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Acids, Bases and Salts

Acids

➔ An acid is a compound which when dissolved in water yields hydronium ion (H₃O⁺) as the only positively charged ion.

HCl + H2O ⇌ H₃O⁺ + Cl−

Classification of Acids:

1) Based on strength of Acid

i) Strong Acid:- A strong acid is one that is completely dissociated or ionized in an aqueous solution. It is a chemical species with a high capacity to lose a proton, H⁺.

Eg:- Nitric Acid( HNO3 ), Sulphuric Acid( H2SO4 ), Hydrochloric Acid( HCl )

ii) Weak Acid:- A weak acid is one that is partially dissociated or ionized in an aqueous solution. It is a chemical species with a low capacity to lose a proton, H⁺.

Eg:- Acetic Acid(CH3COOH), Formic Acid( HCOOH), Hydrogen Sulphide( H2S)

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2) Based on Concentration of Acids i) Concentrated Acids:- A Concentrated acid is that in which the concentration of the water mixed in the acid is lesser than the concentration of the acid .

ii) Dilute Acids:- A dilute acid is that in which the concentration of the water mixed in the acid is higher than the concentration of the acid itself.

i) Organic Acids:- Acids that are obtained from plants.

Eg:- Acetic Acid(CH3COOH), Citric Acid(C₆H₈O₇), Oxalic Acid(C2H2O4 )

ii) Inorganic Acids:-Acids that are obtained from Minerals.

Eg:-Nitric Acid( HNO3 ), Sulphuric Acid( H2SO4 ), Hydrochloric Acid( HCl )

3) Based on the source

4) Based on Molecular Composition

i) Oxyacids:- Acid which contains Hydrogen, Oxygen and one more element.

Eg:-Sulfuric acid (H2SO4), Phosphoric acid (H3PO4), and Nitric acid (HNO3) ii) Hydracids:- Acid which contains Hydrogen, and a non metal other than Oxygen.

Eg:- Hydrochloric Acid (HCl), Hydrobromic Acid (HBr), Hydrofluoric Acid (HF)

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5) Based on Basicity i) Monobasic Acid: Acid containing only one replaceable Hydrogen atom.

Eg:- Nitric acid (HNO3) , Acetic Acid(CH3COOH), Hydrochloric Acid(HCl)

ii) Dibasic Acid:- Acid containing two replaceable Hydrogen atom.

Eg:- Sulfuric acid (H2SO4), Oxalic Acid(C2H2O4 ).

iii) Tribasic Acid:- Acid containing three replaceable Hydrogen atom.

Eg:- Phosphoric acid( H3PO4), Phosphorous acid( H3PO3)

iv) Tetrabasic Acid:- Acid containing four replaceable Hydrogen atom.

Eg:- Silicic acid( H4O4Si)

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➔ Acids have a sour taste.➔ Acids are corrosive in nature especially Mineral acids.➔ Acidic solutions are good conductors of electricity.➔ Acids turn blue litmus red.➔ Acids turn Methyl orange pink.➔ Acids turn phenolphthalein colourless.

Uses of Acids:

Properties of Acids:

➔ Hydrochloric acid is used as a lab reagent.➔ Carbonic acid is used as soda water, in aerated drinks as well.➔ Boric acid is used as an eyewash.➔ Acetic acid is used as vinegar.➔ Oxalic acid is used to remove ink stains.➔ Tartaric acid is used as baking powder.➔ Citric acid is used to preserve food items.

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Bases

➔ A base is a compound which when dissolved in water yields hydroxyl ion (OH−) as the only negatively charged ion.

➔ A base is a compound which reacts with an acid to form salt and water.

Classification of Bases:1) Based on strength of Base

i) Strong Base/Alkali:- A strong base/alkali is one that is completely dissociated or ionized in an aqueous solution. It is a chemical species with a high capacity to produce, OH−.

Eg:- Sodium Hydroxide( NaOH ), Potassium Hydroxide( KOH)

ii) Weak Base/Alkali:- A weak base/alkali is one that is partially dissociated or ionized in an aqueous solution. It is a chemical species with a low capacity to produce, OH−.

Eg:- Pure water( H2O ), Ammonia Hydroxide( NH4OH ).

2) Based on Concentration of Acids i) Concentrated Bases:- A Concentrated base is that in which the concentration of the alkali in their aqueous solutions is high.

ii) Dilute Bases:- A Concentrated base is that in which the concentration of the alkali in their aqueous solutions is low.

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5) Based on Acidity i) Monoacidic Alkali: Alkali containing only one replaceable hydroxyl ion.

Eg:- Sodium Hydroxide( NaOH ), Potassium Hydroxide( KOH)

ii) Diacidic Alkali:- Alkali containing two replaceable hydroxyl ion.

Eg:- Magnesium Hydroxide(Mg(OH)2), Calcium Hydroxide(Ca(OH)2).

iii) Triacidic Alkali:- Alkali containing three replaceable hydroxyl ion.

Eg:- Ferric Hydroxide( Fe(OH)3), Aluminium Hydroxide(Al(OH)3)

Properties of Bases:➔ Bases have a soapy touch and a bitter taste.➔ Caustic alkalis (NaOH and KOH) are corrosive in nature.➔ Bases turn red litmus blue.➔ Acids turn Methyl orange yellow.➔ Acids turn phenolphthalein pink.

Uses of Bases:➔ Sodium hydroxide acid is used in manufacture of laundry soaps.➔ Potassium hydroxide is used in alkaline batteries.➔ Calcium hydroxide is used in manufacture of bleaching powder.➔ Aluminium hydroxide is used to remove grease stones from clothes.➔ Magnesium hydroxide is used as an antacid to neutralize acidity caused

in stomach by Hydrochloric acid.

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Salts➔ A substance produced by the reaction of an acid with a base. A salt consists of

the positive ion (cation) of a base and the negative ion (anion) of an acid. The reaction between an acid and a base is called a neutralization reaction.

Acid + Base –> Salt + Water

Eg:- K2SO4, CaSO4, KCl, NaCl

2KOH+H2SO4⟶K2SO4+2H2O

NaOH+H2SO4⟶NaHSO4+H2O

Eg:-[Cu(OH)NO3],[Pb(OH)NO3 ]

Types of Salts

1) Normal Salt:- These are formed by the complete replacement of ionisable hydrogen atom of acid by metallic ion or ammonium ion(basic radical)

2) Acid Salt:- These are formed by the partial replacement of replaceable hydrogen ion of an acid by a metal or ammonium ion ( basic radical).

Eg- KHSO4, NaHSO4,

3) Basic Salts:- These are formed by the partial replacement of hydroxyl radical of a diacidic or triacidic base with an acid radical.

Pb(OH)2+HCl⟶Pb(OH)Cl+H2O

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4) Double Salt:- Type of salt having the composition of a mixture of two simple salts but with a different crystal structure from either.

Eg- Potash alum ( KAl(SO4)2·12H2O ) , Sodium alum (NaAl(SO4)2·12H2O )

5) Complex Salt:- Type of salt having one or more complex ions.

Eg- Potassium argento cyanide (K [Ag(CN)2]) tetra amino cupric sulphate ([Cu(NH3)4]SO4)

General Method of Preparation of SaltsSalts are formed due to chemical reactions between: A base and an acid: NaOH + HCl ⟶ NaCl (neutralization reaction; complete replacement of hydrogen ion by metal)

NaOH+𝐻2𝑆𝑂4⟶𝑁𝑎𝐻𝑆𝑂4+ 𝐻2𝑂 (partial replacement of hydrogen ion by metal)

A metal and an acid: Ca + 𝐻2𝑆𝑂4 ⟶ 𝐶𝑎𝑆𝑂4 + 𝐻2

A metal and a non-metal: Li + 𝐶𝑙2 ⟶ 𝐿𝑖𝐶𝑙2

A base and an acid anhydride: 2NaOH + 𝐶𝑙2𝑂 ⟶ 2𝑁𝑎𝐶𝑙𝑂 + 𝐻2𝑂

An acid and a basic anhydride: 2𝐻𝑁𝑂3 + 𝑁𝑎2𝑂 ⟶ 2𝑁𝑎𝑁𝑂3 + 𝐻2𝑜

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Properties of salts➔ Salts are non-volatile electrovalent compounds.➔ Salts have high melting points .➔ Salts are good conductors of electricity in aqueous

solution.

Water of Crystallization: The number of water molecules present in a salt crystal.

Eg:- (NH4)2Fe(SO4)2·6H2O (6 is the water of crystallization in Mohr’s salt)

Efflorescence: The process of losing water of crystallization by a hydrated salt, when exposed to atmosphere. Eg:- Gypsum (CaSO4.2H2O), Sodium carbonate hydrate (Na2CO3.10H2O)

Deliquescence: Deliquescence is the process by which a substance absorbs moisture from the atmosphere until it dissolves in the absorbed water and forms a solution. Eg:- Magnesium chloride ( MgCl2 ), Calcium chloride ( CaCl2 )

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Fill in the blanks.(a) Chemical formula for bleaching powder is ______.(b) Acids ______ _______ bases to form ________ and water.(c) The term pH was coined by _______ .(d) An acidic solution contains _____ _______ ions .(e)________ ________ is used in softening water.(f) ______ medicine used to treat indigestion(g) Calcium Sulphate hemihydrate is popularly known as _____ ___ _____.(i) ________ are present in aerated drinks

True and False statementa) Vinegar contains acetic acidb) Formic acid is a weak acidc) Acids gives H+ ion in waterd) Baking soda is used for Softening of hard watere) pH of a solution can vary from 0-14.f) Heat is evolved during ionization.g) NaCl is a baseh) Acids turns blue litmus solution to red

Practice Questions

1) Write the chemical name and formula of baking soda.2) Write the name and the chemical formula of the organic acid present in vinegar.3) What is the common name of the compound CaOCl2?4) Name two indicators which are widely used in laboratories.5) What are hydronium ions?6) What is meant by strong acids and weak acids? Classify the following into strong acids and weak acids :-

HCl, HNO3, H2CO3, H2SO3, CH3COOH

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