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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.