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iiThe conicalround bottomed flat bottomed flask is connected to a long glass tube called fractionating column
The purpose of the fractionating column is to offer areas of condensation for the less volatile pure mixture
The fractionating column is packed with glass beadsbroken glass porcelain shelves to increase the surface area of condensation of the less volatile pure mixture
iiiWhen the vapors rise they condense on the glass beadsbroken glass porcelain shelves which become hot
When the temperature of the glass beadsbroken glassporcelainshelves is beyond the boiling point of the less volatile pure substance the pure substance rise and condensation take place on the glass beadsbroken glassporcelainshelves at a higher level on the fractionating column
The less volatile pure substance tricklesdrips back down the fractionating column or back into the conicalround bottomed flat bottomed flask to be heated again eg
If the temperature on glass beadsbroken glassporcelainshelves is beyond 78oC the more volatile pure ethanol rise to condense on the glass beadsbroken glass porcelainshelves higher in the fractionating column
Water condenses and then driptrickle to the glass beadsbroken glass porcelain shelves lower in the fractionating column because it is less volatile
iv The fractionating column is connected to a Liebig condenser The Liebig condenser has a cold water inlet and outlet circulation
The more volatile mixture that reach the top of the fractionating column is condenses by the Liebig condenser into a receiver It is collected as the first fraction
vAt the top of the fractionating column a thermometer is placed to notemonitor the temperature of the boiling mixtures
Pure substances have constantfixed boiling point When one mixture is completely separated the thermometer reading rises
Eg the thermometer reading remains at78oC when ethanol is being separated When no more ethanol is being separated the mercuryalcohol level in the thermometer rises
viThe second subsequent fractions are collected in the receiver after noting a rise the mercuryalcohol level in the thermometer
Eg the thermometer reading rises to 100oC when water is being separated It is passed through the Liebig condenser with the cold water inlet and outlet circulation It is collected different receiver as the secondsubsequent fraction
viiEach fraction collected should be confirmed from known physicalchemical propertiescharacteristic
Example
Ethanol
Ethanol is a colourless liquid that has a characteristic smell When it is put in a watch glass then ignited it catches fire and burn with a blue flame
Water
Water is a colourless liquid that has no smellodour When it is put in a watch glass then ignited it does not catch fire
Set up of apparatus
Industrial application of Fractional distillation
On a large scalefractional distillation is used
iIn fractional distillation of crude oil in an oil refinery
Crude oil is a mixture of many fractions When heated in a furnace the different fractions separate out according to their boiling point In Kenyafractional distillation takes place at Changamwe in Mombasa
iiIn fractional distillation of air
Air contain a mixture of three main useful gases which are condensed by cooling to very low temperature 200oC to form a liquid The liquid is then heated Nitrogen is the most volatile 196 oC and thus comes out as the first fraction Argon at 186 oC is the second fraction Oxygen at 183 oC is the last fraction The three gases are very useful industrial gases
fSeparation of immiscibles Using a separating funnel
Two or more liquids that form layers on mixing are immiscible Immiscible mixture arrange themselves according to their densities
ie The denser liquid sink to the bottom The less dense liquid floats on the denser one Immicible mixtures can be separated from each other by using a separating funnel
Experiment To separate an immiscible mixture of paraffin and water
Procedure
Place about 100cm3 of water into a 250cm3 beaker Add about 100cm3 of paraffin into the beaker Stir
Transfer the mixture into a separating funnel Allow to settle for about one minute Open the tap run out the lower layer out slowly into a clean beaker Close the tap when the upper layer is very close to the tap
Run out the intermediate small amount of the mixture near the tap into a beaker Discard it
Run out the remaining upper layer into a fresh beaker
Place a portion of upper and lower layer into a watch glass separately after separating each Ignite
Observation
Water and paraffin are both colourless liquids
Two layers are formed on mixing
Colourless odorless liquid collected first It does not catch fire
A colourless liquid with characteristic smell collected latersecond It catches fire and burn with a yellow smoky flame
Explanation
Water and paraffin are immiscible Water is denser than paraffin When put in a separating funnel paraffin float on water On opening the tap water runs out A mixture of water and paraffin at the junction of the two is discarded It is not pure
Set up of apparatus
gSublimationdeposition
Some solids on heating do not melt to a liquid but change directly to a gas The process by which a solid changes to a gas is called sublimation The gas cools back and changes directly to a solid The process by which a gas changes to a solid is called deposition Sublimation and deposition therefore are the same but opposite processes
Sublimation Deposition
Some common substances that undergo sublimation deposition include
iIodine iiCarbonIVoxide iiiCamphor iv ammonium chloride vIronIIIchloride viAluminumIIIchloride
vii benzoic acid
If a mixture has any of the above as a component then on heating it will change to a gas and be deposited away from the source of heating
Procedure
Place about one spatula full of ammonium chloride crystals into a clean dry 100cm3 beaker Add equal amount of sodium chloride crystals into the beaker Swirl to mix
Place the beaker on a tripod stand
Put about 100cm3 of water into another beaker Place carefully the beaker containing water on top of the beaker containing the solid mixture Lightignite a burner and heat the solid
Set up of apparatus
Observation
iWith ammonium chloridecommon salt mixture
White fumes produced
White sublimate deposited
Colourless residue left
iiWith Iodinecommon salt mixture
Purple fumes produced
Dark grey sublimate deposited
Colourless residue left
Explanation
iOn heating a mixture of ammonium chloride and common salt a white fume of ammonium chloride is produced The white fumes solidify as white sublimate on the cooler parts Common salt remains as residue
Chemical equation
Ammonium chloride solid Ammonium chloride gas
NH4Cls NH4Clg
iiOn heating a mixture of Iodine and common salt a purple fume of Iodine vapour is produced The purple fumes solidify as dark grey sublimate on the cooler parts Common salt remains as residue
Chemical equation
Iodine solid Iodine gas
I2s I2 g
hChromatography
Chromatography is a method of separating components of a solution mixture by passing it through a medium where the different components move at different rates The medium through which the solution mixture is passed is called absorbent material
Paper chromatography is a method of separating colored dyes by using paper as the absorbent material
Since dyes are insolubledo not dissolve in water ethanol and propanone are used as suitable solvents for dissolving the dye
Practically a simple paper chromatography involve placing a dyematerial on the absorbent material adding slowly a suitable soluble solvent on the dyematerial using a dropper the solvent spread out on the absorbent material carrying the soluble dye away from the origin
The spot on which the dye is initiallyoriginally placed is called baseline The farthest point the solvent spread is called solvent front
The farthest a dye can be spread by the solvent depend on
i Density of the dyethe denser the dye the less it spread from the basely ne by the solvent
ii Stickiness of the dyesome dyes sticks on the absorbent material more than other thus do not spread far from baseline
Experiment To investigate the colors in ink
Procedure
Method 1
Place a filter paper on an empty beaker Put a drop of blackblue ink in the centre of the filter paper Wait for about one minute for the ink drop to spread Using a clean teat pipettedropper add one drop of ethanolpropanone Wait for about one minute for the ink drop to spread further Add about twenty other drops of ethanol waiting for about one minute before each addition Allow the filter paper to dry
Experiment To investigate the colors in ink
Procedure
Method 2
Cut an 8 centimeter thin strip of a filter paper At about 3cm on the strip place a drop of ink Place the filter paper in a 10cm length boiling tube containing 5cm3 of ethanol Ensure the cut strip of the filter paper just dips into the ethanol towards the ink mark Cover the boiling tube Wait for about twenty minutes Remove the boiling tube and allow the filter paper to dry
Set up of apparatus
Method 1
Set up of apparatus
Method 2
Explanation
When a drop of ink is placed on an absorbent material it sticks On adding an eluting solvent it dissolves the dye spread out with it The denser and sticky pure dye move least The least densesticky pure dye move farthest A pure dye will produce the same chromatogramspot if the same eluting solvent is used on the same absorbent material Comparing the distance moved by a pure dye with a mixture the coloured dyes in a mixture can be deduced as below
Example 1

iiThe conicalround bottomed flat bottomed flask is connected to a long glass tube called fractionating column

The purpose of the fractionating column is to offer areas of condensation for the less volatile pure mixture

The fractionating column is packed with glass beadsbroken glass porcelain shelves to increase the surface area of condensation of the less volatile pure mixture

iiiWhen the vapors rise they condense on the glass beadsbroken glass porcelain shelves which become hot

When the temperature of the glass beadsbroken glassporcelainshelves is beyond the boiling point of the less volatile pure substance the pure substance rise and condensation take place on the glass beadsbroken glassporcelainshelves at a higher level on the fractionating column

The less volatile pure substance tricklesdrips back down the fractionating column or back into the conicalround bottomed flat bottomed flask to be heated again eg

If the temperature on glass beadsbroken glassporcelainshelves is beyond 78oC the more volatile pure ethanol rise to condense on the glass beadsbroken glass porcelainshelves higher in the fractionating column

Water condenses and then driptrickle to the glass beadsbroken glass porcelain shelves lower in the fractionating column because it is less volatile

iv The fractionating column is connected to a Liebig condenser The Liebig condenser has a cold water inlet and outlet circulation

The more volatile mixture that reach the top of the fractionating column is condenses by the Liebig condenser into a receiver It is collected as the first fraction

vAt the top of the fractionating column a thermometer is placed to notemonitor the temperature of the boiling mixtures

Pure substances have constantfixed boiling point When one mixture is completely separated the thermometer reading rises

Eg the thermometer reading remains at78oC when ethanol is being separated When no more ethanol is being separated the mercuryalcohol level in the thermometer rises

viThe second subsequent fractions are collected in the receiver after noting a rise the mercuryalcohol level in the thermometer

Eg the thermometer reading rises to 100oC when water is being separated It is passed through the Liebig condenser with the cold water inlet and outlet circulation It is collected different receiver as the secondsubsequent fraction

viiEach fraction collected should be confirmed from known physicalchemical propertiescharacteristic

Example

Ethanol

Ethanol is a colourless liquid that has a characteristic smell When it is put in a watch glass then ignited it catches fire and burn with a blue flame

Water

Water is a colourless liquid that has no smellodour When it is put in a watch glass then ignited it does not catch fire

Set up of apparatus

Industrial application of Fractional distillation

On a large scalefractional distillation is used

iIn fractional distillation of crude oil in an oil refinery

Crude oil is a mixture of many fractions When heated in a furnace the different fractions separate out according to their boiling point In Kenyafractional distillation takes place at Changamwe in Mombasa

iiIn fractional distillation of air

Air contain a mixture of three main useful gases which are condensed by cooling to very low temperature 200oC to form a liquid The liquid is then heated Nitrogen is the most volatile 196 oC and thus comes out as the first fraction Argon at 186 oC is the second fraction Oxygen at 183 oC is the last fraction The three gases are very useful industrial gases

fSeparation of immiscibles Using a separating funnel

Two or more liquids that form layers on mixing are immiscible Immiscible mixture arrange themselves according to their densities

ie The denser liquid sink to the bottom The less dense liquid floats on the denser one Immicible mixtures can be separated from each other by using a separating funnel

Experiment To separate an immiscible mixture of paraffin and water

Procedure

Place about 100cm3 of water into a 250cm3 beaker Add about 100cm3 of paraffin into the beaker Stir

Transfer the mixture into a separating funnel Allow to settle for about one minute Open the tap run out the lower layer out slowly into a clean beaker Close the tap when the upper layer is very close to the tap

Run out the intermediate small amount of the mixture near the tap into a beaker Discard it

Run out the remaining upper layer into a fresh beaker

Place a portion of upper and lower layer into a watch glass separately after separating each Ignite

Observation

Water and paraffin are both colourless liquids

Two layers are formed on mixing

Colourless odorless liquid collected first It does not catch fire

A colourless liquid with characteristic smell collected latersecond It catches fire and burn with a yellow smoky flame

Explanation

Water and paraffin are immiscible Water is denser than paraffin When put in a separating funnel paraffin float on water On opening the tap water runs out A mixture of water and paraffin at the junction of the two is discarded It is not pure

Set up of apparatus

gSublimationdeposition

Some solids on heating do not melt to a liquid but change directly to a gas The process by which a solid changes to a gas is called sublimation The gas cools back and changes directly to a solid The process by which a gas changes to a solid is called deposition Sublimation and deposition therefore are the same but opposite processes

Sublimation Deposition

Some common substances that undergo sublimation deposition include

iIodine iiCarbonIVoxide iiiCamphor iv ammonium chloride vIronIIIchloride viAluminumIIIchloride

vii benzoic acid

If a mixture has any of the above as a component then on heating it will change to a gas and be deposited away from the source of heating

Procedure

Place about one spatula full of ammonium chloride crystals into a clean dry 100cm3 beaker Add equal amount of sodium chloride crystals into the beaker Swirl to mix

Place the beaker on a tripod stand

Put about 100cm3 of water into another beaker Place carefully the beaker containing water on top of the beaker containing the solid mixture Lightignite a burner and heat the solid

Set up of apparatus

Observation

iWith ammonium chloridecommon salt mixture

White fumes produced

White sublimate deposited

Colourless residue left

iiWith Iodinecommon salt mixture

Purple fumes produced

Dark grey sublimate deposited

Colourless residue left

Explanation

iOn heating a mixture of ammonium chloride and common salt a white fume of ammonium chloride is produced The white fumes solidify as white sublimate on the cooler parts Common salt remains as residue

Chemical equation

Ammonium chloride solid Ammonium chloride gas

NH4Cls NH4Clg

iiOn heating a mixture of Iodine and common salt a purple fume of Iodine vapour is produced The purple fumes solidify as dark grey sublimate on the cooler parts Common salt remains as residue

Chemical equation

Iodine solid Iodine gas

I2s I2 g

hChromatography

Chromatography is a method of separating components of a solution mixture by passing it through a medium where the different components move at different rates The medium through which the solution mixture is passed is called absorbent material

Paper chromatography is a method of separating colored dyes by using paper as the absorbent material

Since dyes are insolubledo not dissolve in water ethanol and propanone are used as suitable solvents for dissolving the dye

Practically a simple paper chromatography involve placing a dyematerial on the absorbent material adding slowly a suitable soluble solvent on the dyematerial using a dropper the solvent spread out on the absorbent material carrying the soluble dye away from the origin

The spot on which the dye is initiallyoriginally placed is called baseline The farthest point the solvent spread is called solvent front

The farthest a dye can be spread by the solvent depend on

i Density of the dyethe denser the dye the less it spread from the basely ne by the solvent

ii Stickiness of the dyesome dyes sticks on the absorbent material more than other thus do not spread far from baseline

Experiment To investigate the colors in ink

Procedure

Method 1

Place a filter paper on an empty beaker Put a drop of blackblue ink in the centre of the filter paper Wait for about one minute for the ink drop to spread Using a clean teat pipettedropper add one drop of ethanolpropanone Wait for about one minute for the ink drop to spread further Add about twenty other drops of ethanol waiting for about one minute before each addition Allow the filter paper to dry

Experiment To investigate the colors in ink

Procedure

Method 2

Cut an 8 centimeter thin strip of a filter paper At about 3cm on the strip place a drop of ink Place the filter paper in a 10cm length boiling tube containing 5cm3 of ethanol Ensure the cut strip of the filter paper just dips into the ethanol towards the ink mark Cover the boiling tube Wait for about twenty minutes Remove the boiling tube and allow the filter paper to dry

Set up of apparatus

Method 1

Set up of apparatus

Method 2

Explanation

When a drop of ink is placed on an absorbent material it sticks On adding an eluting solvent it dissolves the dye spread out with it The denser and sticky pure dye move least The least densesticky pure dye move farthest A pure dye will produce the same chromatogramspot if the same eluting solvent is used on the same absorbent material Comparing the distance moved by a pure dye with a mixture the coloured dyes in a mixture can be deduced as below

Example 1