acids, bases and salts · deepak sir 9811291604 acids, bases and salts 1 | p a g e acids, bases and...

Deepak sir 9811291604 Acids, Bases and Salts

1 | P a g e

Acids, Bases and Salts

About three million (30 lakh) chemical compounds are known. These compounds may be classified on the basis of their properties such as

colour, taste, solubility and chemical behaviour. The earliest classification of compounds into acids, bases and salts was primarily based on

their taste and action on litmus.

All acids have certain chemical properties in common, although there may be wide differences among some of them. Similarly, the groups

of bases and salts also share similarities. There are useful relationships between oxides and acids, between oxides and bases and between

oxides and salts.

In this chapter, you will learn about the properties and uses of acids, bases and salts, and their relationships with oxides.

NATURALLY-OCCURRING ACIDS

The naturally-occurring acids are weak acids. Many of our food items contain such weak acids in varying amounts. Such weak acids are

also present in human body and in plants. That is why, these acids are called organic acids.

Lemons, oranges, raw mangoes etc, are sour in taste due to the presence of acids in them.

Mineral acids are strong acids. Sulphuric acid (H2S04), hydrochloric acid (HCl), nitric acid (HN03) and phosphoric acid (H3PO4) are some

commonly used mineral acids. These acids are called mineral acids because these are prepared from minerals. Mineral acids are very

important from the industrial point of view. These are used in the manufacture of fertilizers, industrial chemicals, explosives, dyes and

pigments etc.

One of the mineral acids, hydrochloric acid (HCl) present in our stomach helps in the digestion of food.

Pain caused by the sting of ants, nettles and bees is due to the formic acid released by these insects.

The results of the experiment reported above shows that

all acids turns blue litmus to red , all acids turn methyl orange to red.

❖ all bases turn red litmus to blue. all bases turn phenolphthalein pink.

Many plant products contain compounds which change colour with the change in the acidic/basic nature of the medium. Some typical

examples are, Red cabbage leaves, Turmeric, Flowers of hydrangea, Petunias, Geranium. Extracts of these can also be used as acid-base

indicator.

HOME WORK

1. Name the acids present in citrus fruits.

2. Name three mineral acids.

3. What is the effect of an acid on blue litmus, red litmus and methyl orange?

4. What colour does phenolphthalein give with a base?

5. Is limewater acidic or basic?

Acids react with most metals to produce the corresponding salts and hydrogen gas is given out.

Carbonic acid does not react with metals.

Metals like sodium, magnesium, calcium react vigorously with dilute acids. Aluminium, zinc, iron, etc., react moderately with dilute acids.

The less reactive metals such as, copper, silver, gold do not react with dilute acids.

Dilute sulphuric and hydrochloric acids react with metals like magnesium and zinc to give the corresponding salt and hydrogen gas.

HOW DO ACIDS REACT WITH METALS

Less reactive and noble metals, such as, copper, silver and gold do not displace hydrogen from acids. General chemical reaction:

Metal + Acid -» Salt + Hydrogen gas

Are all hydrogen-containing compounds acids

We have seen that all acids give hydrogen gas when reacted with most metals. Thus, it appears that all acids must contain hydrogen.

Are all hydrogen-containing compounds acids? To find an answer to this question, perform the following activities.

Remarks. Ethanol and glucose are covalent compounds, and do not produce H+(oq) in solutions. So, these compounds do not show

acidic character in solutions.


2 | P a g e

HOW DO ACIDS REACT WITH METAL CARBONATES AND METAL HYDROGENCARBONATES

Acids decompose carbonates and hydrogencarbonates to give the corresponding salts and carbon dioxide gas. For example, sodium

carbonate and calcium carbonate react with hydrochloric acid and sulphuric acid to give the corresponding salts and carbon dioxide gas.

Carbon dioxide when passed through limewater, make it milky.

Genera! chemical equations

Metal carbonate + Acid--> Salt + Carbon dioxide + Water

Metal hydrogencarbonate-!- Acid -> Salt + Carbon dioxide + Water

Hydrogen ion (H+) is very small in size. Due to high charge density, it gets attached to water molecules and form hydrated ion. This

hydrated ion is simply written

HOW DO ACIDS REACT WITH METAL OXIDES

Acids react with metal oxides (basic oxides) to give the corresponding salts and water.

METAL OXIDE + ACID------------- SALT + WATER

HOW DO BASES/ALKALIS REACT WITH METALS

HOW DO BASES/ALKALIS REACT WITH OXIDES OF NONMETALS

The oxides of nonmetals are either neutral or acidic. Acidic oxides of nonmetals react with bases/alkalis to form salt and water.

HOW DO BASES/ALKALIS REACT WITH OXIDES OF NONMETALS

The oxides of nonmetals are either neutral or acidic. Acidic oxides of nonmetals react with bases/alkalis to form salt and water.

The reaction between an acid and an alkali to form a salt and water is called neutralisation reaction. A neutralisation reaction can be

described by the reaction,

WHAT DO ALL ACIDS AND BASES HAVE IN COMMON

All acids and bases give characteristic reactions. Both produce hydrogen gas when reacted with certain metals. Do all acids and bases have

something common between them?

Thus, the tendency to produce ions in their solutions in water is a common property of acids and bases/alkalis.

MORE ABOUT ACIDS AND BASES

The word acid is derived from the Latin word acidus which means

sour.

From all that has been observed from the experiments, we can say that

❖ Acids have sour taste.

❖Acids change the colour of litmus from blue to red.

❖ Acids react with certain metals liberating hydrogen gas.

Acids decompose carbonates and hydrogencarbonates giving out

carbon dioxide gas. Acids neutralise bases to give salt and water.

On the other hand, the substances having the following properties

are considered bases:

❖ Bases have bitter taste.

❖ Bases are slippery to touch.

❖ Bases change the colour of litmus from red to blue.

❖ Bases neutralise acids to form salt and water.


3 | P a g e

A systematic classification, however, began with the concept put forwarded by Svante Arrhenius in 1887.

What are acids and bases

Acids and bases may be defined as follows:

□ An acid is a hydrogen-containing compound which gives free hydronium ions (H30+ or H+ (aq)) when dissolved in water.

Thus, hydrogen chloride (HCL), acetic acid (CH3COOH) and sulphuric acid (H2S04), are acids because all these compounds give free H30+

(or H+(aq)) ions in aqueous solutions.

□ A base is a compound which gives free hydroxide ions (OH ) when dissolved in water.

Thus, the compounds, such as NaOH, KOH, CaO and NH4OH are bases, because these compounds give free OH" ions in aqueous solutions.

What are strong and weak acids The acids which are almost completely ionised when dissolved in water are called strong acids.

Hydrochloric acid (HCI), sulphuric acid (H2S04), nitric acid (HNO3), perchloric acid (HC104) are strong acids. The solutions of strong acids in

water are highly conducting due to high concentration of hydrogen ion (H+) in the solution.

The acids which are partially ionised when dissolved in water are called weak acids.

Acetic acid (or ethanoic acid, CH3COOH), carbonic acid (H2C03), hydrocyanic acid (HCN), sulphurous acid (H2S03), hydrogen sulphide

(H2S) are weak acids.

Phosphoric acid (H31'0.() and oxalic acid (H2C204 or (COOH)2) are moderately weak acids.

Strong acids are also strong electrolytes. Weak acids are also weak electrolytes.

The words 'strong' and 'weak' refer to the degree of ionisation of the acid or base in their solutions, and is nothing to do with their

concentration in the solution.

The solutions of weak acids in water are poorly conducting due to low concentration of H30+ (or H+) ions in them.

What are strong bases (or alkalies) and weak bases

□ Bases which are almost completely dissociated/ionised in their solutions are called strong bases. Strong bases are also called alkalis.

Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are strong bases (or alkalis). Solutions of strong bases (or alkalis) are highly

conducting because they contain high concentration of OH- ions.

□ Bases which are partially dissociated/ionised in their aqueous solutions are called weak bases.

Ammonium hydroxide (NH4OH), calcium hydroxide (Ca(OH)2) magnesium hydroxide (Mg(OH)2) are weak bases.

Solutions of weak bases are very poorly conducting because they contain very low concentration of OH- ions.

What is meant by concentrated and dilute acids

All acids are the solutions of acidic gases in water.

❖ A solution that contains the maximum amount of the acidic gas is called concentrated acid.

❖ A solution containing lesser amount of the acidic gas (i.e., larger amount of water) is called dilute acid. The degree of dilution may be

mentioned as moderately dilute, dilute, very dilute or very-very dilute acid.

In practice, dilute acid is prepared by adding the required amount of concentrated acid into a calculated amount of water.

Why is the concentrated acid added into water and not water to the acid while preparing a dilute solution of an acid from concentrated

acid

Dissolution of a concentrated acid or a base, particularly concentrated sulphuric acid and solid sodium hydroxide, is a highly exothermic

reaction.

When water is added to a concentrated acid, the heat liberated is so large that the solution starts almost boiling. This may cause spurting of

the hot acid solution and harm the person. Excessive local heating may even break the glass container.

That is why, concentrated acids and bases are diluted by slowly adding concentrated acid or base into water with constant stirring.

What are the uses of acids

Hydrochloric, nitric and sulphuric acids are very important acids from the commercial point of view.

Some important uses of these acids are mentioned below:


4 | P a g e

HOW STRONG ARE THE SOLUTIONS OF ACIDS/BASES

The strength of any solution of an acid or a base can be determined from the concentration of H+(aq) or OH~(aq) in the solution. It is

commonly described in terms of a parameter called pH. This is discussed below:

What is meant by the pH of a solution

A Danish biochemist S.P. Sorensen (1909) proposed that the strength of acidity of a solution be expressed in terms of a parameter called pH.

According to him, pH of a solution is defined as the negative logarithm (to the base 10) of the hydrogen ion concentration in the solution.

Mathematically,

pH = - log [H+] = log[1/H+]

The pH values in aqueous solutions usually vary from 0 (highly acidic) to 14 (highly alkaline).

Relationship between pH values and the acidic or basic nature of any aqueous solution (at 298 K)

What are the uses of ACID

❖ Hydrochloric acid (HCI)

❖ For removing deposits from inside the boilers. This

process is called descaling.

❖ For preparation of chlorides and chlorine gas,

❖ For cleaning iron sheets before galvanization,

❖For extracting glue from bones,

❖In textile industry for dyeing.

❖ For cleaning kitchen sink and sanitary wares.

❖ Nitric acid (HNO3) ❖ For preparing fertilizers, explosives, dyesand drugs.

❖ In the refining of gold and silver.

❖ For cleaning gold and silver ornaments.

❖ Sulphuric acid (H2S04)

❖ For preparing fertilizers, detergents, plastics,

synthetic fibres

❖ In petroleum industry for refining,

❖ In lead-acid batteries (batteries used in cars, trucks,

buses etc.) as electrolyte.

What are the uses of bases

The uses of some typical basesare described below:

❖ Sodium hydroxide (caustic soda) (NaOH)

❖ In soap and detergent industry.

❖ For the manufacture of rayon. .

❖ In paper and pulp industry.

❖ For manufacturing other chemicals.

Calcium hydroxide (slakedlime) [Ca(OH)2]

❖ For whitewashing.

❖ For the manufacture of bleaching powder.

❖ In leather industry.

❖ For neutralising acidity of the soil.

❖ For softening hard water.

❖ As an insect/pest killer.

❖ Ammonium hydroxide (NH4OH) ❖ As a cleansing agent.

❖ For preparing ammonium salts.

❖ For manufacturing fertilizers, nylon and nitric acid

❖ Aluminium hydroxide |AI(OH),|

❖ For preparing antacids. In textile industry.

Acidic, neutral and basic character of solutions and the pH

The nature of an aqueous solution depends upon the relative concentrations of H+ and OH" ions in it. If,

❖ [H+] = [OH-], then the solution is said to be neutral.

❖ [H+] > [OH-], then the solution is said to be acidic.

❖ [H+] < [OH-], then the solution is said to be alkaline or basic.

At 25°C, (298 K)

❖ For pure water or a neutral solution: pH = 7.0

❖ For an acidic solution: pH < 7.0

❖ For an alkaline solution: pH > 7.0

Thus, at 298 K,

❖ The pH values over the range 0 to 7 lie on the acidic side of the pH scale.

❖ The pH values over the range 7 to 14 lie on the alkaline (or basic) side of the pH scale.

What is the importance of pH in everyday life

The concentration of hydrogen ion, and therefore, pH has marked effect on animal and plant life. Some

major fields of its applications are described below:

❖ The pH in our digestive system. pH plays a vital role in the digestion of food and other biochemical

reactions inside the human/animal body. The pH of the gastric juice is 1-2 due to the secretion of

hydrochloric acid in stomach. During ingestion, the stomach produces more acid. This excess acid causes

irritation. This is commonly called acidity. To have relief from acidity, we generally take antacids.

Antacids neutralise the excess acid. Commonly used antacids contain aluminium hydroxide or

magnesium hydroxide.


5 | P a g e

MORE ABOUT SALTS

What are salts

Salt is the product of a neutralisation reaction between an acid and a base.

For example, sodium chloride formed in the reaction between sodium hydroxide and hydrochloric acid is a salt.

NaOH + HCI -------> NaCl + HzO NH4OH + HCI -------------> NH4C1 + HzO Alkali ncid salt water base acid salt water

In the above reactions, hydrogen ion of an acid is replaced by a metal ion or ammonium ion. Thus, a salt may also be defined as the

compound formed when the hydrogen ion of an acid is replaced by a metal ion or an ammonium ion.

Salts are formed by the reaction between an acid and a base.

HA + MOH ------------> M+A" + H20 Acid base/ alkali

The parent acids and bases of some salts are identified as follows:

Thus, the cation of the salt come from the base and the anion of the salt from the acid. Therefore, name of any salt is derived from the names

of the cation and the anion present in it.

How to write the name of a salt

Follow the following steps to name a salt:

❖ Write the name of the metal ion (cation) or ammonium ion (NH4+) coming from the base/alkali.

❖ Write the name of the anion coming from the acid on the right of the metal or ammonium ion. For example, the salt

NaCl is named as Sodium chloride

Na2S04 is named as Sodium sulphate

Na2C03 is named as Sodium carbonate

in an acid-base reaction, M+

(metal ion, a cation) of the base

replaces hydrogen ion (H+) of

the acid.

(the salt contains M+ (cation)

coming from the base and A"

(anion) coming from the acid.

❖ pH of blood is maintained within the range of 7.36 to 7.42. This is due to the buffer action of bicarbonate-

carbonic acid system.

❖ Enzymes function effectively only at certain pH, e.g. trypsin acts best at an alkaline pH.

❖ The control of pH values is very important from the point of view of analytical chemistry. This permits

selective detection, identification and/ or isolation of certain substances in the presence of others.

❖ The pH change as the cause of tooth decay. The tooth enamel, made up of calcium phosphates, is the

hardest material in our body. It does not dissolve in water. It gets corroded at pH below 5.5, i.e., in moderately

acidic conditions. The bacteria produce acid during the degradation of sugar and the food particles left behind

after meals (if not properly cleaned). This acid corrodes the teeth. To prevent tooth decay, one should brush

teeth properly after each meal. Another way to prevent tooth decay is to avoid eating sugary foods.

❖ Control of pH of the soil. Plants also need a specific pH range for proper growth. The soil may be acidic,

basic or neutral depending upon the relative concentration of H+ and OH~. The pH of any soil can be

determined by using pH paper.] Toothpastes are slightly basic. So, they neutralise the excess acid around teeth.

Honeybee sting and Nettle sting release methanoic acid, (formic acid). This causes pain and irritation. Rubbing a

mild base such as baking soda (sodium hydrogencarbonate) over the affected area gives relief.


6 | P a g e

NaHC03 is named as Sodium hydrogencarbonate

K2S03 is named as Potassium sulphite

CH3COONa is named as Sodium acetate (or Sodium ethanoate)

NH4C1 is named as Ammonium chloride

(NH4)2S04 is named as Ammonium sulphate

CuS04 is named as Copper sulphate

What is meant by a family of salts

The salts having the same positive radical (or cation) or negative radical (or anion) are said to belong to the same family. For example,

❖ NaCl (sodium chloride) and Na2S04 (sodium sulphate) belong to the family of sodium salts because both contain the same radical (or

cation), that is Na+. These may be called sodium salts.

❖ Copper sulphate (CuS04) and sodium sulphate (Na2S04) belong to the family of sulphates because both contain the same acid radical (or

anion), that is sulphate (S042_).

The salts belong to certain families are listed below:

How are salts classified

Salts can be classified into the following categories:

□ Normal salts. When all the replaceable hydrogen atoms in an acid molecule are replaced by metal ions, the salt formed is called normal

salt. Sodium chloride (NaCl), sodium sulphate (Na2S04), calcium carbonate (CaC03), sodium carbonate (Na2C03) are normal salts.

□ Acidic salts. The salt obtained by partial replacement of ionisable hydrogen atoms in an acid molecule by metal ions is called an acidic

salt. For example, the salts formed in the following reactions are acid salts.

H2S04 + NaOH ---------> NaHS04 + HzO sulphuric acid sodium hydroxide sodium hydrogensulphnte

□ Basic salts. The salt which contains one or more hydroxyl groups (coming from the base) alongwith the anion coming from the acid is

called a basic salt. Some examples of basic salts are:

Pb(OH)Cl Lead hydroxychloride (Basic lead chloride)

CuC03 • Cu(OH)2 Basic copper carbonate (Malachite) Ca(OH)Cl Calcium hydroxychloride

Basic salts are obtained when the reaction between a base and acid is carried out in almost neutral solution.

SOLUBILITY OF SALTS IN WATER

Salts differ considerably in their solubility in water.

❖ Salts of sodium, potassium are soluble in water.

❖ Salts of silver, mercury, lead etc, are almost insoluble in water.

❖ Some salts of calcium, magnesium and barium are highly soluble, whereas some others are almost insoluble in water.

Solubility of some salts in water is given in


7 | P a g e

THE pH OF SALT SOLUTIONS

Salts are ionic compounds. Almost all salts are solid at room temperature. So, there is no way to measure the pH of salts. In fact, we can

only measure the pH of salt solutions in water. The pH of any salt solution can be determined by using a pH paper or a pH metre.

Litmus paper or litmus solution can also be used to know about the acidic or basic/alkaline nature of any salt solution. The acidic or

basic nature of certain salt solutions is mentioned .

The pH of a salt solution can be predicted from the nature of parent acid and base/alkali

The results of pH determination can be summarised as follows:

❖ The solution of the salt of a strong acid and strong base is neutral.

❖ The solution of the salt of a strong acid and weak base is acidic.

❖ The solution of the salt of a weak acid and strong base is basic.

What are the uses of salts

Each salt has many uses. Uses of some commonly used salts are given below:


8 | P a g e

CHEMICALS FROM COMMON SALT

Common salt is an ionic compound of sodium and chlorine. Chemically, common salt is sodium chloride. Highly purified sample of

common salt is called sodium chloride. Its simplest formula is NaCl. In fact, sodium chloride exists as an aggregate represented by the

formula (Na+Cl-)„.

The main source of common salt (sodium chloride) is the sea water. Sea water contains about 3.5% of soluble salts, the most common of

which is sodium chloride (2.7 to 2.9%). Saline water of inland lakes, such as Sambhar lake in Rajasthan is also a good source of common salt.

Common salt (sodium chloride) is also found as rock salt. Beds of rock salt were formed when lakes/seas dried up in past.

Why is common salt considered a raw material for chemicals

We can obtain many useful substances/chemicals from common salt. Thus, the common salt is the raw material for many chemicals. Some

commonly used substances which can be obtained from common salt are,

♦ Sodium hydroxide (NaOH)

♦ Bleaching powder (CaOCl2)

❖ Sodium hydrogencarbonate (NaHC03) - also called sodium bicarbonate or baking soda

❖ Sodium carbonate (Na2C03) - also called washing soda.

SODIUM HYDROXIDE

Commercially, sodium hydroxide is also called caustic soda because of its corrosive action on animal and vegetable tissues.

How is sodium hydroxide obtained from common salt

Sodium hydroxide is prepared by the electrolysis of 20% common salt solution, (called brine). This process is called chlor-alkali process

because of the products formed — chlorine (as a bye-product) and sodium hydroxide (an alkali).

When electricity is passed through brine (20% common salt solution), the following reactions take place.

sodium amalgam then reacts with water to give sodium hydroxide (NaOH) and hydrogen gas (H2).

What are the by-products obtained during the preparation of sodium hydroxide

The electrolysis of common salt solution gives the following products,

❖ Sodium hydroxide (NaOH) (Main product)

❖ Chlorine (Cl2) (By-product)

❖ Hydrogen (H2) (By-product)

These chemicals are very important from industry point of view.

The main uses of sodium hydroxide, chlorine and hydrogen are listed


9 | P a g e

BLEACHING POWDER

Chemically, bleaching powder is calcium oxychloride, CaOCl2 or Ca(OCl)Cl. Bleaching powder is also called chloride of lime.

How is bleaching powder prepared

Bleaching powder is prepared by the action of chlorine on slakedlime.

Ca(OH)2(s) + Cl2(g) --------------> CaOCl2(s) + H20(l)

Slakedlime chlorine bleaching powder

How is bleaching powder manufactured

Bleaching powder is manufactured by the action of chlorine on dry slakedlime at 35°C. The .reaction is,

Ca(OH)2(s) + Cl2(g) -> CaOCl2(s) + H20(l)

Slakedlime chlorine bleaching powder

What are the properties of bleaching powder

Some typical properties of bleaching powder are given below:

❖ Colour and odour. Bleaching powder is a yellowish-white powder which strongly smells of chlorine.

❖ Solubility in water. It is soluble in cold water. The unreacted lime present in it, however, remains undissolved.

❖ Exposure to air. When exposed to air, bleaching powder gradually loses its chlorine. This is due to the reaction of atmospheric C02

with bleaching powder.

CaOCl2(s) + C02(g) ----------> CaC03(s) + Cl2(g)

❖ With acids. Bleaching powder is decomposed by dilute acids to give off Cl2 gas. With HCI and H2SO4,

CaOCl2 + 2HCl(dil.) -> CaCl2(aq) + H20(Z) + Cl2(g)

CaOCl2(s) + H2S04(dil.) -> CaS04(s) + H20(Z) + Cl2(g)

❖ With water. It is partially soluble in water due to the presence of unreacted lime in it. With water, it gives oxygen gas.

2CaOCl2(s) + H20(/) -> 2CaCl2(aq) + H20(Z) + 02(g)

What are the uses of bleaching powder Bleaching powder is used for the following purposes:

❖ Bleaching cotton fibre/fabrics in textile industry and wood pulp in paper industry

❖ As a disinfectant and germicide

❖ Sterilizing drinking water

❖ As an oxidising agent

BAKING SODA (or SODIUM HYDROGENCARBONATE)

The chemical name of baking soda is sodium hydrogencarbonate or sodium bicarbonate. Baking soda (or sodium bicarbonate) is

represented by the formula NaHC03

How is baking soda prepared

In laboratory, sodium hydrogencarbonate (baking soda) can be prepared by saturating a cold solution of sodium carbonate with carbon

dioxide.

Na2C03(aq) + C02(g) + H20(Z) -> 2NaHC03

sodium carbonate carbon dioxide sodium hydrogencarbonate

(white crystals)

Sodium hydrogencarbonate being less soluble, separates out as white crystals.

How is baking soda manufactured

Sodium bicarbonate is obtained as an intermediate product in the Solvay's process for the manufacture of sodium carbonate from common

salt . The basic reaction is, NaCl(acj) + HzO(l) + C02(g) + NH3(g)----------- -> NH4Cl(aq) + NaHC03(s)

Hydrogen

As a fuel in rockets and fuel cells For

the manufacture of Ammonia — used

for making fertilisers

Chlorine

For water treatment

For the manufacture of PVC

For manufacturing pesticides

For manufacturing bleaching powder

Sodium hydroxide

For degreasing metal sheets/rods etc.

For manufacturing soaps and

detergents

In the synthesis of artificial fibres,

paper etc.

In textile industry

Hydrochloric acid

For cleansing iron/steel surfaces

As a laboratory reagent

For manufacturing ammonium chloride

Sodium hypochlorite

As a household bleach


10 | P a g e

What are the properties of baking soda

Some common properties of baking soda are described below:

□ State and solubility. Sodium bicarbonate (baking soda) is a white crystalline substance. It is sparingly soluble in water.

□ With water. Aqueous solution of sodium bicarbonate is mildly alkaline (or basic), due to the hydrolysis of HC03" ion. Sodium bicarbonate

solution becomes basic due to the presence of OH" ions but does not give pink colour with phenolphthalein because it is mildly basic.

What are the uses of baking soda (sodium bicarbonate)

Some typical uses of sodium bicarbonate (baking soda) are given below:

❖ Sodium bicarbonate is used for preparing baking powder and effervescent drinks.

❖ Sodium bicarbonate is used as an antacid. It corrects acidity in the stomach.

❖ Sodium bicarbonate is used in soda-acid type fire extinguishers.

What is baking powder

Baking powder is used for preparing porous, fluffy cakes, bread, etc. Baking powder is a mixture containing baking soda (sodium

bicarbonate, NaHC03) and an acidic compound, such as potassium hydrogentartarate or citric acid. During the preparation of cake/bread,

baking soda (sodium bicarbonate) reacts with the acidic compound to liberate carbon dioxide. The carbon dioxide (C02) so released makes

the cake/bread porous and fluffy (light weight and soft). NaHC03(aq) + H+(aq) -> C02(g) + H20(Z) + Sodium salt of the acid.

WASHING SODA for SODIUM CARBONATE)

The chemical formula of washing soda is Na2CO3-10H2O, (sodium carbonate decahydrate). Anhydrous sodium carbonate (Na2C03) is

generally called soda ash

How is sodium carbonate manufactured: Solvay Process

Sodium carbonate (or washing soda) is obtained on commercial scale by Solvay's process.

The raw materials used in the manufacture of sodium carbonate are,

♦ Sodium chloride (NaCl) in the form of its concentrated solution called brine

♦ Ammonia (NH3)

♦ Limestone (CaC03)

In this process, ammonia gas is bubbled through a concentrated solution of sodium chloride (called brine). The ammoniacal solution of

sodium chloride (or brine) is pumped up to the top of the carbonating tower. Carbon dioxide gas is introduced into the carbonating tower

through an inlet near its base. The ammoniacal brine percolating down from the top absorbs the upcoming carbon dioxide.

What are the physical properties of washing soda Physical properties of washing soda are given below:

□ Colour, form and solubility. Washing soda (Na2CO3-10H2O) is a white crystalline solid. It readily dissolves in water.

□ Efflorescence. When exposed to dry air, it loses molecules of water of crystallisation to give white powder having a composition

Na2C03H20.

What are the physical properties of washing soda Physical properties of washing soda are given below:

□ Colour, form and solubility. Washing soda (Na2CO3-10H2O) is a white crystalline solid. It readily dissolves in water.

□ Efflorescence. When exposed to dry air, it loses molecules of water of crystallisation to give white powder having a composition

Na2C03H20.

Washing soda undergoes efflorescence to give white powder of sodium carbonate monohydrate, (Na2C03-H20).

□ Action of heat. On heating strongly, washing soda gives anhydrous sodium carbonate (soda ash).

What are the uses of washing soda (or sodium carbonate)

Some uses of washing soda are given below:

❖ Washing soda (or sodium carbonate) is used for washing clothes (laundry purposes).

❖ Washing soda is used for softening hard water.

❖ Sodium carbonate (soda ash) is used for the manufacture of detergents.

❖ Sodium carbonate is used for the manufacture of many important compounds, such as borax (Na2B407), hypo (Na2S203-5H20), etc.

♦:♦ Sodium carbonate is also used in paper and paint industries.

ARE THE CRYSTALS OF SALTS REALLY DRY

Crystals of some salts contain certain amount of associated water. The water associated with the crystal (or molecule) of any salt is called

water of crystallisation.

The salts containing water of crystallisation are called hydrated salts. Some typical salts which contain water of crystallisation are,

acids, bases and salts · deepak sir 9811291604 acids, bases and salts 1 | p a g e acids, bases and...

Documents