔶 Litmus :- It is a natural dye made from small plants called lichens (a plant belong to division Thallophyta).Litmus solution is a purple dye that is used as an indicator. Blue and red litmus solutions are prepared from two different varieties of lichens. 

🔶 Litmus paper :- Blue or red litmus paper is made by dipping a strip of filter paper in blue or red litmus solutions. The paper is then removed from the solution and then dried up. Blue litmus paper will turn red in an acidic solution and red litmus paper will turn blue in a basic solution.

❇️ Synthetic Indicators :-

🔹 The indicators which are synthesised in the laboratory or industry are known as synthetic indicators. e.g. Methyl orange, phenolphthalein.

🔶 Methyl orange :- Solid methyl orange in very little amount is dissolved in hot water and then filtered. The filtrate is used as methyl orange that will turn red in acidic solutions and yellow in basic solutions.

🔶 Phenolphthalein :- An alcoholic solution of phenolphthalein is used as an indicator. It become colourless in an acidic solution, but it will become pink (red) in basic solution.

❇️ Olfactory Indicators :-

🔹 Those substances whose odour changes in acidic or basic medium are called olfactory indicators. e.g. Vanilla extract and onion.

❇️ Universal Indicators :-

🔹 To judge how strong a given acid or base is, a universal indicator is used which is a mixture of several indicators. It shows different colours at different concentrations of hydrogen ion in a solution.

❇️ Strength of an Acid or Base :- 

🔹 Strength of an acid or base depends on the number of H+ ions or OH- ions produced by them respectively.

🔹 Larger the number of H+ ions produced by an acid, stronger is the acid. Similarly, larger the number of the OH- ions produced by a base, stronger is the base.

❇️ PH Scale :-

🔹 A scale that is used measuring the strength of acids and bases in a solution is known pH scale. It has been developed by S.P.L. sorensen. The P in pH stands for ‘potenz’ in German meaning power and ‘H’ stands for hydrogen ions. 

🔹 The acidity or basicity of a solution is usually expressed in terms of a function of the H⁺ ion concentration. This function is called the pH of a solution. 

  • pH should be thought of simply as a number that indicates the acidic or basic strength of solution. 
  • On the pH scale we can measure pH from 0 (very acidic) to 14 (very alkaline). 
  • Higher the H⁺ ion concentration, Lower will be value of the pH scale. 

🔹 The pH of an aqueous solution is the negative logarithm of its H ion concentration. That is, 

  • pH = -log [H⁺].
  • pOH = -log [OH-] 

🔶 Characteristic of pH scale are :- 

  • For acidic solution, pH < 7 
  • For alkaline solution, pH > 7 
  • neutral solution, pH = 7

❇️ Importance of pH in everyday :-

🔶 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.

🔶 pH of the soil :-

  • Plants require a specific pH range for their healthy growth.

🔶 pH in our digestive system :-

  • Our stomach produces HCl acid which helps in digestion. 
  • During indigestion, stomach produces more acid and cause pain and irritation. 
  • To get rid of this pain, people uses antacid (mild base) like milk of magnesia [Mg(OH)₂] to neutralize excess acid.

🔶 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.

🔶 Self defence by animals and plants through chemical warfare :-

  • Bee sting leaves an acid which cause pain and irritation. Use of a mild base like baking soda on stung area gives relief. 
  • Stinging hair of nettle leaves inject methanoic acid causing burning Sensation or pain. Rubbing with leaf of dock plant give relief.

❇️ Salt :-

🔹 A salt is a compound that is formed by the reaction of an acid with a base in which the hydrogen of the acid is replaced by the metal. 

H₂SO₄ + NaOH → NaHSO₄ + H₂O 

🔹 This type of reaction is known as neutralisation reaction.

❇️ Different Types of Salts :-

🔹 The different types of salts are: normal salt, acid salt, basic salt and double salt. 

🔶 Normal salt :- A salt which does not contain any replaceable H atoms or hydroxyl groups Examples :- CaSO₄, K₃PO₄, Na₂SO₄

🔶 Acidic salt :- When a polybasic acid is not completely neutralized by a base, the salt formed will contain replaceable H atoms. A salt that contains replaceable hydrogen atoms is called an acidic salt. 

  • H₂SO₄ + NaOH → NaHSO₄ + H₂O 
  • NaHSO₄ + NaOH → Na₂SO₄ + H₂0
  • Examples :- NaHSO₄, KHCO₃ and KH₂PO, are examples of acidic salts. 

🔶 Basic salt :- When these salts are the product of incomplete neutralization of strong base and weak acid, the salt produced contain hydroxyl group(s) (OH) also. Such a salt is known a basic salt. Example :- 2P6CO₃.Pb(OH), Br(OH)₂NO₃ 

Bi(OH)₃ + HNO₃ → Bi(OH)₂NO₃ + H₂O 

🔶 Double salt :- In a double salt, there are two different negative ions and/or positive ions are present. For example, Hence, it is a double salt. Example :- Potash alum, K₂SO₄.Al₂(SO₄)₃ .24H₂0, also is a double salt

❇️ Classification of Salts Based on pH Values :-

🔶 Neutral salt solutions :- Salt solutions of strong acids and strong bases that are neutral in nature and they have pH value equal to 7. They do not change the colour of litmus solution. For Example :- NaCl, NaNO₃, Na₂SO₄ etc.

🔶 Acidic salt solutions :- It is salt solutions of strong acids and weak bases that are of acidic nature and they have pH value less than 7. They change the colour of blue litmus solution to red. For Example :- (NH₄)₂SO₄, NH₄Cl etc. 

  • In both these salts, the base NH₄OH is weak while the acids H₂SO₄ and HCl are strong. 

🔶 Basic salt solutions :- Salt solutions of strong bases and weak acids that are of basic nature and they have pH value more than 7. They change the colour of red litmus solution to blue. For Example :- K₃PO₄, Na₂CO₃ etc.

❇️ Sodium Chloride (NaCI) – Common Salt :- 

  • Sodium chloride (NaCl) also known as common salt or table salt. It is the most important part of our diet. 
  • It is produced by the reaction between of sodium hydroxide (NaOH) and hydrochloric acid (HCl) solutions. 
  • It is separated by some suitable methods. 
  • Deposits of the salts that are found in different part of the world and is called as rock salt. When salt is pure, it is white in colour & crystalline solid. However, it is often brown in colour due to the presence of impurities in it. 

❇️ Uses of NaCI :-

🔶 Raw material for chemical :- Sodium chloride is also a very useful raw material for different chemicals. Like for hydrochloric acid (HCl), washing soda (Na,CO,.10H,0), baking soda (NaHCO,). 

🔶 Essential for life :- Sodium chloride is quite important for life. Biologically, NaCl has a number of functions to perform such as in muscle contraction, in conduction of nerve impulse in the nervous system and it is also converted in HCl that helps in the digestion of food in the stomach. 

❇️ Sodium Hydroxide (NAOH) :-

🔹 NaOH is chemically known as Caustic Soda. When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. The process is known as the chlor-alkali process because of the products formed-chlor for chlorine and alkali for sodium hydroxide.  

  • 2NACl(aq) + 2H₂O(l) ( Electric current →) 2NAOH(aq)+ Cl₂(g) + H₂(g) 
  • Chlorine gas is released at the anode. 
  • Hydrogen gas is released at the cathode.
  • Sodium hydroxide solution is formed near the cathode.

❇️ Chemicals from Common Salt (NaCl) :-

  • Sodium Hydroxide (NaOH)
  • Bleaching Powder (CaOCl₂)
  • Baking Soda (NaHCO₃)
  • Washing Soda (Na₂CO₃.10H₂0)
  • Plaster of Paris (CaSO₄.½H₂0)

❇️ Sodium Hydroxide (NaOH) :-

🔹 When electricity is passed through an aqueous solution of NaCl (brine), it decompose to form NaOH.

  • 2Nacl + 2H₂0 → 2NAOH + Cl₂ + H₂
  • At anode : Cl₂ gas 
  • At cathode : H₂ gas 
  • Near cathode : NaOH solution 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

❇️ Bleaching Powder (CaOCl₂) :-

🔹 It is produced by the action of chlorine on dry slaked lime. 

Cl₂ + Ca(OH)₂ → CaOCl₂ + H₂O

🔶 Uses :- 

  • Bleaching cotton and linen in textile industry. 
  • Bleaching wood pulp in paper factories.
  • Oxidizing agent in chemical industries. 
  • Disinfecting drinking water. 

❇️ 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 + H₂0 + CO₂ 

🔶 Uses :- 

  • 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 soft and spongy. 
  • An ingredient in antacid. 
  • Used in soda acids, fire extinguishers.

❇️ Washing Soda (Na,CO,.10H,0) :-

🔹 Recrystallization of sodium carbonate gives washing soda. It is a basic salt. 

Na₂CO₃ + 10H₂0 → Na₂CO₃.10H₂0

🔶 Uses :-

  • In glass, soap and paper industry. 
  • Manufacture of borax.
  • Cleaning agent for domestic purposes.
  • For removing permanent hardness of water.

❇️ Plaster of Paris (Calcium sulphate hemihydrates) (CaSO₄.½H₂0) :-

🔹 On heating gypsum (CaSO₄.H₂0) 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. 

(CaSO₄.½H₂0) + 1½H₂0 → CaSO₄2H₂O 

🔶 Uses :-

  • Doctors use POP for supporting fractured bones.
  • For making toys, material for decoration.  
  • For making surfaces smooth.

❇️ Water of Crystallisation :-

🔹 Certain salts that contain fixed amount of some H₂O molecules loosely attached to their own molecules. They are known hydrated salts and they are of crystalline nature. The molecules of H₂O present are called as ‘water of crystallisation’. Example :-

  • Cuso₄.5H₂0 has 5 water molecules.
  • Na₂CO₃. 10H₂0 has 10 water molecules.
  • Caso₄.2H₂O has 2 water molecules.
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