.A liquid aerosol is a colloidal system of:
1. a liquid dispersed in a solid
2. a liquid dispersed in a gas
3. a gas dispersed in a liquid
4. a solid dispersed in a gas
.
.Subtopic: Colloidal Solution
Answer ▽ ✅Verified
2. a liquid dispersed in a gas
➡️Classification Based on Physical State of Dispersed Phase and Dispersion Medium
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.Negative catalyst or inhibitor is one:
1. which retards the rate of reaction
2. takes the reaction in forward direction
3. promotes the side reaction
4. none of the above
.
.Subtopic: Catalyst
Answer ▽ ✅Verified
1. which retards the rate of reaction
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.Clouds, mist, fog and aerosols are colloidal solution of:
1. solid in a gas
2. gas in a solid
3. liquid in a gas
4. gas in a liquid
.
.
Answer ▽ ✅Verified
3. liquid in a gas
➡️Classification Based on Physical State of Dispersed Phase and Dispersion Medium
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.The charge on As2S3 sol is due to the adsorption of:
1. H+
2. OH-
3.
4. S2-
.
.
Answer ▽ ✅Verified
4. S2-
The negative charge on sol particles
is due to the preferential adsorption of on
the surface of sol particles.
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.Platinized asbestos used as a catalyst in the manufacture of H2SO4 is an example of:
.1. heterogeneous catalyst
2. auto-catalyst
3. homo-catalyst
4. induced catalyst
.
Answer ▽ ✅Verified
1. heterogeneous catalyst
A catalyst is a substance which enhances the rate of a chemical reaction without
itself getting used up in the reaction. The phenomenon using catalyst is known as
catalysis. In homogeneous catalysis, the catalyst is in the same phase as are the
reactants, and in heterogeneous catalysis the catalyst is in a different phase from
that of the reactants.
itself getting used up in the reaction. The phenomenon using catalyst is known as
catalysis. In homogeneous catalysis, the catalyst is in the same phase as are the
reactants, and in heterogeneous catalysis the catalyst is in a different phase from
that of the reactants.
Heterogeneous catalysis: Adsorption of reactants on the solid
surface of the catalysts increases the rate of reaction. There are
many gaseous reactions of industrial importance involving solid
catalysts. Manufacture of ammonia using iron as a catalyst,
manufacture of H2SO4 by contact process and use of finely divided
nickel in the hydrogenation of oils are excellent examples of
heterogeneous catalysis.
The catalytic process in which the reactants and the catalyst are in
different phases is known as heterogeneous catalysis. Some of the
examples of heterogeneous catalysis are given below:
(i) Oxidation of sulphur dioxide into sulphur trioxide in the
presence of Pt.
Pt(s)
2SO₂ (g) +Pt(s)→ 2SO₃ (g) 2
The reactant is in gaseous state while the catalyst is in the
solid state.
(ii) Combination between dinitrogen and dihydrogen to form
ammonia in the presence of finely divided iron in Haber’s process
The reactants are in gaseous state while the catalyst is in the
solid state.
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.In a reversible reaction, a catalyst:
.1. increases the rate of the forward reaction only
2. increases the rate of the forward reaction to a greater extent than that of the backward reaction
3. increases the rate of the forward reaction and decreases that of the backward reaction to the different extent
4. increases the rate of the forward and backward reactions equally
.
Answer ▽ ✅Verified
4. increases the rate of the forward and backward reactions equally
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.Gas masks containing activated charcoal to remove poisonous gases from atmosphere acts on the principle of:
1. adsorption
2. absorption
3. sorption
4. all of these
.
.
Answer ▽ ✅Verified
1. adsorption
Being highly
porous, activated charcoal is used in
adsorbing poisonous gases; also used in water
porous, activated charcoal is used in
adsorbing poisonous gases; also used in water
filters to remove organic contaminators and in
air conditioning system to control odour.
Gas masks: Gas mask (a device which consists of activated charcoal
or mixture of adsorbents) is usually used for breathing in coal
mines to adsorb poisonous gases.
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.Tanning of leather is:
1. coloring of leather by chemicals
2. drying process to make the leather hard
3. polishing of leather to make it look attractive
4. coagulative hardening of the leather by chemicals
.
.
Answer ▽ ✅Verified
4. coagulative hardening of the leather by chemicals
Tanning: Animal hides are colloidal in nature. When a hide, which
has positively charged particles, is soaked in tannin, which contains
negatively charged colloidal particles, mutual coagulation takes
place. This results in the hardening of leather. This process is
termed as tanning. Chromium salts are also used in place of tannin.
has positively charged particles, is soaked in tannin, which contains
negatively charged colloidal particles, mutual coagulation takes
place. This results in the hardening of leather. This process is
termed as tanning. Chromium salts are also used in place of tannin.
According to Rigveda, tanning of leather
and dying of cotton were practised during
1000–400 BCE.
Calcium Hydroxide (Slaked lime), Ca(OH)2
Calcium hydroxide is prepared by adding
water to quick lime, CaO.
It is a white amorphous powder. It is
sparingly soluble in water. The aqueous
solution is known as lime water and a
suspension of slaked lime in water is known
as milk of lime.
When carbon dioxide is passed through
lime water it turns milky due to the formation
of calcium carbonate.
On passing excess of carbon dioxide, the
precipitate dissolves to form calcium
hydrogencarbonate.
Milk of lime reacts with chlorine to form
hypochlorite, a constituent of bleaching
powder.
It is used in glass making, in tanning
industry, for the preparation of bleaching
powder and for purification of sugar.
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.Hardy-Schulze rule states that:
1. non-electrolytes have better coagulating action on colloids than electrolytes
2. sols are coagulated by effective ions whose charge is opposite to that of sol and the ions of higher charge are much more effective than the ions of lower charge
3. charge of the ions has no effect on the coagulation of a sol
4. sols are coagulated only by those ions whose charge is similar to that of the sol
.
.
Answer ▽ ✅Verified
It has been observed that, generally, the greater the valence of the
flocculating ion added, the greater is its power to cause precipitation.
This is known as Hardy-Schulze rule. In the coagulation of a negative
sol, the flocculating power is in the order: Al3+>Ba2+>Na+
Similarly, in the coagulation of a positive sol, the flocculating power
is in the order: [Fe(CN)₆]⁴⁻ > PO4³⁻ > SO4²⁻ > Cl–
The minimum concentration of an electrolyte in millimoles per litre
required to cause precipitation of a sol in two hours is called coagulating
value. The smaller the quantity needed, the higher will be the coagulating
power of an ion.
flocculating ion added, the greater is its power to cause precipitation.
This is known as Hardy-Schulze rule. In the coagulation of a negative
sol, the flocculating power is in the order: Al3+>Ba2+>Na+
Similarly, in the coagulation of a positive sol, the flocculating power
is in the order: [Fe(CN)₆]⁴⁻ > PO4³⁻ > SO4²⁻ > Cl–
The minimum concentration of an electrolyte in millimoles per litre
required to cause precipitation of a sol in two hours is called coagulating
value. The smaller the quantity needed, the higher will be the coagulating
power of an ion.
2. sols are coagulated by effective ions whose charge is opposite to that of sol and the ions of higher charge are much more effective than the ions of lower charge
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.Tails of comets are visible due to:
1. Tyndall effect
2. reflection
3. Brownian motion
4. none of these
.
.
Answer ▽ ✅Verified
The droplets in emulsions are often negatively charged
and can be precipitated by electrolytes. They also show Brownian
movement and Tyndall effect. Emulsions can be broken into constituent
liquids by heating, freezing, centrifuging, etc
and can be precipitated by electrolytes. They also show Brownian
movement and Tyndall effect. Emulsions can be broken into constituent
liquids by heating, freezing, centrifuging, etc
As comets come near to the Sun, tails of dust and ionized gas are developed. Comets contain two tails, a dust tail and a plasma tail. The dust tail looks whitish-yellow as it comprises tiny particles, about the smoke particles size which reflect sunlight. Tail of comets appears as a Tyndall cone because of the scattering of light by the tiny solid particles that are left behind by the comet in its route.
We can define the Tyndall effect as the phenomenon of scattering of particles of light in its path. When a beam of sunlight enters into the dusty window through the window, then its path becomes visible to us. We have to know the effect of scattering of light in colloidal dispersion, while displaying no light in a true solution is known as Tyndall effect. We can use this effect to determine if a mixture is a true solution or a colloid.
Therefore, the option (A) is correct
We can say reflection is a spot in a diffraction pattern.
Therefore, the option (B) is incorrect.
Colloidal particles that are present in a colloidal solution show a vital property called the Brownian movement. We can define Brownian movement as the uninterrupted zigzag movement of the colloidal particles in the dispersion medium present in a colloidal solution. We can say Brownian movement is due to the unequal bombardment of the moving molecules of dispersion medium on colloidal particles. The moving molecules of the dispersion medium strike on colloidal particles from all sides and transfer momentum to them.We must remember that the Brownian movement plays a vital role in imparting stability to a sol. This is because the Brownian movement opposes the gravitational forces that act on colloidal particles and prevent them from getting settled down.
Therefore, the option (C) is incorrect.
Therefore, the option (A) is correct.
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.Bleeding is stoped by the application of ferric chloride. This is because :
1. the blood starts flowing in the opposite direction
2. the blood reacts and a solid is formed which seals the blood vessel
3. the blood is coagulated and the blood vessel are sealed
4. the ferric chloride seals the blood vessel
.
.
Answer ▽ ✅Verified
3. the blood is coagulated and the blood vessel are sealed
Blood: It is a colloidal solution of an albuminoid substance. The
styptic action of alum and ferric chloride solution is due to
coagulation of blood forming a clot which stops further bleeding.
styptic action of alum and ferric chloride solution is due to
coagulation of blood forming a clot which stops further bleeding.
Colloids Around Us
Most of the substances, we come across in our daily life, are colloids. The meals we eat, the clothes we wear, the wooden furniture we use, the houses we live in, the newspapers we read, are largely composed of colloids.
Following are the interesting and noteworthy examples of colloids:
(i) Blue colour of the sky: Dust particles along with water suspended in air
scatter blue light which reaches our eyes and the sky looks blue to us.
(ii) Fog, mist and rain: When a large mass of air containing dust
particles, is cooled below its dewpoint, the moisture from the air
condenses on the surfaces of these particles forming fine droplets.
These droplets being colloidal in nature continue to float in air in
the form of mist or fog. Clouds are aerosols having small droplets
of water suspended in air. On account of condensation in the
upper atmosphere, the colloidal droplets of water grow bigger and
bigger in size, till they come down in the form of rain. Sometimes,
the rainfall occurs when two oppositely charged clouds meet.
It is possible to cause artificial rain by throwing electrified
sand or spraying a sol carrying charge opposite to the one on
clouds from an aeroplane.
(iii) Food articles: Milk, butter, halwa, ice creams, fruit juices, etc., are
all colloids in one form or the other.
(iv) Blood: It is a colloidal solution of an albuminoid substance. The
styptic action of alum and ferric chloride solution is due to
coagulation of blood forming a clot which stops further bleeding.
(v) Soils: Fertile soils are colloidal in nature in which humus acts as
a protective colloid. On account of colloidal nature, soils adsorb
moisture and nourishing materials.
(vi) Formation of delta: River water is a colloidal solution of clay. Sea
water contains a number of electrolytes. When river water meets the
sea water, the electrolytes present in sea water coagulate the colloidal
solution of clay resulting in its deposition with the formation of delta.
(i) Blue colour of the sky: Dust particles along with water suspended in air
scatter blue light which reaches our eyes and the sky looks blue to us.
(ii) Fog, mist and rain: When a large mass of air containing dust
particles, is cooled below its dewpoint, the moisture from the air
condenses on the surfaces of these particles forming fine droplets.
These droplets being colloidal in nature continue to float in air in
the form of mist or fog. Clouds are aerosols having small droplets
of water suspended in air. On account of condensation in the
upper atmosphere, the colloidal droplets of water grow bigger and
bigger in size, till they come down in the form of rain. Sometimes,
the rainfall occurs when two oppositely charged clouds meet.
It is possible to cause artificial rain by throwing electrified
sand or spraying a sol carrying charge opposite to the one on
clouds from an aeroplane.
(iii) Food articles: Milk, butter, halwa, ice creams, fruit juices, etc., are
all colloids in one form or the other.
(iv) Blood: It is a colloidal solution of an albuminoid substance. The
styptic action of alum and ferric chloride solution is due to
coagulation of blood forming a clot which stops further bleeding.
(v) Soils: Fertile soils are colloidal in nature in which humus acts as
a protective colloid. On account of colloidal nature, soils adsorb
moisture and nourishing materials.
(vi) Formation of delta: River water is a colloidal solution of clay. Sea
water contains a number of electrolytes. When river water meets the
sea water, the electrolytes present in sea water coagulate the colloidal
solution of clay resulting in its deposition with the formation of delta.
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.Chemisorption is:
1. multimolecular in nature
2. reversible
3. often highly specific and directional
4. not very specific
.
.Subtopic: Adsorption and Absorption |
Answer ▽ ✅Verified
3. often highly specific and directional
Types of Adsorption
There are mainly two types of adsorption of gases on solids.If accumulation of gas on the surface of a solid occurs on account of
weak van der Waals’ forces, the adsorption is termed as physical
adsorption or physisorption. When the gas molecules or atoms are
held to the solid surface by chemical bonds, the adsorption is termed
chemical adsorption or chemisorption. The chemical bonds may be
covalent or ionic in nature. Chemisorption involves a high energy of
activation and is, therefore, often referred to as activated adsorption.
Sometimes these two processes occur simultaneously and it is not
easy to ascertain the type of adsorption. A physical adsorption at low
temperature may pass into chemisorption as the temperature is
increased. For example, dihydrogen is first adsorbed on nickel by van
der Waals’ forces. Molecules of hydrogen then dissociate to form.
Characteristics of physisorption
(i) Lack of specificity: A given surface of an adsorbent does not show anypreference for a particular gas as the van der Waals’ forces are universal.
(ii) Nature of adsorbate: The amount of gas adsorbed by a solid
depends on the nature of gas. In general, easily liquefiable gases
(i.e., with higher critical temperatures) are readily adsorbed as van
der Waals’ forces are stronger near the critical temperatures. Thus,
1g of activated charcoal adsorbs more sulphur dioxide (critical
temperature 630K), than methane (critical temperature 190K) which
is still more than 4.5 mL of dihydrogen (critical temperature 33K).
(iii) Reversible nature: Physical adsorption of a gas by a solid is
generally reversible. Thus,
Solid + Gas to Gas/Solid + Heat or visa versa.
More of gas is adsorbed when pressure is increased as the
volume of the gas decreases (Le–Chateliers’s principle) and the
gas can be removed by decreasing pressure. Since the adsorption
process is exothermic, the physical adsorption occurs readily at
low temperature and decreases with increasing temperature
(Le-Chatelier’s principle).
(iv) Surface area of adsorbent: The extent of adsorption increases
with the increase of surface area of the adsorbent. Thus, finely
divided metals and porous substances having large surface areas
are good adsorbents.
(v) Enthalpy of adsorption: No doubt, physical adsorption is an
exothermic process but its enthalpy of adsorption is quite low (20–
40 kJ mol-1). This is because the attraction between gas molecules
and solid surface is only due to weak van der Waals’ forces.
Characteristics of chemisorption
(i) High specificity: Chemisorption is highly specific and it will
only occur if there is some possibility of chemical bonding
between adsorbent and adsorbate. For example, oxygen is
adsorbed on metals by virtue of oxide formation and hydrogen
is adsorbed by transition metals due to hydride formation.
(ii) Irreversibility: As chemisorption involves compound formation, it is usually irreversible in nature. Chemisorption is also an
exothermic process but the process is very slow at low
temperatures on account of high energy of activation. Like most
chemical changes, adsorption often increases with rise of
temperature. Physisorption of a gas adsorbed at low temperature
may change into chemisorption at a high temperature. Usually
high pressure is also favourable for chemisorption.
(iii) Surface area: Like physical adsorption, chemisorption also
increases with increase of surface area of the adsorbent.
(iv) Enthalpy of adsorption: Enthalpy of chemisorption is high
(80-240 kJ mol-1) as it involves chemical bond formation.
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.Detergent action of synthetic detergents is due to their:
1. interfacial area
2. high molar mass
3. ionization
4. emulsifying properties
.
.Subtopic: Emulsions/Synthetic Detergents
Answer ▽ ✅Verified
4. emulsifying properties
Synthetic Detergents
Synthetic detergents are cleansing agents which have all the properties of soaps, but which actually do not contain any soap. These can be
used both in soft and hard water as they give foam even in hard water.
Some of the detergents give foam even in ice cold water.
Synthetic detergents are mainly classified into three categories:
(i) Anionic detergents (ii) Cationic detergents and (iii) Non-ionic
detergents
(i) Anionic Detergents: Anionic detergents are sodium salts of
sulphonated long chain alcohols or hydrocarbons. Alkyl
hydrogensulphates formed by treating long chain alcohols with
concentrated sulphuric acid are neutralised with alkali to form
anionic detergents. Similarly alkyl benzene sulphonates are
obtained by neutralising alkyl benzene sulphonic acids with alkali.
In anionic detergents, the anionic part of the molecule is involved
in the cleansing action. Sodium salts of alkylbenzenesulphonates
are an important class of anionic detergents.
They are mostly used for household work. Anionic detergents
are also used in toothpastes.
(ii) Cationic Detergents: Cationic detergents are quarternary
ammonium salts of amines with acetates, chlorides or bromides
as anions.
in the cleansing action. Sodium salts of alkylbenzenesulphonates
are an important class of anionic detergents.
They are mostly used for household work. Anionic detergents
are also used in toothpastes.
(ii) Cationic Detergents: Cationic detergents are quarternary
ammonium salts of amines with acetates, chlorides or bromides
as anions.
Cationic part
possess a long hydrocarbon
chain and a positive charge on
nitrogen atom. Hence, these are
called cationic detergents.
Cetyltrimethylammonium
bromide is a popular cationic
detergent and is used in hair
conditioners.
Cationic detergents have germicidal properties and are expensive,
therefore, these are of limited use.
(iii) Non-ionic Detergents: Non-ionic detergents do not contain any ion in their constitution. One such detergent is formed when stearic acid reacts with polyethyleneglycol.
Liquid dishwashing detergents are non-ionic type. Mechanism of cleansing action of this type of detergents is the same as that of
soaps. These also remove grease and oil by micelle formation.
Main problem that appears in the use of detergents is that if their hydrocarbon chain is highly branched, then bacteria cannot degrade
this easily. Slow degradation of detergents leads to their accumulation.
Effluents containing such detergents reach the rivers, ponds, etc.
These persist in water even after sewage treatment and cause foaming
in rivers, ponds and streams and their water gets polluted.
These days the branching of the hydrocarbon chain is controlled and kept to the minimum. Unbranched chains can be biodegraded
more easily and hence pollution is prevented.
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.Among the electrolytes Na2SO4, CaCl2, Al2(SO4)3 and NH4Cl, the most effective coagulating agent for Sb2S3 sol is :
1. Na2SO4
2. CaCl2
3. Al2(SO4)3
4. NH4Cl
.
.
Answer ▽ ✅Verified
3. Al2(SO4)3
Coagulation or precipitation: The stability of
the lyophobic sols is due to the presence of charge
on colloidal particles. If, somehow, the charge is
removed, the particles will come nearer to each other
to form aggregates (or coagulate) and settle down
under the force of gravity.
The coagulation of the lyophobic sols can be
carried out in the following ways:
(i) By electrophoresis: The colloidal particles move towards oppositely
charged electrodes, get discharged and precipitated.
(ii) By mixing two oppositely charged sols: Oppositely charged sols when
mixed in almost equal proportions, neutralise their charges and get
partially or completely precipitated. Mixing of hydrated ferric oxide (+ve sol) and arsenious sulphide (–ve sol) bring them in the precipitated
forms. This type of coagulation is called mutual coagulation.
(iii) By boiling: When a sol is boiled, the adsorbed layer is disturbed
due to increased collisions with the molecules of dispersion
medium. This reduces the charge on the particles and ultimately
leads to settling down in the form of a precipitate.
(iv) By persistent dialysis: On prolonged dialysis, traces of the
electrolyte present in the sol are removed almost completely and
the colloids become unstable and ultimately coagulate.
(v) By addition of electrolytes: When excess of an electrolyte is added,
the colloidal particles are precipitated. The reason is that colloids
interact with ions carrying charge opposite to that present on
themselves. This causes neutralisation leading to their coagulation.
The ion responsible for neutralisation of charge on the particles is
called the coagulating ion. A negative ion causes the precipitation
of positively charged sol and vice versa.
It has been observed that, generally, the greater the valence of the flocculating ion added, the greater is its power to cause precipitation.
This is known as Hardy-Schulze rule. In the coagulation of a negative
sol, the flocculating power is in the order: Al3+>Ba2+>Na+
Similarly, in the coagulation of a positive sol, the flocculating power
is in the order: [Fe(CN)6]⁴⁻> PO4³⁻> SO4²⁻> Cl–
The minimum concentration of an electrolyte in millimoles per litre
required to cause precipitation of a sol in two hours is called coagulating
value. The smaller the quantity needed, the higher will be the coagulating
power of an ion.
the lyophobic sols is due to the presence of charge
on colloidal particles. If, somehow, the charge is
removed, the particles will come nearer to each other
to form aggregates (or coagulate) and settle down
under the force of gravity.
The process of settling of colloidal particles is called coagulation or precipitation of the sol.
The coagulation of the lyophobic sols can be
carried out in the following ways:
(i) By electrophoresis: The colloidal particles move towards oppositely
charged electrodes, get discharged and precipitated.
(ii) By mixing two oppositely charged sols: Oppositely charged sols when
mixed in almost equal proportions, neutralise their charges and get
partially or completely precipitated. Mixing of hydrated ferric oxide (+ve sol) and arsenious sulphide (–ve sol) bring them in the precipitated
forms. This type of coagulation is called mutual coagulation.
(iii) By boiling: When a sol is boiled, the adsorbed layer is disturbed
due to increased collisions with the molecules of dispersion
medium. This reduces the charge on the particles and ultimately
leads to settling down in the form of a precipitate.
(iv) By persistent dialysis: On prolonged dialysis, traces of the
electrolyte present in the sol are removed almost completely and
the colloids become unstable and ultimately coagulate.
(v) By addition of electrolytes: When excess of an electrolyte is added,
the colloidal particles are precipitated. The reason is that colloids
interact with ions carrying charge opposite to that present on
themselves. This causes neutralisation leading to their coagulation.
The ion responsible for neutralisation of charge on the particles is
called the coagulating ion. A negative ion causes the precipitation
of positively charged sol and vice versa.
It has been observed that, generally, the greater the valence of the flocculating ion added, the greater is its power to cause precipitation.
This is known as Hardy-Schulze rule. In the coagulation of a negative
sol, the flocculating power is in the order: Al3+>Ba2+>Na+
Similarly, in the coagulation of a positive sol, the flocculating power
is in the order: [Fe(CN)6]⁴⁻> PO4³⁻> SO4²⁻> Cl–
The minimum concentration of an electrolyte in millimoles per litre
required to cause precipitation of a sol in two hours is called coagulating
value. The smaller the quantity needed, the higher will be the coagulating
power of an ion.
Coagulation of lyophilic sols
There are two factors which are responsible for the stability of lyophilic
sols. These factors are the charge and solvation of the colloidal particles.
When these two factors are removed, a lyophilic sol can be coagulated.
This is done (i) by adding an electrolyte and (ii) by adding a suitable
solvent. When solvents such as alcohol and acetone are added to
hydrophilic sols, the dehydration of dispersed phase occurs. Under this
condition, a small quantity of electrolyte can bring about coagulation.
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.The arsenious sulphide sol has negative charge. The maximum coagulationg power for precipitating it is of :
1. 0.1 N Zn(NO3)2
2. 0.1 N Na3PO4
3. 0.1 N ZnSO2
4. 0.1 N AlCl3
.
.
Answer ▽ ✅Verified
4. 0.1 N AlCl3
Coagulation or precipitation: The stability of
the lyophobic sols is due to the presence of charge
on colloidal particles. If, somehow, the charge is
removed, the particles will come nearer to each other
to form aggregates (or coagulate) and settle down
under the force of gravity.
The coagulation of the lyophobic sols can be
carried out in the following ways:
(i) By electrophoresis: The colloidal particles move towards oppositely
charged electrodes, get discharged and precipitated.
(ii) By mixing two oppositely charged sols: Oppositely charged sols when
mixed in almost equal proportions, neutralise their charges and get
partially or completely precipitated. Mixing of hydrated ferric oxide (+ve sol) and arsenious sulphide (–ve sol) bring them in the precipitated
forms. This type of coagulation is called mutual coagulation.
(iii) By boiling: When a sol is boiled, the adsorbed layer is disturbed
due to increased collisions with the molecules of dispersion
medium. This reduces the charge on the particles and ultimately
leads to settling down in the form of a precipitate.
(iv) By persistent dialysis: On prolonged dialysis, traces of the
electrolyte present in the sol are removed almost completely and
the colloids become unstable and ultimately coagulate.
(v) By addition of electrolytes: When excess of an electrolyte is added,
the colloidal particles are precipitated. The reason is that colloids
interact with ions carrying charge opposite to that present on
themselves. This causes neutralisation leading to their coagulation.
The ion responsible for neutralisation of charge on the particles is
called the coagulating ion. A negative ion causes the precipitation
of positively charged sol and vice versa.
It has been observed that, generally, the greater the valence of the flocculating ion added, the greater is its power to cause precipitation.
This is known as Hardy-Schulze rule. In the coagulation of a negative
sol, the flocculating power is in the order: Al3+>Ba2+>Na+
Similarly, in the coagulation of a positive sol, the flocculating power
is in the order: [Fe(CN)6]⁴⁻> PO4³⁻> SO4²⁻> Cl–
The minimum concentration of an electrolyte in millimoles per litre
required to cause precipitation of a sol in two hours is called coagulating
value. The smaller the quantity needed, the higher will be the coagulating
power of an ion.
the lyophobic sols is due to the presence of charge
on colloidal particles. If, somehow, the charge is
removed, the particles will come nearer to each other
to form aggregates (or coagulate) and settle down
under the force of gravity.
The process of settling of colloidal particles is called coagulation or precipitation of the sol.
The coagulation of the lyophobic sols can be
carried out in the following ways:
(i) By electrophoresis: The colloidal particles move towards oppositely
charged electrodes, get discharged and precipitated.
(ii) By mixing two oppositely charged sols: Oppositely charged sols when
mixed in almost equal proportions, neutralise their charges and get
partially or completely precipitated. Mixing of hydrated ferric oxide (+ve sol) and arsenious sulphide (–ve sol) bring them in the precipitated
forms. This type of coagulation is called mutual coagulation.
(iii) By boiling: When a sol is boiled, the adsorbed layer is disturbed
due to increased collisions with the molecules of dispersion
medium. This reduces the charge on the particles and ultimately
leads to settling down in the form of a precipitate.
(iv) By persistent dialysis: On prolonged dialysis, traces of the
electrolyte present in the sol are removed almost completely and
the colloids become unstable and ultimately coagulate.
(v) By addition of electrolytes: When excess of an electrolyte is added,
the colloidal particles are precipitated. The reason is that colloids
interact with ions carrying charge opposite to that present on
themselves. This causes neutralisation leading to their coagulation.
The ion responsible for neutralisation of charge on the particles is
called the coagulating ion. A negative ion causes the precipitation
of positively charged sol and vice versa.
It has been observed that, generally, the greater the valence of the flocculating ion added, the greater is its power to cause precipitation.
This is known as Hardy-Schulze rule. In the coagulation of a negative
sol, the flocculating power is in the order: Al3+>Ba2+>Na+
Similarly, in the coagulation of a positive sol, the flocculating power
is in the order: [Fe(CN)6]⁴⁻> PO4³⁻> SO4²⁻> Cl–
The minimum concentration of an electrolyte in millimoles per litre
required to cause precipitation of a sol in two hours is called coagulating
value. The smaller the quantity needed, the higher will be the coagulating
power of an ion.
Coagulation of lyophilic sols
There are two factors which are responsible for the stability of lyophilic
sols. These factors are the charge and solvation of the colloidal particles.
When these two factors are removed, a lyophilic sol can be coagulated.
This is done (i) by adding an electrolyte and (ii) by adding a suitable
solvent. When solvents such as alcohol and acetone are added to
hydrophilic sols, the dehydration of dispersed phase occurs. Under this
condition, a small quantity of electrolyte can bring about coagulation.
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.An emulsifier is a substance which:
1. Homogenesis the emulsion
2. stabliizes the emulsion
3. retards the dispersion of liquid in liquid
4. coagulates the emulsion
.
.
Answer ▽ ✅Verified
2. stabliizes the emulsion
Colloidal solutions are intermediate between true solutions and suspensions.
The size of the colloidal particles range from 1 to 1000 nm. A colloidal system consists
of two phases - the dispersed phase and the dispersion medium. Colloidal systems
are classified in three ways depending upon (i) physical states of the dispersed phase
and dispersion medium (ii) nature of interaction between the dispersed phase and
dispersion medium and (iii) nature of particles of dispersed phase. The colloidal
systems show interesting optical, mechanical and electrical properties. The process
of changing the colloidal particles in a sol into the insoluble precipitate by addition
of some suitable electrolytes is known as coagulation. Emulsions are colloidal systems
in which both dispersed phase and dispersion medium are liquids. These can be of:
(i) oil in water type and (ii) water in oil type. The process of making emulsion is
known as emulsification. To stabilise an emulsion, an emulsifying agent or emulsifier
is added. Soaps and detergents are most frequently used as emulsifiers. Colloids find
several applications in industry as well as in daily life.
The size of the colloidal particles range from 1 to 1000 nm. A colloidal system consists
of two phases - the dispersed phase and the dispersion medium. Colloidal systems
are classified in three ways depending upon (i) physical states of the dispersed phase
and dispersion medium (ii) nature of interaction between the dispersed phase and
dispersion medium and (iii) nature of particles of dispersed phase. The colloidal
systems show interesting optical, mechanical and electrical properties. The process
of changing the colloidal particles in a sol into the insoluble precipitate by addition
of some suitable electrolytes is known as coagulation. Emulsions are colloidal systems
in which both dispersed phase and dispersion medium are liquids. These can be of:
(i) oil in water type and (ii) water in oil type. The process of making emulsion is
known as emulsification. To stabilise an emulsion, an emulsifying agent or emulsifier
is added. Soaps and detergents are most frequently used as emulsifiers. Colloids find
several applications in industry as well as in daily life.
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.Flocculation value is expressed in terms of:
1. Millimole per litre.
2. Mole per litre.
3. Gram per litre.
4. Mole per millilitre.
.
.
Answer ▽ ✅Verified
Coagulation or precipitation: The stability of
the lyophobic sols is due to the presence of charge
on colloidal particles. If, somehow, the charge is
removed, the particles will come nearer to each other
to form aggregates (or coagulate) and settle down
under the force of gravity.
The coagulation of the lyophobic sols can be
carried out in the following ways:
(i) By electrophoresis: The colloidal particles move towards oppositely
charged electrodes, get discharged and precipitated.
(ii) By mixing two oppositely charged sols: Oppositely charged sols when
mixed in almost equal proportions, neutralise their charges and get
partially or completely precipitated. Mixing of hydrated ferric oxide (+ve sol) and arsenious sulphide (–ve sol) bring them in the precipitated
forms. This type of coagulation is called mutual coagulation.
(iii) By boiling: When a sol is boiled, the adsorbed layer is disturbed
due to increased collisions with the molecules of dispersion
medium. This reduces the charge on the particles and ultimately
leads to settling down in the form of a precipitate.
(iv) By persistent dialysis: On prolonged dialysis, traces of the
electrolyte present in the sol are removed almost completely and
the colloids become unstable and ultimately coagulate.
(v) By addition of electrolytes: When excess of an electrolyte is added,
the colloidal particles are precipitated. The reason is that colloids
interact with ions carrying charge opposite to that present on
themselves. This causes neutralisation leading to their coagulation.
The ion responsible for neutralisation of charge on the particles is
called the coagulating ion. A negative ion causes the precipitation
of positively charged sol and vice versa.
It has been observed that, generally, the greater the valence of the flocculating ion added, the greater is its power to cause precipitation.
This is known as Hardy-Schulze rule. In the coagulation of a negative
sol, the flocculating power is in the order: Al3+>Ba2+>Na+
Similarly, in the coagulation of a positive sol, the flocculating power
is in the order: [Fe(CN)6]⁴⁻> PO4³⁻> SO4²⁻> Cl–
The minimum concentration of an electrolyte in millimoles per litre
required to cause precipitation of a sol in two hours is called coagulating
value. The smaller the quantity needed, the higher will be the coagulating
power of an ion.
the lyophobic sols is due to the presence of charge
on colloidal particles. If, somehow, the charge is
removed, the particles will come nearer to each other
to form aggregates (or coagulate) and settle down
under the force of gravity.
The process of settling of colloidal particles is called coagulation or precipitation of the sol.
The coagulation of the lyophobic sols can be
carried out in the following ways:
(i) By electrophoresis: The colloidal particles move towards oppositely
charged electrodes, get discharged and precipitated.
(ii) By mixing two oppositely charged sols: Oppositely charged sols when
mixed in almost equal proportions, neutralise their charges and get
partially or completely precipitated. Mixing of hydrated ferric oxide (+ve sol) and arsenious sulphide (–ve sol) bring them in the precipitated
forms. This type of coagulation is called mutual coagulation.
(iii) By boiling: When a sol is boiled, the adsorbed layer is disturbed
due to increased collisions with the molecules of dispersion
medium. This reduces the charge on the particles and ultimately
leads to settling down in the form of a precipitate.
(iv) By persistent dialysis: On prolonged dialysis, traces of the
electrolyte present in the sol are removed almost completely and
the colloids become unstable and ultimately coagulate.
(v) By addition of electrolytes: When excess of an electrolyte is added,
the colloidal particles are precipitated. The reason is that colloids
interact with ions carrying charge opposite to that present on
themselves. This causes neutralisation leading to their coagulation.
The ion responsible for neutralisation of charge on the particles is
called the coagulating ion. A negative ion causes the precipitation
of positively charged sol and vice versa.
It has been observed that, generally, the greater the valence of the flocculating ion added, the greater is its power to cause precipitation.
This is known as Hardy-Schulze rule. In the coagulation of a negative
sol, the flocculating power is in the order: Al3+>Ba2+>Na+
Similarly, in the coagulation of a positive sol, the flocculating power
is in the order: [Fe(CN)6]⁴⁻> PO4³⁻> SO4²⁻> Cl–
The minimum concentration of an electrolyte in millimoles per litre
required to cause precipitation of a sol in two hours is called coagulating
value. The smaller the quantity needed, the higher will be the coagulating
power of an ion.
Coagulation of lyophilic sols
There are two factors which are responsible for the stability of lyophilic
sols. These factors are the charge and solvation of the colloidal particles.
When these two factors are removed, a lyophilic sol can be coagulated.
This is done (i) by adding an electrolyte and (ii) by adding a suitable
solvent. When solvents such as alcohol and acetone are added to
hydrophilic sols, the dehydration of dispersed phase occurs. Under this
condition, a small quantity of electrolyte can bring about coagulation.
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.KClO3 on heating decomposes into KCl and O2. If some MnO2 is added the reaction goes much faster because:
1. MnO2 decomposes to give oxygen.
2. MnO2 provides heat by reacting.
3. Better contact is provided by MnO2
4. MnO2 acts as a catalyst.
.
.
Answer ▽ ✅Verified
4. MnO2 acts as a catalyst.
In laboratory, dioxygen is prepared by heating
KClO3 in presence of MnO2. It forms a number of oxides with metals.
KClO3 in presence of MnO2. It forms a number of oxides with metals.
Additional information
Potassium permanganate KMnO4
Potassium permanganate is prepared by fusion of MnO2 with an alkali
metal hydroxide and an oxidising agent like KNO3. This produces the
dark green K2MnO4 which disproportionates in a neutral or acidic
solution to give permanganate.
Commercially it is prepared by the alkaline oxidative fusion of MnO2
followed by the electrolytic oxidation of manganate (Vl).
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.The blue colour of the water of the sea is due to :
1. refraction of the blue light by the imputities in sea water
2. reflection of blue light by sea water
3. scattering of blue light by sol particles
4. absorption of other colours except the blue colour by water molecules
.
.
Answer ▽ ✅Verified
3. scattering of blue light by sol particles
Properties of Colloidal Solutions
.Various properties exhibited by the colloidal solutions are described below:(i) Colligative properties: Colloidal particles being bigger aggregates,
the number of particles in a colloidal solution is comparatively
small as compared to a true solution. Hence, the values of colligative
properties (osmotic pressure, lowering in vapour pressure,
depression in freezing point and elevation in boiling point) are of
small order as compared to values shown by true solutions at
same concentrations.
(ii) Tyndall effect: If a homogeneous solution placed
in dark is observed in the direction of light, it
appears clear and, if it is observed from a direction
at right angles to the direction of light beam, it
appears perfectly dark. Colloidal solutions viewed
in the same way may also appear reasonably clear
or translucent by the transmitted light but they
show a mild to strong opalescence, when viewed
at right angles to the passage of light, i.e., the
path of the beam is illuminated by a bluish light.
This effect was first observed by Faraday and later
studied in detail by Tyndall and is termed as
Tyndall effect. The bright cone of the light is
called Tyndall cone (Fig. 5.11). The Tyndall effect
is due to the fact that colloidal particles scatter light in all
directions in space. This scattering of light illuminates the
path of beam in the colloidal dispersion.
Tyndall effect can be observed during the projection
of picture in the cinema hall due to scattering of light by dust and
smoke particles present there. Tyndall effect is observed only when the
following two conditions are satisfied.
(i) The diameter of the dispersed particles is not much smaller than
the wavelength of the light used; and
(ii) The refractive indices of the dispersed phase and the dispersion
medium differ greatly in magnitude.
Tyndall effect is used to distinguish between a colloidal and true
solution. Zsigmondy, in 1903, used Tyndall effect to set up an
apparatus known as ultramicroscope. An intense beam of light is
focussed on the colloidal solution contained in a glass vessel. The
focus of the light is then observed with a microscope at right angles to
the beam. Individual colloidal particles appear as bright stars against
a dark background. Ultramicroscope does not render the actual colloidal
particles visible but only observe the light scattered by them. Thus,
ultramicroscope does not provide any information about the size and
shape of colloidal particles.
(iii) Colour: The colour of colloidal solution depends on the wavelength
of light scattered by the dispersed particles. The wavelength of light
further depends on the size and nature of the particles. The colour of colloidal solution also changes with the manner in which the
observer receives the light. For example, a mixture of milk and water
appears blue when viewed by the reflected light and red when viewed
by the transmitted light. Finest gold sol is red in colour; as the size
of particles increases, it appears purple, then blue and finally golden.
(iv) Brownian movement: When colloidal solutions are viewed under
a powerful ultramicroscope, the colloidal particles appear to be in
a state of continuous zig-zag motion all over the field of view. This
motion was first observed by the British botanist, Robert Brown,
and is known as Brownian movement (Fig. 5.12). This motion
is independent of the nature of the colloid but depends on
the size of the particles and viscosity of the solution. Smaller
the size and lesser the viscosity, faster is the motion.
The Brownian movement has been explained to be due
to the unbalanced bombardment of the particles by the
molecules of the dispersion medium. The Brownian movement
has a stirring effect which does not permit the particles to
settle and thus, is responsible for the stability of sols.
(v) Charge on colloidal particles: Colloidal particles always carry
an electric charge. The nature of this charge is the same on all
the particles in a given colloidal solution and may be either
positive or negative.
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.Lyophobic colloids are:
1. reversible colloids
2. irreversible colloids
3. protective colloids
4. gum, proteins
.
.
Answer ▽ ✅Verified
2. irreversible colloids
Depending upon the nature of interaction between the dispersed phase
and the dispersion medium, colloidal sols are divided into two categories,
namely, lyophilic (solvent attracting) and lyophobic (solvent repelling).
If water is the dispersion medium, the terms used are hydrophilic and
hydrophobic.
(i) Lyophilic colloids: The word ‘lyophilic’ means liquid-loving. Colloidal
sols directly formed by mixing substances like gum, gelatine, starch,
rubber, etc., with a suitable liquid (the dispersion medium) are
called lyophilic sols. An important characteristic of these sols is
that if the dispersion medium is separated from the dispersed
phase (say by evaporation), the sol can be reconstituted by simply
remixing with the dispersion medium. That is why these sols are
also called reversible sols. Furthermore, these sols are quite stable
and cannot be easily coagulated as discussed later.
(ii) Lyophobic colloids: The word ‘lyophobic’ means liquid-hating.
Substances like metals, their sulphides, etc., when simply mixed
with the dispersion medium do not form the colloidal sol. Their
colloidal sols can be prepared only by special methods (as discussed
later). Such sols are called lyophobic sols. These sols are readily
precipitated (or coagulated) on the addition of small amounts of
electrolytes, by heating or by shaking and hence, are not stable.
Further, once precipitated, they do not give back the colloidal sol
by simple addition of the dispersion medium. Hence, these sols
are also called irreversible sols. Lyophobic sols need stabilising
agents for their preservation.
and the dispersion medium, colloidal sols are divided into two categories,
namely, lyophilic (solvent attracting) and lyophobic (solvent repelling).
If water is the dispersion medium, the terms used are hydrophilic and
hydrophobic.
(i) Lyophilic colloids: The word ‘lyophilic’ means liquid-loving. Colloidal
sols directly formed by mixing substances like gum, gelatine, starch,
rubber, etc., with a suitable liquid (the dispersion medium) are
called lyophilic sols. An important characteristic of these sols is
that if the dispersion medium is separated from the dispersed
phase (say by evaporation), the sol can be reconstituted by simply
remixing with the dispersion medium. That is why these sols are
also called reversible sols. Furthermore, these sols are quite stable
and cannot be easily coagulated as discussed later.
(ii) Lyophobic colloids: The word ‘lyophobic’ means liquid-hating.
Substances like metals, their sulphides, etc., when simply mixed
with the dispersion medium do not form the colloidal sol. Their
colloidal sols can be prepared only by special methods (as discussed
later). Such sols are called lyophobic sols. These sols are readily
precipitated (or coagulated) on the addition of small amounts of
electrolytes, by heating or by shaking and hence, are not stable.
Further, once precipitated, they do not give back the colloidal sol
by simple addition of the dispersion medium. Hence, these sols
are also called irreversible sols. Lyophobic sols need stabilising
agents for their preservation.
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.Which one has the highest coagulation power?
(1) K+
(2) Ca++
(3) Al+++
(4) Sn4+
.
.
Answer ▽ ✅Verified
(4) Sn4+
⬆️Prev____@organised notes_____Next⬇️
.According to Freundlich adsorption isotherm, which of the following is correct:-
(1)
(2)
(3)
(4) All are correct for different ranges of pressure
.
.
Answer ▽ ✅Verified
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