Acids Bases And Salts Cbse

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Arrhenius acid

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A substance which gives H+ ions in aqueous solution

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Arrhenius base

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A substance which gives OH- ions in aqueous solution

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Neutralization

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Process in which H+ ions of an acid combine with OH- ions of a base to give water while the negative ion of the acid combines with the positive ion of the base to form a salt

It is a double displacement reaction (when both reactants exchange ions

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Properties of Acids

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- Tastes Sour

- Reacts with metals to liberate hydrogen gas

- Turns blue litmus to Red

- Conducts electricity in aqueous solution

- Corrosive in Nature

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Chemical properties of an acid

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Metal + acid = salt + hydrogen gas

Metal oxide + acid = salt + water

Metal carbonate = salt + water + carbon dioxide

Metal hydrogencarbonate = salt + water + carbon dioxide

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Test for CO2 gas

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To test for CO2, we pass the evolved gas through Lime Water(Caustic Lime).

CO2 + Ca(OH)2 => CaCO3 + H2O

The CaCO3 will make a milky white precipitate

However when excess CO2 is passed the milkiness disappears due to formation of Calcium Hydrogencarbonate which is soluble

CaCO3 + H2O + CO2 => CaHCO3

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Properties of Bases

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- Tastes Bitter and Slippery in Nature

- Reacts with non-metals to liberate Hydrogen gas

- Turns red litmus to blue

- Some are soluble in water (alkali)

- Corrosive in Nature as well

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Chemical Properties of a base

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Metal Oxide + Base = Salt + Water

ZnO + 2NaOH = Na2ZnO2 + H2O

Al2O3 + 2NaOH = 2NaAlO2 + H2O

PbO + 2NaOH = Na2PbO2 + H2O

Non metallic Oxide + base = salt + water

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Indicators

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Phenolphthalein- Base - Pink; Acid and Neutral - Colourless

Red Litmus - Base - Blue, Acid and Neutral - Red

Blue Litmus - Base and Neutral - Blue ; Acid - Red

Methyl Orange - Acid- Pinkish Red; Base- Yellow

Olfactory Indicators - Due to smell . Eg - Onions and Vanilla Essence

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Electrolyte

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Compounds that dissolve in water and dissociate into ions.

- Can Conduct electricity

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Strong Electrolyte

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Completely dissociates into ions when in aqueous solution

Eg - Strong Acids - Sulfuric Acid , Hydrochloric Acid

Strong Bases - Caustic Soda, Caustic Potash

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Weak Electrolytes

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Partially dissociates into ions when in aqueous solution

Eg - Weak Acids - Acetic Acid, Oxalic Acid

Weak Bases - Magnesium Hydroxide, Ammonium Hydroxide

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pH and its expression

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Strength of an acid or alkali is measured using a scale of numbers called the pH scale

pH = -log[H+]

Example:

pH = -log[1/10] = log[10] = 1

Acid < pH 7

Base > pH 7

Neutral = pH 7

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Universal Indicator

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- A universal indicator is a pH indicator composed of a solution of several compounds that exhibits several smooth colour changes over a pH value range from 1 to 14 to indicate the acidity or alkalinity of solutions.

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Ionic Product of Water (Kw)

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In any aqueous solution, the product of H+ ion and OH- ion concentration is always constant and equal to 10 raised to -14 at 25 C

(Kw) = [H+] x [OH-] = [1/100,000,000,000,000] (10 raised to minus 14)

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Role of pH in plants

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Before sowing we have to check the pH of the soil to ensure of proper growth. If the soil is too acidic it may negatively effect the plants. Therefore the farmer adds slaked lime to the soil to increase the pH of the soil.

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Role of pH in Bee or Ant stings

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When bitten by a bee or a yellow ant, there is a painful sting due to the presence of formic acid( also called methanoic acid). Therefore we apply a mild base such as milk of magnesia or baking soda to neutralize the acid in the sting

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Role of pH in Stomach

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The stomach's pH is 2.0 due to presence of HCl. This is to activate pepsinogen to become pepsin, provide the medium for pepsin to react and kill any bacteria in the food. However sometimes there could be an increase in the amount of acid during digestion which is called acidity. We neutralize this excess acid by the intake of antacids such as magnesium hydroxide(milk of magnesia).

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Role of pH in Mouth

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pH of mouth is usually about 7. However when we ingest sugary foods or cold drinks, the bacteria in the mouth digest these sugars to give off acids which lower the pH of the mouth and can cause tooth decay. Therefore the toothpaste we use is generally basic in nature to neutralize the acid.

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Factors affecting reaction of acid with metal

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If the metal is below hydrogen in reactive series, it will not react. Example - Copper , Silver, Gold , Platinum.

Also , the higher the metal is in the reactivity series, the faster it reacts with the same acid.

Also the strength of the acid is also important

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Nitric Acid Reaction with copper

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Copper can react with Nitric Acid since Nitric acid is an oxidising agent and the reaction is not the usual acid + metal reaction. The products are oxides of nitrogen instead of hydrogen.There are actually two equations for the reaction of copper with nitric acid. If it is concentrated and in excess then the ratio is 1:4 copper to nitric acid. If it is dilute then the ratio is 3:8.

Cu + 4HNO3 –> Cu(NO3)2 + 2NO2 + 2H2O

3Cu + 8HNO3 –> 3Cu(NO3)2 + 2NO + 4H2O

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Salts and Classification of Salts

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It is a compound formed by replacement of either all or a part of the ionisable hydrogen atoms of an acid by some other cation

There are three types of salts

1)Normal Salts - Salts formed by complete replacement of all ionisable hydrogen atoms pH = 7

2)Acidic Salts - Salts formed by partial replacement of ionisable of an acid by metallic or ammonium ions. pH < 7

3)Basic Salts - Salts formed by partial replacement of hydroxyl groups of a base.

pH > 7

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Water of Crystallization

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Fixed number of water molecules chemically attached to each formula unit of a salt in its crystalline form is called water of crystallization.

The salts containing water of crystallization are called hydrated salts. Eg: CuSO4.5H2O

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NaCl - Common Salt

Preparation and Occurrence

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Preparation - NaOH + HCl => NaCl + H2O

Occurrence:

Sea water- It is one of the main source of common salt. The sea water is allowed to evaporate in shallow tanks under the influence of sun and wind. The salt obtained contains impurities which are removed by suitable methods.

Rock salt- It is also found in the form of solid deposits in several parts of the world. Due to presence of impurities it is often brown in color and is called rock salt. Rock salt is mined just like any other mineral.

Inland lakes- Large quantities of salts are obtained by the natural evaporation of the water of inland lakes

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NaCl - Common Salt

Uses

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1) It is an essential constituent of our diet.

2) It is used as a preservative for a number of food materials eg. In packed meat and fish.

3) It is used for melting of ice on icy roads.

4) It is an important starting material for the production of number of other chemicals such as hydrochloric acid, sodium hydroxide, washing soda, baking soda etc.

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NaOH - Caustic Soda

Preperation

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It is prepared by passing electricity through an aqueous solution of sodium chloride (called brine) in a specially designed cell.

As a result of electrolysis chlorine gas is given off at anode and hydrogen gas at the cathode. Sodium hydroxide solution is formed near cathode. This method is called Chloro-alkali process because the products are chlorine and an alkali.

2NaCl + 2H2O =>2NaOH(aq) + Cl2 (g)+ H2 (g)

At anode:2 Cl- => Cl2 + 2e-

At cathode: 2H+ 2e- => H2

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NaOH - Caustic Soda

Uses

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1)In paper making

2)Manufacturing Salts and Detergents

3)In bauxite purification to extract aluminium

4)In forensic labs for testing carbon monoxide poisoning

5)Used to remove roadkill in roads

6)In the manufacture of dyes.

7)In petroleum refining.

8)For mercerizing cotton, i.e. making cotton no shrinkable.

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Uses of Hydrogen

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1) Making Ammonia which is used in production of fertilizers

2) In production of plastics

3) Used to remove sulphur from fuel

4) Reducing heavy metal oxides to metals

5) Considered future energy source

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Uses of Chlorine Gas

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1) Disinfectant used in drinking water as well as swimming pool water

2) Used in several consumer items like paints, papers

3) Used in textiles and insecticides

4) Used as an oxidising and chloriniation agent

5) Used to make PVC plastic which is used in making cars, insulating wires and flooring tiles

6 ) Was Used to make chloroform but is now restricted due to its adverse affects

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CaCO3.10H2O - Washing Soda

Preperation

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Washing soda is prepared by Solvay's process. In this process carbon dioxide gas is bubbled through saturated ammonical brine solution which results in the formation of sodium hydrogencarbonate.

NaCl+H2O+NH3+CO2=>NH4Cl+NaHCO3

The sodium hydrogen carbonate is filtered off and then ignited to get sodium carbonate.

2NaHCO3 => Na2CO3+ H2O + CO2

Anhydrous Sodium Carbonate (soda ash). The anhydrous sodium carbonate is dissolved in water and then subjected to recrystallisation to obtain crystals of washing soda.

Na2CO3 + 10H2O ------------> Na2CO3.10H2O

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CaCO3.10H2O - Washing Soda

Properties

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It is transparent crystalline solid.It is readily soluble in water and its aqueous solution is alkaline in nature due to hydrolysis.

Na2CO3+2H2O => 2NaOH + H2CO3

When kept open in the air, the crystals of washing soda lose nine molecules of water of crystallization to form a monohydrate which is white powder.

Na2CO3.10 H2O(s) => Na2CO3.H2O(s) + 9H2O The loss of water by a crystalline solid to the atmosphere on exposure to is called efflorescence.

On heating washing soda loses all the molecules of water of crystallization and becomes anhydrous

Na2CO3.10H2O(s)=>Na2CO3 (s)+10H2O(g)↑

Sodium Carbonate (soda ash)It reacts with acid to give out CO2 gas with brisk effervescence.

Na2CO3 + H2SO4 → Na2SO4 + H2O+ CO2 ↑ Washing soda reacts with soluble salts of calcium and magnesium present in hard water to form insoluble salts of calcium and magnesium which can be filtered off, Hence water becomes soft.

Na2CO3+CaCl2 =>CaCO3+2NaCl

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CaCO3.10H2O - Washing Soda

Uses

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It is used in the laundry for cleaning clothes.

It is used in the manufacture of glass, borax, soap and caustic soda.

It is used in paper, paints and textile industries.

It is used for softening of hard water. It removes temporary as well as permanent hardness.

It is used as an important laboratory reagent both in quantitative and qualitative analysis.

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CaOCl2 - Bleaching Powder

Preparation

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It is prepared on industrial scale by passing chlorine gas through dry slaked lime. The plant generally used for the manufacture of bleaching powder is known as 'Hasenclever plant’

Ca(OH)2+Cl2 =>CaOCl2+H2O

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CaOCl2 - Bleaching Powder

Properties

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Bleaching powder is a yellowish white powder which gives strong smell of chlorine.

It is soluble in water leaving behind a small residue of lime. When bleaching powder is exposed to air, it reacts with atmospheric carbon dioxide, giving off chlorine. To avoid decomposition it is packed in air tight containers.

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CaOCl2 - Bleaching Powder

Uses

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For bleaching cotton in textile

For disinfecting drinking water

As an oxidising agent in chemical industry

Making Wool unshrinkable

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NaHCO3 - Baking Soda

Preperation

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Baking soda is obtained as primary product in Solvay's process for the manufacture of sodium carbonate. In this process carbondioxide gas is bubbled through saturated ammonical brine solution which results in the formation of baking soda.

NaCl + H2O + NH3 + CO2 → NH4Cl + NaHCO3

On small scale, it can be prepared in the laboratory by passing carbon dioxide gas through aqueous sodium carbonate solution.

Na2CO3 + H2O + CO2 → NaHCO3

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NaHCO3 - Baking Soda

Properties

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It is white crystalline solid.It is sparingly soluble in water. The solution is alkaline in nature due to salt hydrolysis.

NaHCO3 + H2O → NaOH + H2CO3

Baking soda on heating decomposes to give carbon dioxide.

2NaHCO3 ---Heat ---> Na2CO3+H2O+CO2 ↑

It reacts with acids to liberate carbon dioxide gas with brisk effervescence.

2NaHCO3+H2SO4=> Na2SO4+2H2O+2CO2

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NaHCO3 - Baking Soda

Uses

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It is used as an ingredient in antacids. Being alkaline it neutralizes excess acid in the stomach.

It is used as a component of baking powder (sodium hydrogencarbonate + mild edible acid such as tartaric acid, citric acids etc.)When mixed with water and heated, baking soda decomposes producing carbon dioxide which causes bread or cake to swell and become light. Tartaric acid present in baking powder neutralizes bitter taste of sodium carbonate.

It is used in soda-acid fire extinguishers. Soda acid fire extinguishers contain a solution of hydrogen carbonate and sulphuric acid. These two chemicals are brought in contact by pressing a knob or by inverting the extinguisher. Carbon dioxide is produced which forces a stream of effervescing liquid on the fire. CO2 surrounds the combustible substance and cuts off the supply of air. Thus the fire gets extinguished.

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CaSO4.1/2H2O -

Plaster of Paris

Preperation

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It is prepared by heating gypsum to 373 to 393 K.

CaSO4.2H2O ---393K---> CaSO4. ½ H2O +1½ H2O

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CaSO4.1/2H2O -Plaster of Paris

Properties

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It is a white powder.

When mixed with water and left for half an hour, it sets to hard mass. This is due to rehydration of Plaster of paris to Gypsum

CaSO4. ½ H2O+ 1½ H2O => CaSO4.2H2O

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CaSO4.1/2H2O -Plaster of Paris

Uses

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It is used for setting fractured bones in the right position and in making casts in dentistry.

In making toys, casts for statues, decorative materials, jewelry and cosmetics.

In making the surface smooth, e.g. that of walls, ceiling etc, before paint.

In making chalks for writing on the black board.

In laboratory, for making the apparatus air tight by sealing the gaps at the stopper etc.

In making fire proof materials.