Experimental Techniques
Contents:
Learning Objectives ................................................................................................................... 2
1. Common Measuring Instruments ........................................................................................... 3
1.1 Measuring Time ........................................................................................................... 3
1.2 Measuring Temperature ............................................................................................... 3
1.3 Measuring Mass ........................................................................................................... 3
1.4 Measuring Volume ....................................................................................................... 4
2. Mixtures & Pure Substances .................................................................................................. 5
2.1 Pure Substances ............................................................................................................ 5
2.2 Mixtures ....................................................................................................................... 5
2.3 Purification ................................................................................................................... 5
3. Methods of Purification/Separation ....................................................................................... 6
3.1 Filtration ....................................................................................................................... 6
3.2 Crystallisation............................................................................................................... 7
3.3 Use of Separating Funnel ............................................................................................. 9
3.4 Sublimation ................................................................................................................ 10
3.5 Simple Distillation...................................................................................................... 11
3.6 Fractional Distillation ................................................................................................. 13
3.7 Paper Chromatography ............................................................................................... 15
4. Criteria of Purity................................................................................................................... 17
4.1 Importance of Purity................................................................................................... 17
4.2 Test for Purity............................................................................................................. 17
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Learning Objectives
At the end of this unit, you should be able to:
1. Name appropriate apparatus for the measurement of time, temperature, mass and volume.
2. Describe the methods of purification by:
(i) Filtration
(ii) Crystallisation
(iii) The use of a suitable solvent
(iv) Evaporation
(v) The use of separating funnel
(vi) Sublimation
(vii) Simple distillation
(viii) Fractional distillation
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}often used together
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3. Describe paper chromatography and interpret chromatograms.
4. Describe how chromatography techniques can be applied to colourless substances
(knowledge of the composition of particular locating agents is not required).
5. Suggest suitable purification techniques, given information about the substances.
6. Design arrangements of apparatus, given information about the substances involved.
7. Explain the importance of purity in substances in everyday life, example in foodstuffs and
drugs.
8. Identify substances and test their purity by melting point and boiling point determination,
and by paper chromatography.
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1. Common Measuring Instruments
1.1 Measuring _________
Name: _____________
Units: _____________
1.2 Measuring ________________
Name: _________________
Units: _________
 This is a _________________________________.
 Electronic thermometers are increasingly being used nowadays, especially in clinics and
hospitals.
1.3 Measuring ___________
(i) Name: ___________________________
(ii) Name: __________________________
Units: ___________
Units: ____________
 The ________ of a substance is a measure of the amount of ____________ contained in it.
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1.4 Measuring ____________
 Units for the following five apparatus: _______________.
(i) Name: __________
(approximate measurement)
(iv) Name: _____________
(very accurate)
(iii) Name: ____________
(very accurate)
meniscus
(ii) Name: ____________________
(more accurate)
 The beaker, measuring cylinder, burette and pipette are usually used for measuring the
________________ of _____________.
 The pipette measures a __________________ volume of liquid when it is filled to a mark.
(iv) Name: ___________________
 Syringes of different sizes can be used to measure the _______________ of ___________
or ___________.
 Small plastic syringes are used to measure small volumes of liquids. Example: doctors use
it to give a patient an injection.
Larger ones are used to measure volumes of gases.
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2. Mixtures & Pure Substances
2.1 Pure Substances
 A _________ substance is a ___________ substance ______________ with anything else.
Example: sugar crystals.
 It has ______________ properties, such as a __________ melting point and boiling point.
Example: pure water melts at 0oC and boils at 100oC.
2.2 Mixtures
 A ______________ contains __________________ substances.
Examples: ________________ (________________________),
_______ (____________________________________________________),
 It ______________ have definite properties. It _____________ have fixed melting and
boiling points.
It melts and boils over ______________ of several degrees of temperature.
Examples:
Coconut oil used for cooking starts melting at 14oC and completes melting at 22oC.
Petrol fuel for motorcars has a boiling point range of 35oC to 75oC.
2.3 Purification
 Mixtures can easily be separated into pure substances. The process is called
______________________. This is done by physical methods.
 No chemical reactions are needed. Several of these methods will be discussed in the next
Section.
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3. Methods of Purification/Separation
3.1 Filtration
Purpose
 Filtration is a technique used to separate a __________ from a ___________.
Example: sand from water.
Procedure & Setup of Apparatus
– Example: Separation of sand from a mixture of salt, sand & water
 Set up the apparatus shown below.
 Pour the mixture through __________________ in a ____________________.
 Collect the filtrate in a beaker.
Notes
 The liquid passing through the filter paper is called the ________________.
 The solid collected on the filter paper is called the ________________.
How does it Work?
 The filter paper has tiny holes through which particles of the liquid are able to pass.
 The particles of the solid, being large, cannot pass through these holes and are trapped by
the filter paper.
Practical Application
 The removal of solid impurities by filtration is one of the steps in making
____________________________.
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3.2 Crystallisation
Some background knowledge:
 A solid _____________ in a liquid to form a ________________.
 The solid that dissolves is called a __________ and the liquid is called a _____________.
 A _______________ solution contains the _____________ amount of solute that can be
dissolved at a particular __________________.
Purpose of Crystallisation
 To separate the ____________ (usually a salt) from the _______________ in a solution.
Example: copper (II) sulphate crystals from aqueous copper (II) sulphate solution.
Crystallisation is often used together with:
 Dissolution: _______________ a solute in a solvent.
 Evaporation: a solution is _______________ to dry off the solvent. If all the solvent is
driven off, leaving a solid residue, the process is called evaporation to dryness. A water
bath is used if the solvent is flammable or to prevent damage to the solute.
 Filtration
Procedure & Setup of Apparatus
– Example: Making pure salt from impure salt
 The impure salt contains salt (soluble in water) and impurities (insoluble in water).
Step 1: Dissolution
 Place the given impure salt in a beaker and
add about 50 cm3 of _______________
(this is a suitable solvent).
 _________ while _____________ the
mixture until the salt appears to have
dissolved.
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Step 2: Filtration
 Filter the hot mixture by pouring it through
___________________ in a
_____________________.
 The solid impurities remain on the filter
paper (residue).
 Collect the salt solution (filtrate) in a
beaker.
Step 3: Evaporation
 _________ the filtrate in an
_______________________________ to
evaporate most of the water.
Step 4: Cooling
 Allow the _______________________
solution to cool.
Crystals of the pure salt will form.
 Pour off the cold solution to obtain the
crystals.
 ________ the crystals between filter paper.
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After crystallisation,
 The crystals can be weighed and the percentage purity of the impure salt can be calculated
using:
Mass of salt obtained
Purity =
x 100%
Initial mass of impure salt
Practical Applications of Crystallisation
(1) Manufacture of sugar.
(2) Manufacture of silicon crystals.
3.3 Use of Separating Funnel
Purpose
 To separate two ___________________________.
Example: water and cooking oil.
Procedure & Setup of Apparatus – Example: Separation of water & cooking oil
 Pour the mixture into a ________________________ and leave it standing for some time.
 When the layers of liquids have separated, open the tap to collect each layer in separate
beakers.
How does it Work?
___________________________________________________________________________
___________________________________________________________________________
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3.4 Sublimation
Recall:
 Sublimation is the conversion of a _____________ into a _________________ without
the solid first melting.
Purpose of Sublimation
 To separate __________________________________ from _____________________
______________________.
Examples of solids that sublime are iodine and ammonium chloride.
Procedure & Setup of Apparatus
- Example: Separation of a mixture of ammonium chloride and sodium chloride
 Set up the apparatus shown below.
 _________ the mixture __________________.
 The ammonium chloride _________________ and ___________________ on the cooler
sides of the filter funnel.
Practical Application
 Sublimation is used industrially in the purification of solids that sublime.
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3.5 Simple Distillation
Purpose
 To separate a pure ______________ from a ___________________ of a solute.
It purifies the liquid.
Example: distillation of sea water to obtain pure water.
Procedure & Setup of Apparatus - Example: Obtaining water from sea water
 Set up the apparatus as shown below:
 __________ the sea water in the flask.
 __________ the steam produced using a _____________________.
 Collect the pure liquid water obtained. The salt remains in the flask.
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How does it Work?
 In distillation, the liquid (the solvent) is changed into a gas by __________________.
This gas is pure as other substances are left behind.
So in the sea water distillation example: when the sea water boils, pure gaseous water
(steam) is produced.
 The gas is then _____________.
It condenses into a pure liquid which is called the __________________.
So in the sea water distillation example: steam condenses into liquid water.
 Sea water is a solution of solid salts in water.
The salts, like other solids dissolved in water, cannot be distilled and remain in the flask.
Notes
 The thermometer should be placed _____________ the liquid level in the flask, and next
to the opening into the condenser.
 In the sea water distillation example, the thermometer shows a temperature of 100oC
during the distillation. This is the ____________________________ of water.
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3.6 Fractional Distillation
Purpose
 To separate a mixture of ___________________________.
These liquids are completely soluble in one another. They mix to form one liquid.
Example: fractional distillation of a mixture of ethanol and water.
Procedure & Setup of Apparatus
– Example: Obtaining ethanol from a mixture of ethanol & water
 A ___________
_____________
is used.
Boiling points:
Ethanol: 78oC
Water: 100oC
 Set up the
apparatus
shown on the
right.
 Boil the mixture
of ethanol and
water in the
flask.
 Collect the
liquid that is
distilled out at
78oC (boiling
point of
ethanol).
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How does it Work?
 A fractionating column separates liquids in order of their _____________________.
The liquid with the ____________ boiling point is distilled __________.
The liquid with the ____________ boiling point is distilled __________.
 In the example, the mixture to be separated contains ethanol and water.
Since ethanol has a lower boiling point (78oC) than water (100oC), it boils ___________.
 The ethanol ______________ reaches the top of the fractionating column and is then
___________ as it passes through the _________________.
 It condenses into ____________ ethanol and is collected.
Notes
 The thermometer should be placed ___________ the liquid level in the flask, and next to
the opening into the condenser.
 While the first liquid (in this case, ethanol) is being distilled, the thermometer shows the
boiling point of this liquid (in this case, 78oC).
The liquids with higher boiling points remain in the flask (in this case, only water).
 When almost all of the ethanol has distilled, the water distils. When this happens, the
thermometer shows a temperature of 100oC.
 In the example, can ethanol and water be completely separated? That is, pure ethanol and
pure water will be obtained?
________________________________________________________________________
________________________________________________________________________
Practical Applications
(1) Fractional distillation is used in the petroleum industry to separate __________________
into useful fractions, such as petrol and diesel. In this case the mixture to be separated
contains a number of substances with different boiling points.
(2) Ethanol is produced in the industry by the fermentation of cane sugar (wine making).
The product of fermentation is a mixture of ethanol and water.
Ethanol is obtained from this mixture by fractional distillation.
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3.7 Paper Chromatography
Purpose
 Chromatography is a method of separating and identifying mixtures.
There are several types of chromatography, one of which is ________________________.
Example: separation of the dyes in black ink.
Procedure & Setup of Apparatus
- Example: Separation & identification of dyes in black ink
 Draw a pencil line on a piece
of chromatography paper.
 Place a drop of black ink on
the pencil line.
 The black ink is suspected to
be a mixture of red, blue,
green and orange dyes. So
place drops of these dyes on
the pencil line too.
 Roll the paper into a cylinder
and secure it.
 Place it into a beaker
containing a suitable solvent
for the ink and dyes.
(The chromatography paper can
also be suspended from a glass
rod, such that the end of the filter
paper is dipped into the solvent.)
 The solvent travels up the
paper. The dyes become
separated.
 When the solvent reaches the
top of the paper, take it out of
the beaker and leave it to dry.
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How does it Work?
 In paper chromatography, a suitable _______________ for the mixture to be separated has
to be selected. In the example, the dyes in black ink are to be separated and identified.
 As the solvent travels up the paper, the dyes on the pencil line dissolve in the solvent.
The ______ soluble the dyes are in the solvent, the ___________ they move up the paper.
Hence the dyes move up the paper at _____________________ and become __________.
 A chromatogram is produced:
 Identical dyes travel the _______________________ up the paper.
 Unknown dyes in the black ink can be identified by comparing the chromatogram
obtained for the black ink, with chromatograms of known dyes.
 Results of the experiment show that:
- the black ink is made up of __________ different dyes;
- three of the dyes are the known _________, _________ and __________ dyes;
- there is no _____________ dye in the black ink;
- there is one dye that is different from the four known dyes.
Main Advantage of Chromatography
 It can be used to identify very tiny amounts of substances (10-12 gram or less).
Practical Applications
(1) Chromatography can be used to separate and identify complicated substances such as
__________ and __________________ in food. Government laboratories use
chromatography to check that only approved dyes are used in food.
(2) Analysing the ____________________ of athletes to check if they are using illegal drugs.
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4. Criteria of Purity
4.1 Importance of Purity
 The separation of mixtures into pure substances is important. Chemists need pure
substances to study their properties. Pure substances are used in industry to make useful
products such as food and drugs.
 What is the danger if there are impurities in the food and drugs?
________________________________________________________________________
 The ‘chips’ used in calculators, computers, watches and compact disc players are made of
silicon. Very pure silicon crystals are required.
4.2 Test for Purity
(i) Melting Point Determination
 Impurities ____________ the melting point.
The greater the percentage of impurity, the ______________ the melting point.
 We can find out if a substance is pure by measuring its melting point, and then compare
the measured value to the true melting point recorded in books.
 This method is usually applied to _____________.
 Another way: check if the substance
melts over a _____________ of
temperature. Why?
______________________________
______________________________
______________________________
 Note: The thermometer bulb should
be placed _________________ the
Setup of Apparatus
capillary tube.
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(ii) Boiling Point Determination
 Impurities ____________ the boiling point.
 We can find out if a substance is pure by
distilling it. If the substance is pure, all of it
distils at the _________ temperature, which is
the _________________________.
Otherwise, it will distil over a ___________ of
temperatures.
 This method is usually applied to ____________.
 Note: The thermometer should be placed
___________ the liquid level in the flask.
the substance to be
checked for purity
Setup of Apparatus
(iii) Chromatography
 This method is used for complicated substances and those that cannot be melted or
distilled.
 It is a very sensitive test and is able to detect very _____________________ of impurity.
 As shown by the diagram below, a pure substance gives ______ spot on a chromatogram.
A mixture gives _____________________ on a chromatogram.
Chromatography can also be used to separate and identify colourless substances.
 The chromatogram is sprayed with a ___________________________to show where the
substances are on the paper. The locating agent is a chemical that reacts with the
substances to produce a ________________ product.
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