acids,base and salts

Acids,Baseand Salts

Unit -072ND Term

AcidsPhysical properties of the acids

Having sour taste.

1.What is an acids?

An acid is a compound that releases hydrogen ions (H+) in an

aqueous medium.

Based on the strength of

releasing H+ ions in the

aqueous medium, acids are

classified as,

1.Strong acids 2.Weak acids.

Acids in school laboratory

Weak acids

2.What is a strong acid?

The acids that release H+ ions by complete ionization in

aqueous medium are strong acids.

3.What is the meaning of “complete ionization in

aqueous medium are strong acids”?

It means that all such acid molecules are dissociated into H+ ions

and the corresponding negative ions in water.

HCl(aq) H+ + Cl-

Based on the strength of releasing H+ ions

in the aqueous medium, acids are

classified as,

1.Strong acids and 2.Weak acids.

Strong acids

The acids that release H+ ions by completeionization in aqueous medium are strongacids.

Other ions – As water use to prepare the

solution,it contains H20 and OH-

Ionization of acids

H2SO4(aq) 2H+(aq) + SO-2

(aq)

1mol 2 mol 1mol

6.022x 1023 2x6.022x 1023 6.022x 1023

Nitric acid (HNO3) –

HNO3(aq) H+(aq) + NO3 (aq)

Nitric acid (HNO3) –

HNO3(aq) H+(aq) + NO3 (aq)

1mol 1 mol 1mol

6.022x 1023 6.022x 1023 6.022x 1023

Hydrochloric acid (HCl)

HCl (aq)H+

(aq) + Cl- (aq)

In a solution of hydrochloric acid which is a strong

acid, there are only H+ ions and Cl- ions but no

free HCl molecules.

The acids which release H+ ions in

aqueous medium by incomplete or partial

ionisation are called weak acids.

This means that in aqueous medium, only a fraction of such acid

molecules are dissociated into H+ ions and relevant negative

ions.

The unionized molecules remain as molecules themselves in

aqueous solution.

unionised molecules

Carbonic acid, (H2CO3), a compound of the elements

hydrogen, carbon, and oxygen.

It is formed in carbon dioxide (CO2), dissolves in water.

Most of the acids in laboratory stores areconcentrated acids.Prepare dilute acid from concentrated acids

Mixing such concentrated acids withwater.

Acids of low concentration are known as

dilute acids.

Uses of some acids

Hydrochloric acid

1.Removal of rust in steel objects

2.Making gelatin from bony materials in food technology

3. Making aqua regia ( aqua regia is a mixture of concentrated

nitric acid and concentrated hydrochloric acid mixed in the

proportion of 1 : 3.

Aqua regia is used to dissolve metals like gold and

platinum)

Sulphuric acid

1.Production of fertilizers such as ammonium sulphate and

triple superphosphate

2. Making battery acid (Battery acid is diluted sulphuric

acid)

3. Production of paints, plastics and detergents

4.Concentrated sulphuric acid is used as a dehydrating agent

5.Drying gases (For drying a gas, the relevant gas is bubbled

through concentrated sulphuric acid)

Acetic acid

1.Processing food where vinegar is used

2. Coagulation of rubber latex

3.Production of photographic films

4. Used in the paper industry

5. Production of synthetic threads in textile

industry

BasesMilk of magnesia, toothpaste, soap and lime are

examples for bases.

Many bases are solids

Sodium hydroxide (NaOH)

Potassium hydroxide (KOH)

Calcium hydroxide (Ca(OH)2)

Ammonia is a gas showing basic properties

NH3

Bases frequently used in the

laboratory.

1.Sodium hydroxide (NaOH)

2.potassium hydroxide (KOH)

3.Ammonia solution (NH4OH)

What is base?A base is a chemical compound that increases the hydroxyl

ion (OH-) concentration of an aqueous solution.

NaOH (aq) Na+ (aq) + OH- (aq)

Solution are colorless

The bases that completely ionise in

aqueous solution are called strong

bases.

The bases which partially ionise in

aqueous solution are known as weak

bases.

Ex : Ammonia solution (NH4OH)

Sodium hydroxide

1. Production of soap, paper, artificial silk and paints

2. Used in the laboratory as a strong base

3. Refining petroleum products

Magnesium hydroxide

1. Magnesium hydroxide suspension (milk of magnesia) is used as an

antacid to relieve gastritis (acidity in stomach)

2. Purification of molasses in sugar industry

Uses of the bases

Properties of acids and bases

Identification of acids and bases by indicators

Chlorine gas

Chlorine gas decolourize any wetobjects such as red or blue litmus.

Litmus papers

Red litmus turns to blue by base

Blue litmus turns to red by base

NO colour change of any litmus paper.

Methyl orange

Phenolphthalein

pH indicator

pH papers

Like the litmus papers, these are available in the form of

books or rolls in the laboratory.

These have been prepared by mixing several indicators.

The pH scale is used to indicate how acidic or basic a

given solution is.

The scale generally consists of a series of numbers

from 0 to 14.

Each number corresponds to a colour

How does pH indicator are used?

The pH value can be found by dipping a

pH paper in the relevant solution and

comparing the colour of the paper with

the colour code.

Salts

The common salt (NaCl) that we use in

our day to day life is a salt.

The Jeewani solution given during ailing conditions

such as diarrhoea and the saline solution given to

patients are mixtures containing salts.

The salts formed by the reaction between a strong

acid and a strong base show neutral properties.

Explain the “neutralization”.

Neutralization is the combination of H+ ions

released by an acid with OH- ions released

by a base to form water molecules.

When an acid reacts with a base their acidic properties

as well as the basic properties disappear.

pH value is 7

About neutralization reaction

About salts

1.Ionic compounds

Ex -

Applications of the acid - base neutralization reactions

1.Milk of magnesia is used to neutralize the acidity in

the stomach.

2.Wasp sting is basic -lime juice or vinegar on the place of

sting reduces the venomous nature as well as the pain.

3.Bee sting is acidic - By applying a weak basic substance

such as baking soda (NaHCO3) or calcium carbonate

(CaCO3) on the place of the sting, the pain is relieved.

4. Add basic substances such as ash and quicklime (calcium

oxide) to soil to reduce soil acidity.

1.i.What are the observation of the following instances?

a-Dissolve NaOH in water

It can be observed that when solid sodium hydroxide dissolves in water

the temperature rises.

Solution is colourless.

.

What is the reason for the increase in temperature when solid

sodium hydroxide dissolves in water?

The temperature increases because of the loss of heat.

Explain the reason for the above instances.

Dissolve ammonium chloride(NH4Cl) in water

•When solid ammonium chloride dissolves in water,

the temperature falls.

Temperature decreased because of the absorption of heat.

Heat changes occurring in a chemical reaction,Reaction of magnesium metal with dilute hydrochloric acid

Observation

The temperature has increased.

Evolve air bubbles. Mg strip is dissolved

That means, when this reaction happens heat is

lost.

The reason for the evolution of heat in

an exothermic reaction is that the

energy contained in the products is less

than the energy content of the reactants.

The chemical reactions happening with the evolution

of heat are called exothermic reactions.

Exothermic reactions can be represented simply as

follows.

An exothermic reaction can be illustrated byan energy level diagram

Reactants

Products

Energy

Energy

released

Endothermic reactionReaction of Sodium Carbonate with Citric acid

When the reaction between citric acid and sodium

bicarbonate occurs, the temperature decreases.

The reason for this decrease in temperature is the

absorption of heat during the reaction.

The reactions taking place with the absorption

of heat are known as endothermic reactions.

The reason for the absorption of heat during an

endothermic reaction is the fact that the energy

in the products is greater than the energy in the

reactants.

Energy level diagram for the endothermicreaction

Reactants

Products

Energy

absorbed

Find the energy change of a chemical reaction quantitatively.

Experimental determination of the heat change of the

reaction between sodium hydroxide (NaOH) and

hydrochloric acid (HCl)

1.50 cm3 of 2 mol dm-3 sodium hydroxide solution

2.50 cm3 of 2 mol dm-3 hydrochloric acid solution

3.Two 100 cm3 beakers

4.A thermometer of range 0-100 0C

5.A polystyrene cup, a glass rod

Calculation

Measure the initial temperatures of the two solutions.

After measuring the temperature of the solution

of the base, wash the thermometer before

measuring the temperature of the acid solution.

Mix these two solutions in

a polystyrene cup,

stir with the glass rod

and record the maximum

temperature.

Now we have two temperatures.

1.Initial temperature of

HCl and NaOH

2.Maximum temperature of the solution

Find the temperature difference

This calculation is based on the assumption

1.That the entire quantity of heat of the reaction

between sodium hydroxide and hydrochloric acid is

used to raise the temperature of 100 cm3 of the

solution.

2.That the specific heat capacity of the

solution is equal to that of water.

3.The density of the solution is equal to that

of water.

40 cm3 of a vinegar (dilute acetic acid) solution was mixed with 60

cm3 of a very dilute solution of lime water.(calcium hydroxide)

Then, the temperature of the mixture increased by 10 0C

i. Calculate the heat change occurred during the above reaction.

Examples for exothermic reactions

Burning of fuels

Cellular respiration

Netralization reactions

Acids base reactions

In the production of slaked lime.,

Examples for endothermic reactions

Photosynthesis reaction

Thermal decomposition reactions.