Class – 10

Chemistry

Chapter-2 ACIDS, BASES AND SALTS

Summary & Notes

Introduction

Acids and bases are common solutions that exist everywhere. Almost every liquid that we encounter in our daily lives consists of acidic and basic properties. The word acid is derived from the latin word acidus meaning sour to taste. There are some other substances know as alkalis and bases, whose properties are/is different and opposite to that of acids. The word alkali is derived from the arabic word meaning calcined ashes of plants. These were first isolated from the ashes of plants. Acid can destroy the properties of bases and vice versa, the process being called neutralisation. The table below compares the different properties between them:

ACIDS	BASES
produce a piercing pain in a wound.	give a slippery feel.
taste sour.	taste bitter.
are colorless when placed in phenolphthalein (an indicator).	are pink when placed in phenolphthalein (an indicator).
are red on blue litmus paper (a pH indicator).	are blue on red litmus paper (a pH indicator).
have a pH<7.	have a pH>7.
produce hydrogen gas when reacted with metals.	produce carbon dioxide when reacted with carbonates.
Common examples: Lemons, oranges, vinegar, urine, sulfuric acid, hydrochloric acid	Common Examples: Soap, toothpaste, bleach, cleaning agents, limewater, ammonia water, sodium hydroxide.

In 1884, the Swedish chemist Svante Arrhenius proposed two specific classifications of compounds, termed acids and bases. When dissolved in an aqueous solution, certain ions were released into the solution.

ACIDS

Initially, the substance which were found sour in taste, were called acids. Many fruits and plants are sour in taste due to the presence of an acid. For example, when we cut a lemon and taste its juice, it has a sour taste. Similarly, raw mangoes, oranges, tamarind, etc.. are sour in taste due to the presence of acids in them. Vinegar(ethanoic acid) is an acidic substance and it is used as food preservator. It contains a natural acid which is commonly known as acetic acid.

BASED UPON THEIR SOURCES, ACIDS ARE CLASSIFIED INTO TWO CATEGORIES:

Organic acids
Inorganic acid

I. organic acids: these are the acids which are produced by plants and animals.these are also called natural acids. Ants squirt formic acid at their enemies. When a red ant bites a human-being, it injects a very small amount of formic acid, and due to which there is a swelling on that part of the body.

Organic acids and their sources.

Name of the acid	Source
Tartaric acid	Tamarind and grapes
Citric acid	Lemon juice and orange
Formic acid	Ants, nettle leaf sting
Lactic acid	Milk, curd
Malic acid	Apples
Oxalic acid	Tomatoes, guava
Uric acid	Urine (of animals)

II. Inorganic acid: these are the acids which are prepared from the minerals of the earth. these are found in non-livings things and hence, they are also called man-made acids. The three important mineral acids are hydrochloric acid, sulphuric acid and nitric acid. Concentrated acids are added to distilled water to get dilute minerals acids, which are less harmful.

Name of the acid	Formula
Hydrochloric acid	HCl
Sulphuric acid	H2SO4
Nitric acid	HNO3
Carbonic acid	H2CO3

Sulphuric acid is used in many industries and therefore, it is called ‘king of chemicals’.it is used in batteries of inverters, cars, etc.

BASES

Bases are defined as the substances which have a bitter taste. they are soapy to touch. all the bases turn red litmus paper to blue. Alkalis are those bases which are soluble in water.

Name of alkali	Formula
Sodium hydroxide	NaOH
Potassium hydroxide	KOH
Calcium hydroxide	Ca(OH)2

With the passage of time various theories about acids and bases have been developed, the recent ones being more broad-based. Each of these theories has particular advantages. We shall discuss here two concept of acids and bases:

Arrhenius concept of acids and bases.
Bronsted-lowry’s proton concept of acids and bases.

ARRHENIUS CONCEPT OF ACIDS AND BASES

According to an Arrhenius theory, an acid is a substance that produces hydrogen ios when added to water. Further, when these hydrogen ions combine with water molecules, they produced hydronium ions (H₃O⁺). This process is represented in a chemical equation by adding H₂O to the reactants side.

HCl(aq)→H+(aq)+Cl−(aq)

In this reaction, hydrochloric acid (HCl) dissociates into hydrogen (H⁺) and chlorine (Cl^–) ions when dissolved in water, thereby releasing H⁺ ions into solution. Formation of the hydronium ion equation:

HCl(aq)+ H₃O⁺(l)→ H₃O⁺+(aq)+Cl−(aq)

Strong acids

Strong acids completely dissociate in water, forming H+ and an anion,

e.g. HCl + H2O →

Since it is a strong acid it dissociates completely, you will not have any HCl. In solution we have H3O+ and Cl- ions which concentration is equal HCl concentration.

Strong acids

HCl (hydrochloric acid)
HNO3 (nitric acid)
H2SO4 (sulfuric acid)
HBr (hydrobromic acid)
HI hydroiodic acid
HClO4 (perchloric acid)

Weak acids

A weak acid only partially dissociates in water to give H+ and the anion. Examples of weak acids include hydrofluoric acid, HF, and acetic acid, CH3COOH.

e.g. HF + H2O ↔ + F-

CH3COOH (acetic acid)
HCOOH (formic acid)
HF (hydrofluoric acid)
HCN (hydrocyanic acid)
HNO2 (nitrous acid)
HSO4- (hydrogen sulfate ion)

ARRHENIUS BASES

According to the An Arrhenius theory, base is a compound that increases the concentration of OH^– ions when added to water. the following equation:

NaOH(aq)→Na+(aq)+OH−(aq)

In this reaction, sodium hydroxide (NaOH) disassociates into sodium (Na⁺) and hydroxide (OH^–) ions when dissolved in water, thereby releasing OH^–ions into solution.there are very few common strong bases and Weak bases are.

Strong base:Strong bases dissociate 100%(completely) into the cation and OH- (hydroxide ion).

For example: NaOH(aq)→Na+(aq)+OH−(aq)

LiOH

NaOH sodium hydroxide
KOH potassium hydroxide
Ba(OH) 2 barium hydroxide

Weak bsae

Weak bases do not furnish OH- ions by dissociation. Instead, they react with water to generate OH- ions

NH3 ammonia
CH3NH2 methylamine
C5H5N pyridine
NH4OH ammonium hydroxide

LIMITATIONS TO THE ARRHENIUS THEORY

1. ARRHENIUS THEORY does not explain the weak base ammonia (NH₃), which in the presence of water, releases hydroxide ions into solution, but does not contain OH- itself.

Hydrochloric acid is neutralised by both sodium hydroxide solution and ammonia solution. In both cases, you get a colourless solution which you can crystallise to get a white salt – either sodium chloride or ammonium chloride. These are clearly very similar reactions. The full equations are:

NaOH(aq)+HCl(aq)→NaCl(aq)+H2O(l)

NH3(aq)+HCl(aq)→NH4Cl(aq)

In the sodium hydroxide case, hydrogen ions from the acid are reacting with hydroxide ions from the sodium hydroxide – in line with the Arrhenius theory. However, in the ammonia case, there are no hydroxide ions!

2.arrehnius theory could not explain the acidic nature of substances which doesnot contain hydrogen.For example non metal oxide generally contain acidic in nature,but they donot contain hydrogen. Such as CO2,SO3..etc

3.arrehenius theory failed to explain the neutralisation reactions which donot involve in formation of water.

For example: CaO + CO2 → CaCO3

Properties of acids

A characteristic sour taste.
ability to change the color of litmus paper from blue to red.
react with certain metals to produce gaseous H₂ .
react with bases to form a salt and water.
Acids release a hydrogen ion into water (aqueous) solution.
Acids neutralize bases in a neutralization reaction.
Acids corrode active metal

Properties of bases

Bases are usually oxides and hydroxides of metals. Bases that dissolve in water are called alkalis.
Bases are bitter to taste and soapy to touch.
Bases turn red litmus paper blue.
Bases are characterised by the presence of hydroxyl (-OH) group.
Bases react with acids to form salt (a neutral substance) and water.
Bases are corrosive to skin; they should not be touched by hand

CHEMICAL PROPERTIES OF BASES AND ACID

1) When a strong acid and a strong base solution are mixed, a neutralization reaction occurs, and the products do not have characteristics of either acids or bases. Instead, a neutral salt and water are formed. Look at the reaction below:

HCl_(aq) + NaOH_(aq) → H₂O_(l) + NaCl_(aq)

The anion from the acid (Cl^–) reacts with the cation from the base (Na⁺) to give a salt, and a salt is defined as any compound formed whose anion came from an acid and whose cation came from a base.

2) When a strong acid and a weak base are mixed, the resulting salt will be acidic.

strong acid + weak base,

e.g., HCl + NH₃ → NH₄Cl

The reaction between a strong acid and a weak base also produces a salt, but water is not usually formed because weak bases tend not to be hydroxides. In this case, the water solvent will react with the cation of the salt to reform the weak base.

3) if a strong base and a weak acid are mixed, the resulting salt will be basic.

weak acid + strong base,

e.g., HClO + NaOH → NaClO + H₂O

When a weak acid reacts with a strong base the resulting solution will be basic. The salt will be hydrolyzed to form the acid, together with the formation of the hydroxide ion from the hydrolyzed water molecules.

4) weak acid + weak base, e.g., HClO + NH₃ ↔ NH₄ClO

The pH of the solution formed from the reaction of a weak acid with a weak base depends on the relative strengths of the reactants.

CHEMICAL REACTION

1.How do Acids React with Metals ?

All metals above hydrogen in the metal reactivity series generally react with dilute acids to form their respective salt and liberate hydrogen.

Metal + Acid Salt + Hydrogen

2Na + H₂Co₃ —→ Na₂Co₃ + H₂

When a base combine with metal it forms metal salt / base and release hydrogen gas

2.How do metal carbonate and hydrogen carbonate react with acids to give a corresponding salt, carbon dioxide and water?

All metal carbonates and hydrogen carbonate react with acids to give a corresponding salt, carbon dioxide and water.

Metal carbonate / metal hydrogen carbonate + acid –-→ salt +CO₂ + H₂O

Na₂CO₃ + 2HCl –-→ 2Nacl + H₂O + CO₂

NaHCo₂ + Hcl –-→ H₂O + H₂O + CO₂

Limestone, chalk and marble are different form of calcium carbonate

3. Reaction of Metallic Oxides with Acids.

Metals oxides will react with dilute acids to give a salt and water.

Metal oxide + acid –-→ salt + water

CuO + H₂SO₄ –→ CuSO₄ + H₂O

Acids react with metallic oxides to give salt and water similar to the reaction acid and base So, metallic oxides are called basic oxide.

4. Reaction of Base with Metals:

When alkali (base) reacts with metal, it produces salt and hydrogen gas.

Alkali + Metal —→ Salt + Hydrogen

Example: Sodium hydroxide gives hydrogen gas and sodium zincate when reacts with zinc metal.

2NaOH + Zn —-→ Na₂ZnO₂ + H₂

Sodium aluminate and hydrogen gas are formed when sodium hydroxide reacts with aluminium metal.

2NaOH + 2Al + 2H₂O ⇨ 2NaAlO₂ + 2H₂

5. Reaction of base with acid( Neutralisation):

A base neutralizes an acid when they react with each other and respective salt and water are formed.

Acid + Base ⇨ Salt + Water

Since in the reaction between acid and base both neutralize each other, hence it is also known as neutralization reaction.

Example: Sodium chloride and water are formed when hydrochloric acid reacts with sodium hydroxide (a strong base).

HCl + NaOH ⇨ NaCl + H₂O

)

Calcium hydroxide hydrochloric acid calcium chloride water

6.reaction with non-metal oxides: non-metal oxides react with a base to produce salt and water.

Non –metal oxide + base ——–→ salt + water

For example,

The reaction clearly indicate that non-metal oxides are acidic in nature.

Uses of Acids:

1. Vinegar, used in the kitchen, is a liquid containing 3-6% acetic acid. It is used in pickles and in many food preparations.

2. Lemon and orange juice contains citric acid. Citric acid is used in the preparation of effervescent salts and as a food preservative.

3. Acids have been put to many uses in industry. Nitric acid and sulphuric acid are used in the manufacture of fertilizers, dyes, paints, drugs and explosives.

4. Sulphuric acid is used in batteries, which are used in cars, etc. Tannic acid is used in the manufacture of ink and leather.

5. Hydrochloric acid is used to make aqua regia, which is used to dissolve noble metals such as gold and platinum.

6. Sulphuric acid is used in manufacturing fertilizers such as super phosphate, ammonium sulpahte etc.

Uses of Bases:

1. Sodium hydroxide (caustic soda) is used in the manufacture of soap. It is used in petroleum-refining in making medicines, paper, pulp, etc. It is used in making rayon.

2. Calcium hydroxide is also known as slaked lime. It is used to neutralize acid in water supplies; in the manufacture of bleaching powder; as a dressing material for acid burns; as an antidote for food poisoning; in the preparation of fungicides and in the mixture of whitewash. It is mixed with sand and water to make mortar which is used in the construction of buildings. It is also used by farmers on the fields to neutralize the harmful effects of acid rain.

3. Ammonium hydroxide is used to remove ink spots from clothes and to remove grease from window-panes. It is used in the cosmetic industry.

4. Alkalis are used in alkaline batteries. Generally, potassium hydroxide is used in such batteries.

ACIDITY OR ALKALINITY OF A SOLUTION IN TERMS OF PH

Water is slightly ionized into ions. In pure water, concentrations of hydrogen ions(H+) and hydroxide ions( ) are equal. Due to this fact, pure water is neither acidic nor basic, it is thus neutral in nature. At 25 C, it is found that the concentration is equal to

Concentration of

For pure water, the product of H⁺ions concentration and OH^– ion concentration is always constant and equal to .this is called ionic product of water and is represented by the symbol

Since acids increase the amount of H⁺ ions present and bases increase the amount of OH^–ions, under the pH scale, the strength of acidity and basicity can be measured by its concentration of H⁺ ions. This scale is shown by the following formula:

pH = -log[H⁺]

with [H⁺] being the concentration of H⁺ ions.

pH of a solution is define as the negative logarithm of hydrogen ion concentration.

In case of neutral solution

pH = -log[H⁺]

= -log( ) = -(-7) log10

= 7

The pH scale is often measured on a 1 to 14 range, but this is incorrect. Something with a pH less than 7 indicates acidic properties and greater than 7 indicates basic properties. A pH at exactly 7 is neutral. The higher the [H⁺],the lower the pH.

Figure . The pH scale shows that substances with a pH greater than 7 are basic and a pH less than 7 are acidic.

‘universal indicator’ is a mixture of different indicators or dyes which show different colour at different pH values. it is used to indicate the acidity or alkalinity of solution. The colour is used to indicate pH directly.

Indicator	Acidic medium	Basic medium
Methyl orange	Orange-red	Yellow
Phenolphthalein	Colourless	Pink
Methyl red	Red	Yellow
Phenol red	Yellow	Red

Action of Litmus solution in an acid and a base:

The Litmus solution is another indicator used to identify the acidic and basic nature of a substance. It is a solution of different dyes extracted from lichen plants.
Acids have a property to change the colour of blue litmus to red and bases change the colour of red litmus to blue.

Standard pH colour chart

pH	Colour of universal indicator	pH	Colour of universal indicator
0	Dark red	8	Greenish blue
1	Red	9	Blue
2	Red	10	Navy blue
3	Orange red	11	Purple
4	Orange	12	Dark purple
5	Orange yellow	13	Violet
6	Greenish yellow	14	Dark violet
7	Green

pH values of some substances:

Solution	pH	Solution	pH
Battery acid	0.5	Human saliva	6.5-7.5
Hydrochloric acid	1	Human blood	7.4
Lemon juice	2-2.5	Tooth paste	8.0
Soft drinks	6.0	Washing soda solution	10.5
Milk	6.5	House hold ammonia	11.6
Pure water	7.0	Sodium hydroxide	14

UNDERSTANDING THE IMPORTANCE OF PH IN EVERYDAY LIFE

1. pH in our digestive system:

Our stomach produces hydrochloric acid. This dilute hydrochloric acid helps in digesting our food without harming the stomach. Sometime, excess of acid is produced in the stomach for various reasons such as overeating.

The excess acid in the stomach causes indigestion which produces pain and irritation. In order to cure indigestion and get rid of pain, we can take bases called antacids. Being basic in nature, antacids react with excess acid in the stomach and neutralize it. The two common antacids used for curing indigestion due to acidity are Magnesium hydroxide (Milk of Magnesia) and Sodium hydrogen carbonate.

2. pH change as the cause of tooth decay:

When we eat food containing sugar, then the bacteria present in our mouth break down the sugar to form acids such as lactic acid.

Thus, acid is formed in the mouth after a sugary food has been eaten. This acid lowers the pH in the mouth making it acidic. Tooth decay starts when the pH of acid formed in the mouth falls below 5.5. This is because then the acid becomes strong enough to attack the enamel of our teeth and corrode it. This sets in tooth decay. The best way to prevent tooth decay is to clean the mouth thoroughly after eating food by rinsing it with lots of clean water. Many tooth pastes contain bases to neutralise the. Mouth acid. The pH of tooth paste is about 8.0. Therefore, using the tooth paste, which is generally basic, for cleaning the tooth can neutralise the excess acid in mouth and prevent tooth decay.

3. Soil pH and plant growth:

Most of the plants grow best when the pH of the soil is close to 7. If the soil is too acidic or too basic the plants grow badly or do not grow at all. The soil may be acidic or basic naturally. The soil pH is also affected by the use of chemical fertilizers in the fields.

Most often the soil in the Fields is too acidic. If the soil is too acidic, (having low pH), then it is treated with materials like quick lime (.calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate). If the soil is too alkaline then its basicity is reduced by adding decaying organic matter which is acidic.

4. pH range and survival of animals:

Our body works well within a narrow pH range of 7.0 to 7.8. If due to some reason, this pH range gets disturbed in the body of a person, then many ailments can occur. The aquatic animals (like fish) can survive in river water within a narrow range of pH.

When the pH of rain water is about 5.6, it is called acid rain. Too much acid rain can lower the pH of river water to such an extent (and make it so acidic) that the survival of aquatic animals becomes difficult. The high acidity of river water can even kill the aquatic animals (like fish). Acids are also present on other planets. For example, the atmosphere of planet Venus is made up of thick white and yellowish clouds of sulphuric acid. Hence, life cannot exist on the planet Venus

SALTS

We’ve all heard of salt, right? Those white crystals we put on our fries are the kind of salt we are most familiar with, but what do we really mean in chemistry when we refer to something as a salt? In chemistry, a salt is an ionic compound which is made up of two oppositely charged ions called a cation (positive) and an anion (negative).

Salts can be easily identified, since they usually consist of positive ions from a metal with negative ions from a non metal. The salt we put on our fries is actually sodium chloride and is made up of metal Na1+ and non metal Cl1- ions. Often you will see this written as Na+ and Cl- (the 1 is dropped) or simply NaCl.

The most familiar salt is sodium chloride, the principal component of common table salt. Sodium chloride, NaCl, and water, H₂O, are formed by neutralization of sodium hydroxide, NaOH, a base, with hydrogen chloride, HCl, an acid: HCl+NaOH→NaCl+H2O.they are made up of ions rather than molecules.

A salt that has neither hydrogen (H) nor hydroxyl (OH) in its formula, e.g., sodium chloride (NaCl), is called a normal salt.salt are classified on two basis, i.e.

On the basis of acids
On the basis of bases, from which they obtained.

I. on the basis of acids

Chloride salts: these salts are obtained by the reaction of hydrochloric acid with any base.

Some important chloride salts are calcium chloride, magnesium chloride, ammonium chloride…etc

b) Sulphate salts: these salts are obtained by the reaction of sulphuric acid with a base.

e.g potassium sulphate, calcium sulphate, sodium sulphate …etc

II. on the basis of bases

Salt obtained from same base are grouped in the same family. For example, when sodium hydroxide (NaOH) is used to react with different acids, then the salts obtained are called ‘sodium salts’. Similarly, salt obtained from KOH are called ‘potassium salts’. A salt that has hydroxyl in its formula, e.g., basic lead nitrate (Pb[OH]NO3), is called a basic salt.

Since a salt may react with a solvent to yield different ions than were present in the salt , a solution of a normal salt may be acidic or basic; e.g., trisodium phosphate, Na3PO4, dissolves in and reacts with water to form a basic solution.

PREPARATION OF SODIUM HYDROXIDE

Sodium hydroxide, also known as caustic soda or lye, is an inorganic compound with the chemical formula NaOH. It is a white solid, and is a highly caustic metallic base and alkali salt. It is available in pellets, flakes, granules, and as prepared solutions at a number of different concentrations.

Sodium hydroxide is industrially produced as a 50 per cent solution by variations of the electrolytic chloralkali process. Chlorine gas is also produced in this process. Solid sodium hydroxide is obtained from this solution by the evaporation of water.

Castner – Kellener Process

Principle – In castner-kellner method NaOH is prepared by the electrolysis of aqueous solution of NaCl (Brine).

Castner-kellner cell – It is a rectangular tank of steel. Inside of tank is lined with ‘ebonite.’ Anode is made of titanium. Flowing layer of mercury (Hg) at the bottom of tank serves as cathode.

Ionization of NaCl – 2NaCl e^– 2Na⁺ + 2Cl^–

When electric current is passed through brine, +ve and -ve ions migrate towards their respective electrodes. Na⁺ ions are discharged at mercury cathode. The sodium deposited at mercury forms Sodium Amalgam. Chlorine produced at the anode is removed from the top of the cell.

Reaction at cathode

2Na+ +2 e^– → 2Na

(Na forms amalgam)

Na + Hg → Na/Hg

Na+ ions are discharged in preference to H+ ions due to high over voltage.

Reaction at anode

2Cl^– → Cl2 + 2e^–

Formation of NaOH

Amalgam moves to another chamber called ‘denuder,’ where it is treated with water to produce NaOH which is in liquid state. Solid NaOH is obtained by the evaporation of this solution.

2Na/Hg + 2H₂O → 2NaOH + H₂ + 2Hg

NaOH obtained is highly pure and the process is very effeicient.

Physical properties

Pure sodium hydroxide is a whitish solid, sold in pellets, flakes, and granular form, as well as in solution. It is highly soluble in water, with a lower solubility in ethanol and methanol, but is insoluble in ether and other non-polar solvents. Similar to the hydration of sulfuric acid, dissolution of solid sodium hydroxide in water is a highly exothermic reaction in which a large amount of heat is liberated, posing a threat to safety through the possibility of splashing. The resulting solution is usually colourless and odorless with slippery feeling upon contact in common with other alkalis.

CHEMICAL PROPERTIES

Reaction with acids

Sodium hydroxide reacts with protic acids to produce water and the corresponding salts. For example, when sodium hydroxide reacts with hydrochloric acid, sodium chloride is formed:

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

In general, such neutralization reactions are represented by one simple net ionic equation:

OH⁻(aq) + H⁺(aq) → H₂O(l)

This type of reaction with a strong acid releases heat, and hence is exothermic. Such acid-base reactions can also be used for titrations. However, sodium hydroxide is not used as a primary standard because it is hygroscopic and absorbs carbon dioxide from air.

Reaction with acidic oxides

Sodium hydroxide also reacts with acidic oxides, such as sulfur dioxide. Such reactions are often used to “scrub” harmful acidic gases (like SO₂ and H₂S) produced in the burning of coal and thus prevent their release into the atmosphere. For example,

2 NaOH + CO₂ → Na₂CO₃ + H₂O

Reaction with amphoteric metals and oxides

Amphoteric oxides are metallic oxides, which show both basic as well as acidic properties. When they react with an acid, they produce salt and water, showing basic properties. While reacting with alkalies they form salt and water showing acidic properties, e.g.,

ZnO+2HCl → ZnCl2(zincchloride) + H2O(basicnature)

ZnO+2NaOH → Na2ZnO2(sodiumzincate) +H2O (acidicnature)

Al2O3+3H2SO4 → Al2(SO4)3+3H2O(basicnature)

Al2O3+2NaOH→2NaAlO2+H2O(acidicnature)(16)

Amphoteric oxides have both acidic and basic properties. A common example of an amphoteric oxide is aluminum oxide. In general, amphoteric oxides form with metalloids. (see chart below for more detail). Example with acidic properties:

Al2O3+H2O→2Al(OH)+2H+

Example with basic properties:

Al2O3+H2O→2Al3+ + 3OH−

2 Al + 2 NaOH + 6 H₂O → 2 Na[Al(OH)₄] + 3 H₂

Used in processes to make products including plastics, soaps rayon and textiles
Revitalizing acids in petroleum refining

Removal paint
Etching aluminum
Dehorning of cattle
During two steps of the paper making process
Used in relaxers to help straighten hair however this is becoming less popular because of the possibility of chemical burns.

WASHING SODA

Chemical name – sodium carbonate

Chemical formula – Na₂CO₃. 10H₂O

Common name – washing soda

Raw material
Sodium Chloride (Nacl)
lime stone (Caco₃)
Ammonia (NH₃)
Water (H₂O)

Principle:The process is based on the principle of formation and decomposition of ammonia bicarbonate leading to sodium bicarbonate salt.

Process:The process is very simple and consist of following steps.

1. Saturation of Brine With Ammonia.

Brine solution is introduced from the top to the tower where ammonia is injected from the bottom, this saturate the brine solution with ammonia.

2. Carbonation.

The saturated brine solution by ammonia is taken to the carbonating tower where it is spread down and carbon dioxide gas is passed trough it. The reaction take place leading to the tower leading to the formation of sodium bicarbonate.

NH₃ + Co₂ + H₂o —> NH₄HCo₃.

NH₄Hco₃ + NAcl —> NaHco₃ + NH₄cl.

3. Filtration::The solid sodium bicarbonate is filtered, washed with cold water and then dried.

4. Calcination:

The dried crystals of sodium bicarbonate are roasted in cylindrical vessels where sodium bicarbonate is converted into sodium carbonate, the carbon-dioxide produced is returned to the process.

2NaHCO3 (s) -heat–> Na₂Co₃ (s) + Co₂ (g) + H₂o(g)

Anhydrous sodium carbonate (Na₂Co₃) is dissolved in water and washing soda is obtained after recrystallisation.

Soda ash water washing soda

Uses of washing soda

Washing soda have great role in daily life and is considered as most commonly used chemical. Some of these uses include:
1. It is used for cleaning and laundry purposes.
2. Main compound in softening hard water.
3. Used in manufacture of products like soap, glass, caustic soda and borax.
4. Used in various industries like textile, paper and paint.
5. This compound is also used in analysis of organic compounds and elements

BLEACHING POWDER

Bleaching powder is obtained by the action of chlorine on dry slaked lime (Hasenclever method).

Ca(OH)₂ + Cl₂ —313K———> CaOCl + H₂O

An aqueous solution of bleaching powder gives tests for Cl^– and ClO^– ions. On long standing, it undergoes auto-oxidation to form calcium chlorate. However, when heated, in presence of COCl₂, it gives O₂

6CaOCl₂ ———> 5CaCl₂ + Ca (Cl₃)₂

CaCl₂

2CaOCl₂ ———> 2CaOCl₂ + O₂

It is used for bleaching cotton, wood pulp etc., as a disinfectant, as a germicide for sterilization of drinking water, in the manufacture of chloroform and for making wood unshrinkable.

Laboratory Preparation Of Bleaching Powder:

In the laboratory bleaching powder can be prepared by shaking freshly prepared slaked lime Ca(oH)₂. In a jar of chlorine.

Ca(oH)₂ + Cl₂—> Ca(ocl)Cl + H2o

Properties

It is a white ,amorphous powder that smell strongly of chlorine.
1. When exposed to air ,it deteriorate giving off chlorine.

3) Reaction with Water:when bleaching powder react with water slaked lime formed and release chlorine gas
Ca(OC)Cl + H2O —–→ Ca(OH)2 + Cl2

4) It reacts with acids to set free chlorine ,water and calcium chloride.

CaOCl2 + 2HCl —-> CaCl2 + H2O + Cl2

5) It reacts with atmospheric CO2 and moisture to give following reaction.
2CaOCl2 + CO2 + H2O —-> CaCO3 + CaCl2 + 2HOCl .

Uses of Bleaching Powder

1. It is used for sterilization of drinking water.
2. It is used for bleaching of cotton, linen and paper pulp.
3. It is used for the preparation of Cl2 gas and chloroform (CHCl3)

BAKING SODA

Chemical formula – NaHCO₃

Chemical name – sodium hydrogen carbonate

Common name – baking soda

Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder.

NaHCO₃ is mainly prepared by the Solvay process, which is the reaction of sodium chloride, ammonia, and carbon dioxide in water. Calcium carbonate is used as the source of CO₂ and the resultant calcium oxide is used to recover the ammonia from the ammonium chloride. The product shows a low purity (75%).

NaHCO₃ may be obtained by the reaction of carbon dioxide with an aqueous solution of sodium hydroxide. The initial reaction produces sodium carbonate:

CO₂ + 2 NaOH → Na₂CO₃ + H₂O

Further addition of carbon dioxide produces sodium bicarbonate, which at sufficiently high concentration will precipitate out of solution:

Na₂CO₃ + CO₂ + H₂O → 2 NaHCO₃

Uses

It uses in the manufacture of baking powder.
1. It is largely used in the medicine as soda bicarb
1. It is important for textile , tanning , paper , ceramic industries.
1. It also used in fire extinguishers.

PLASTER OF PARIS

The molecular formula of Plaster of Paris is CaSO4. 1/2 H2O
Preparation of Plaster of Paris
When Gypsum (CaSO4.2H2O) is heated to about 100ºC, it loses some water of crystallization and is converted to Plaster of Paris.

It is prepared by precipitating a solution of calcium chloride or nitrate with dilute sulphuric acid.

The effect of heat on gypsum or the dihydrate presents a review of interesting changes. On heating the monoclinic gypsum is first converted into orthorhombic form without loss of water. When the temperature reaches 120°C, the hemihydrate or plaster of paris is the product. The latter losses water, becomes anhydrous above 200°C and finally above 400°C, it decomposes into calcium oxide.

2CaSO₄ ——→ 2CaO + 2SO₂↑ + O₂↑

The following conditions are necessary

(i) The temperature should not be allowed to rise above 393 K because above this temperature the whole of water of crystallization is lost. The resulting anhydrous CaSO₄ is called dead burnt plaster because it does not have the properties of setting with water.

(ii) The gypsum should not be allowed to come in contact with carbon containing fuel otherwise some of it will be reduced to calcium sulphite.

Properties

It is a white powder. On mixing with 1/3^rd its weight of water, it forms a plastic mass which sets into a hard mass of interlocking crystals of gypsum within 5 to 15 minutes. It is due to this reason that it is called plaster. The addition of common salt accelerates the rate of setting, while a little borax or alum reduces it. The setting of plaster of paris is believed to be due to rehydration and its reconversion into gypsum.

2CaSO₄. 1/2 H₂O + 3H₂O ——→ 2CaSO₄. 2H₂O

Plaster of Paris gypsum

Uses

(i) Plaster of pairs is used for producing moulds for pottery and ceramics & casts of statues & busts.

(ii) It is used in surgical bandages used for plastering broken or fractured bones.

(iii) It is also used in dentistry.

Activity corner

Activity 2.1

asks us to test various acids and bases with various reagents one by one and see the result.

Explanation: Various reagents mentioned here are PH indicators. We find its use them in chemistry practicals.

Blue Litmus Paper: It is a reagent to test for basic PH. In acidic PH it turns red.

Red litmus paper: It turns blue in basic PH.

Phenolphthalein : (pronunciation : L silent)it is a colourless reagent.it turns in basic PH.

Methyl orange : it is a narrow range PH indicaotor. T ph below 3.1 it is red and pH above 4.4 it is yellow.

OBSERVATION:

Stronger acids like Hydrochloric acid, Sulphuric acid, Nitric acid have very acidic PH. So, it turns blue litmus into red and gives a red solution with methyl orange. Similarly, Stronger bases like sodium hydroxide, calcium hydroxide, potassium hydroxide, magnesium hydroxide, and ammonium hydroxide turn the red litmus into the blue. With phenolphthalein, they give a pink solution and with methyl orange they give a yellow solution.

For weak acid and bases:

The PH of weak acids and bases depend on their concentration.

For example

Acetic acid: The 1M solution has a PH of 2.88. So It turns Red litmus blue. Phenolphthalein indicates only basic PH so there is no change in the colour with phenolphthalein. It turns methyl orange into the red.

INFERENCE/CONCLUSION:

Different PH indicators give different colour with the acids and bases. An acid turns the red litmus paper blue while a base reveres this. Bases give red colour with phenolphthalein while with methyl orange it gives a yellow solution. Similarly, acids give red colour with methyl orange.

Application: we use indicators in an cid-base rection to finding the endpoint. After completion of a reaction, any addition of a reactant changes the ph of the solution. If suitable ph indicator is present in the solution, it change the colour which marks the endpoint.

Some extra point:

Salt of a strong acid and strong bases like sodium chloride have PH near 7.Salt of Stong acid and a weak base, e.g. copper Sulphate (CuSO4) have acidic PH.Similarly Salt of a Strong base and weak acid, e.g. Calcium carbonate (CaC03) have basic PH.

Activity 2.2

asks us to check the change in odour and colour of cloth soaked with onion and vanilla with acids and bases.

Observation: Bases deodorise onion and vanilla but do not change the colour.

Explanation: The odour and colour of Onion:

Onion contains sulphurous allium. It gives the peculiar onion odour. It is acidic n reacts with bss like sodium hydroxide to gives the odourless compound. So when add bases to onion soaked clot, its smell disappears.

Allium does not react with acid, so when we add acid to onion soked cloth smell remains in the clooth.

colour of onion: there is no relation to the reaction and colour. So the colour remains the same.

The odour and colour of Vanilla:

Vanilla contains an aldehyde which gives it a pleasant odour. The aldehyde is also weak acids. They react with bases, and the smell disappears.

Similar to onion vanilla colour also has no relation with bases and acids. As a result, we do not see any changes in the colour of vanilla with acids or bases.

APPLICATION:

You must have seen onion dipped in a red colour solution in home or restaurant. This red colour solution is potassium permanganate. It is a slightly basic salt. It deodorises the onion smell and also helps in preserving onion for a long duration.

Activity 2.3

asks us to react zinc granules with various acids and observe the flammability of gas formed.

Observation:

We see bubbles coming out vigorously with strong acids. This gas burn when we bring the candle to it. Zinc also react with weak acids like acetic acid, but here gas formation is slow.

Explanation:

Zinc reacts with acids and forms its salt and hydrogen gas. Hydrogen gas liberates as the bubble. When we bring the flame to this gas, it burns as hydrogen is highly flammable.

For example

Zn + H2SO4 ———> ZnSO4 + H2

Weak acid does not dissociate quickly in water. So its reaction with zinc is slower as compared to strong acids like Hydrochloric acid and sulphuric acid.

Activity 2.4

asks us to treat zinc granule with bases like sodium hydroxide.

Observation: Bubbles come out from zinc granule which burns with a flame.

Explanation: Just like a metal reacts with acid (see Activity 2.3), metal also react to bases and produce hydrogen gas.

Here, zinc reacts with sodium hydroxide and form oxide of zinc with the evolution of hydrogen. The reaction is vigorous. So we use dilute bases to moderate the reaction.

Zn(s) + 2NaOH(aq) ———-> Na₂ZnO₂(s) + H₂(g)

Activity 2.5 asks us to react metal carbonates and metal hydrogen carbonate with acids and see if any gas evolves; check also if gas gives a precipitate with quick lime.

Observation:

When we add acid to carbonates and hydrogen carbonates of metal, bubbles start appearing from the carbonates. When we pass this air to a quick lime solution, it turns the lime water milky.

Explanation:

Carbonates and hydrogen carbonates of metal contain carbonate group CO3 in it. The metal forms its salt with acid and produces carbon dioxide gas and water.

Na₂CO₃(s) + 2HCl(aq) ——–> 2NaCl(aq) + H₂O(l) + CO₂(g)

NaHCO₃(s) + 2HCl(aq) ——–> NaCl(aq) + H₂O(l) + CO₂(g)

Carbon dioxide reacts with lime turns the lime (Ca(OH)₂) and forms calcium carbonate. Calcium carbonate is insoluble in water. Its power form makes water milky. Activity 1.4

Ca(OH)₂(aq) + CO₂(g) ——–> CaCO₃(s) + H₂O(l)

Inference/conclusion:

This experiment shows that all metal carbonates and metal hydrogencarbonates react with acids and form carbon dioxide

Activities 2.6

This activity asks us to add a few drops of phenolphthalein into dilute sodium hydroxide and see what happens when we add dilute acid.

Observation: A time comes after adding acid that pink solution of phenolphthalein disappears. Now again if we start adding sodium hydroxide it becomes pink.

Explanation:Phenolphthalein is a colourless reagent. It turns the solution into pink at basic PH. So, It is used in an acid-base titration to see the endpoint. Like here adding acid neutralises the base present in the test tube. Now at the endpoint of the reaction, the addition of an extra drop of acid makes the solution acidic. As a result, the pink colour disappears. Situation reverse when we add a base to this acidic solution. As a result, the solution gets own previous pink colour.

Inference/conclusion: A change in colour of PH indicator can indicate the completion of a reaction

Activity 2.7

asks us to add dilute hydrochloric acid to copper oxide and check the solution of the colour.

OBSERVATION:The colour of the solution turn green.

EXPLANATION: Copper oxide is black; it reacts with hydrochloric acid to form copper chloride. Copper chloride is brown but it absorbs water and turns the solution into a green colour.

CuO(s) + HCl(aq) ————> CuCl₂(aq) + H₂O(l)

APPLICATION: Copper is an ornamental metal. Many small idols of the Gods are made of copper. This turn into black and green by reacting with atmospheric air. People use the acidic nature of lime to wash this colour

activity 2.8

asks us to pass electricity through the various solution and see if bulb glow.

OBSERVATION:The bulb glows with Hydrochloric acid and sulphuric acid but does not glow with alcohol or glucose solution.

EXPLANATION: Acid ionises in water solution. As a result, ions are freely available in the water to conduct electricity. As a result, bulb glow. Alcohol and glucose are organic compounds. They do not ionise in water. As a result, such a solution does not conduct electricity.

INFERENCE/CONCLUSION: Acids, bases and salts increase the electrical conductivity of the water

Activity 2.9

asks us to react solid sodium chloride with concentrated sulphuric acid and check if the gas evolved turn the blue litmus paper into the red or not.

OBSERVATION:Gas fumes produce but do not turn the blue litmus paper into the red.

EXPLANATION: Solid sodium chloride reacts with concentrated sulphuric acid and forms dry hydrochloric acid gas. Here HCl is produced in gaseous form as there is no water.

NaCl(S) + H₂SO₄(Conc.) ———> Na₂SO₄(s)+ HCl(g)

A litmus paper works on H+ or OH- ion. Since there is no water in HCl gas, HCl does not dissociate into its ion and does not turn the blue litmus red.

HCl (aq) ——-> H⁺ + Cl^–

Inference/Conclusion: Concentrated acids and bases need an aueous medium to turn litmus paper.

Activity 2.10

asks us to add a few drops of concentrated sulphuric acid slowly into a beaker containing water and see if heat produces.

OBSERVATION:When we touch the bottom of the beaker, it feels hot

EXPLANATION: Diluting an acid or base into water is an exothermic reaction. Here hydrogen ion interacts with a water molecule and forms hydronium ion. In this process, heat evolves which make the beaker hot.

H₂SO₄ ——> H⁺ + HSO₄^–

H⁺+ H₂O ——> H₃O⁺

WARNING:

We add acid to water. If we add water to acid, the high concentration of acid may produce a violent exothermic reaction.
Concentrated acids and bases are corrosive; no person should touch it with bare hand or skin. In case a few drops spill on the body, a person should wash it with plenty of water.

Activity 2.11

asks us to find the PH of various substance

The average PH of different food materials are the following:

saliva ph before the meal: 7.4, after the meal: depends on the food taken. if acidic food like eggs, meat, juice etc is taken ph goes down. if alkaline food is taken like vegetables, grain, ph may rise upto 8

Lemon Juice: 2.2

Colourless aerated drink: 4 carrot juice : 6

coffee: 4.5 tomato juice 4.3

tap water 6 to 8.5 1M NaoH: 14 1M HCl : 0

Activity 2.12

asks us to collect a soil sample dilute it and check the filtrate with PH paper.

OBSERVATION:Filtrate changes the colour of filter paper to green.

EXPLANATION:A PH of normal soil ranges from 5.5 to 7.5. In this ranger PH paper show green.

APPLICATION:Soil PH is an important factor in the growth of the plant. Most of the plants grow in the PH range of 5 to 7.5, adjusting the PH of soil result in the optimum output from the plant. For example, plants like apple, cauliflower, cucumber etc. grow in this PH range.

Phosphate fertilizer increases the acidity of the soil while potassium fertilizer neutralizes the PH

Activity 2.13

asks us to write the formula of various salts, their source and group them into their families.

ANSWER:

FORMULA: Potassium sulphate: K₂SO₄; Sodium sulphate: Na₂SO₄; Calcium sulphate: CaSO₄; Magnesium sulphate: MgSO₄; Copper sulphate: CuSO₄; Sodium chloride: NaCl; Sodium nitrate: NaNO₃; Sodium carbonate: Na₂CO₃; Ammonium chloride: NH₄Cl.

ACIDS AND BASES WHICH FORMS THESE SALTS:

When acids and bases mix, they react vigorously and form respective salt.

Acid + Base ———–> Respective salt

Example: Sodium hydroxide + Nitric acid ———–> Sodium nitrite

NaOH + HNO₃ ————> NaNO₃ + H₂O

ACIDS USED: Sulphuric acid (H₂SO₄); Hydrochloric acid (HCl), Nitric Acid (HNO₃), Carbonic acid (H₂CO₃).

BASES USED: Sodium Hydroxide (NaOH); Magnesium Hydroxide (Mg(OH)₂); Calcium Hydroxide (Ca(OH)₂).

FAMILY: Sodium salts: Sodium sulphate, Sodium chloride, Sodium nitrate, Sodium carbonate.

Similarly, we can group other salts as Potassium salts, magnesium salts, Ammonium Salts, Chloride salts, Sulphate salts, Nitrate salts etc

PROCEDURE:

The activity 2.14 asks us to collect some sample of various salt, check for its solubility in water, and PH of the solution formed.

ANSWER:

Solubility:

All salts of inorganic acids and inorganic bases like HCl, NaOH etc are readily soluble in water.

Salts of organic acids and organic bases are mostly insoluble in water but some may be soluble. Here only one organic salt Sodium acetate is asked which is highly soluble in water.

EXPLANATION OF SOLUBILITY:

Salts of inorganic acids are polar in nature. Polar substances dissolve in polar solvents like water. Salt of organic acids and bases are mainly non-polar in nature. They dissolve in a non-polar solution like Benzene, and carbon tera chloride.

The PH of the solution:

PH of solution = -(Log H⁺) = -log 10^-7= 7

When we add salt of a strong acid and strong base it dissociates into its ion fully and equilibrium remains the same.

NaCl ————-> Na⁺ + Cl^–

But a salt of a strong acid and a weak base ( e.g. Ammonium chloride) or salt of a weak acid and strong base (e.g. Sodium acetate) does not dissociate fully and disturb the equilibrium of water.

Activity 2.15 asks us to heat copper sulphate and then add water to it and observe the change in the colour.

OBSERVATION:

Copper sulphate is usually blue when kept in a room. On heating, copper sulphate becomes colourless and we also see a few drops in the test tube.

Now, When we add water to the test tube, copper sulphate restore its colour and become blue again.

EXPLANATION:

Copper sulphate absorbs moisture from the air and forms its hydrate (CuSO₄.7H₂O). The hydrate of copper sulphate is blue. So, we also call copper sulphate as blue vitriol.

When we heat copper sulphate its water of hydration goes away, and the substance becomes colourless.

When we add water, dehydrated copper sulphate regains its water of hydration and becomes blue.

INFERENCE:

This experiment shows that a crystal which looks solid in normal condition may not be dry as well. It may contain some other molecules attached to it. These molecules may give the crystal different physical and chemical properties like the colour.

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