EXPERIMENTAL TECHNIQUES
AND CHEMICAL ANALYSIS
[UNIT 12]
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Table of Contents
Experimental Design ................................................................................................................................. 3
Planning an Experimental Investigation....................................................................................... 3
Selecting The Correct Apparatus ................................................................................................ 3
Variables................................................................................................................................................. 4
Sources of Error ................................................................................................................................. 4
Separation & Purification ...................................................................................................................... 5
Separation Using Different Solvents .............................................................................................. 5
Filtration................................................................................................................................................ 5
Crystallization ...................................................................................................................................... 6
Simple Distillation.............................................................................................................................. 6
Fractional Distillation ....................................................................................................................... 7
Testing Purity with Melting Point Analysis ................................................................................ 8
Paper Chromatography ........................................................................................................................... 8
Steps ............................................................................................................................................................ 8
Interpreting Chromatograms............................................................................................................ 9
Dye Compositions ............................................................................................................................... 9
Pure & Impure Substances ......................................................................................................... 10
Rf Values ................................................................................................................................................. 10
Examples ............................................................................................................................................. 10
Localising Agents ................................................................................................................................. 10
Identification of Ions & Gases ............................................................................................................ 11
Identification of Cations ................................................................................................................... 11
Flame Tests ........................................................................................................................................ 11
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Using NaOH(aq) & NH3(aq) ................................................................................................................. 12
Using NaOH(aq) (Aqueous Sodium Hydroxide) ...................................................................... 12
Using NH3(aq) (Aqueous Ammonia) ........................................................................................... 13
Identification of Anions .................................................................................................................... 14
Carbonate Ions (CO3-) ................................................................................................................... 14
Other Anions ..................................................................................................................................... 14
Test for Gases ....................................................................................................................................... 15
Quantitative Analysis: Acid-Base Titration ................................................................................. 15
Apparatus .............................................................................................................................................. 15
Steps ......................................................................................................................................................... 16
Caution When Measuring ................................................................................................................. 16
Glossary ....................................................................................................................................................... 17
Experimental Design .......................................................................................................................... 17
Separation & Purification ............................................................................................................... 17
Chromatography ................................................................................................................................. 18
Identification of Ions & Gases ........................................................................................................ 18
Quantitative Analysis: Acid-Base Titration ............................................................................. 18
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Experimental Design
Planning an Experimental Investigation
Selecting The Correct Apparatus
In the 2nd step of the flowchart, we “draw up experiments to plan the hypothesis”.
When we do this, we must first choose the apparatus we will use for these
experiments.
The type of apparatus to use in the experiments depend on the scale and accuracy of
the result required.
The scale of an experiment refers to the amount of product needed.
Accuracy refers to the closeness of a value to the “true” value.
We must also choose apparatus which give us precise results.
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Quantity
Apparatus
Stopwatch
Time
Universal Indicator
0.01 seconds (digital stopwatch)
Low accuracy (low resolution)
pH
Digital Probe
Thermometer
Digital Thermometer
High accuracy (high resolution)
Temperature
Simple Balance
Complex Balance
Accuracy
Measured
1‫ﹾ‬C
0.1‫ﹾ‬C
Low accuracy (caused by low resolution)
Mass
High accuracy (higher resolution)
Spatula
Approximate value
Burette
Accurate for variable volumes
Volumetric Pipette
Measuring Cylinder
Volume
Gas syringe
Most accurate for fixed volumes
Sufficient accuracy
Sufficient accuracy
Variables
Sources of Error
Error
Random Errors
Unpredictable variations in results usually due to human error.
Systematic Errors
Consistent errors due to experimental design or apparatus.
Anomalous Error
Zero Error
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Unusual or unexpected occurrence causing result to deviate
from normal.
Measuring instrument error where start value is not 0.
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Separation & Purification
Separation Using Different Solvents
We can use the difference in solubilities to separate a mixture of solids.
Step 1:
To separate a mixture with 2 solids, we must choose a solvent in which one solid is
soluble and the other is insoluble.
Step 2:
We can then filter the solution which will leave us with a residue in the filter paper.
We can dry this residue to give us the insoluble solid.
Step 3:
We can now get the soluble solid, which is in the solution, we can simply evaporate
the solvent to get the soluble solid.
Filtration
This is to separate an insoluble solid from a liquid.
Step 1:
Pass the liquid with insoluble solid through filter paper.
Step 2:
The insoluble solid filtered out with filter paper is called “residue”.
The filtered liquid is called “filtrate”.
Note: If the insoluble solid is extremely fine, we use a Buchner funnel.
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Crystallization
This method is used to remove water from a solution containing an ionic compound.
The process works because the boiling point of water is lower than a salt.
Step 1:
Carefully heat the sample in an evaporating basin or place the basin by placing it
over a beaker of boiling water.
Larger crystals can be obtained by evaporating a little water and leave solution to
cool and evaporate at room temperature.
Step 2:
Dry the crystals between filter paper.
Simple Distillation
Simple distillation is used to separate the solvent from the solution containing a
dissolved solid.
The liquid’s boiling point is usually less than that of the dissolved solid.
The liquid solvent is also volatile making it easy to evaporate in a distillation flask.
Before The Process…
We can add “anti-bumping granules” to the liquid, this helps prevent formation of
large bubbles in liquid when boiling.
Step 1:
Set Bunsen burner to boil the liquid.
Step 2:
The liquid boils and goes through the condenser where it comes out into a flask or
beaker without the salt (distillate).
The salt can be obtained from the distillation flask as it is left behind.
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Fractional Distillation
This is used to separate liquids from a mixture of 2 or more miscible liquids.
The concept is based on that the 2 liquids have 2 different boiling points.
Since the difference of boiling point is not as high as with simple distillation, we
make use of a fractionating column which makes it so that the most volatile liquid is
distilled first.
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Testing Purity with Melting Point Analysis
A pure substance is made of a single chemical element or compound. It melts and
boils at a definite temperature.
We can simply measure the melting point of the substance we get and compare it to
the standard value.
If it is same, then the substance is pure, if not, then it is impure.
Paper Chromatography
This is used to separate 2 solids which are dissolved in a liquid and have different
solubilities.
For the solids to separate, they must:
1. Have 2 different solubilities in the solvent.
2. Have different degrees of attraction for the filter paper.
Note that the solids travel according to their solubility levels.
Solids with highest solubility travel the farthest & the ones with the lowest solubility
travel the least.
This method was originally used to separate soluble pigments using filter paper.
Steps
1. Take some chromatography paper, draw a
pencil line (baseline).
2. Put a drop of each solution you want to
separate on the baseline an appropriate
distance away from each other.
3. Place the paper in a beaker with water, the
paper must touch the water slightly.
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4. Leave the apparatus like shown (side) for
about an hour or so (google has many
answers lol).
5. Look at the paper, it would have different
colours at different levels (just use the
diagrams, too hard to explain).
→ This is because the solids separate
according to their solubility in the
solution.
6. Remember to stop the run before the solvent
front reaches the top.
7. Dry the paper to get a “chromatogram”.
Tip: Question about what went wrong appear every now
and again! (Paper 6)
Interpreting Chromatograms
We can use chromatograms to tell:
1. What an unknown dye is made of (by comparing with other dyes).
2. Weather a substance is pure or not.
Dye Compositions
Let’s say we have a chromatogram for dyes X, A, B, and C.
By looking at the diagram, we can see that the orange
pigment is shared between X & C.
We can also see that the green pigment is shared between X
& A.
This is basically how we use other dyes to figure out the dye
composition of an unknown dye.
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Pure & Impure Substances
We will be using the cryptogram at the right for explanation.
Pure substances are made up of only one dye/substance.
Impure substances are made up of 2 or more dyes/substances.
Using the definitions, we can say that substance X is impure, but
substances A, B, and C are pure.
Rf Values
This is a ratio of the distance travelled by the solute and the distance travelled by the
solvent:
𝑅𝑓 =
𝐷𝑖𝑠𝑡𝑐𝑎𝑛𝑐𝑒 𝑀𝑜𝑣𝑒𝑑 𝐵𝑦 𝑇ℎ𝑒 𝑆𝑢𝑏𝑠𝑡𝑎𝑛𝑐𝑒
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑀𝑜𝑣𝑒𝑑 𝐵𝑦 𝑆𝑜𝑙𝑣𝑒𝑛𝑡 𝐹𝑟𝑜𝑛𝑡
Examples
Example 1 (B)
𝑅𝑓 =
8
= 0.5
16
Example 2 (C)
𝑅𝑓 =
14
= 0.875
16
Tip: The Rf value is always between 1 and 0 as it is a ratio meaning
1.2 is not valid (0.00 ≤ 𝑥 ≤ 1.00)
Localising Agents
These are compounds which react with the invisible & colourless spots to produce a
coloured product which can be seen.
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Identification of Ions & Gases
Identification of Cations
Flame Tests
Steps
1. Heat a nichrome wire probe.
2. Dip the wire in HCl (Hydrochloric Acid).
3. Dip the wire into the salt which is to be tested.
4. Hold the sample at the edge of a blue Bunsen burner flame.
5. The flame will now change the colour accordingly.
Flame Test Colours to Remember
Cation
Flame
Colour
Lithium
Sodium
Potassium
Calcium
Barium
Copper (II)
Li+
Na+
K+
Ca2+
Ba2+
Cu2+
Red
Yellow
Lilac
Orange
Light
Red
Green
Blue Green
Alternate Method
An alternate method is using a wooden splint:
1. Dip wooden slip into solution for a long period of time.
2. Place the splint into a Bunsen burner flame.
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Using NaOH(aq) & NH3(aq)
This is done using precipitation reactions because not all cations can be tested using a
flame test.
This method does not work for group 1 & 2 metals due to their high reactivity.
Using NaOH(aq) (Aqueous Sodium Hydroxide)
This is when we add NaOH solution to the solution with a metal cation.
This leads to the formation of an insoluble metal hydroxide from a precipitation
reaction.
Colours & Reactions
Cation
Result When NaOH(aq) is added
Aluminium
→ White precipitate
[Al+]
→ Redissolves in excess aqueous NaOH to give colourless solution
Ammonium
→ No precipitate
[NH4+]
→ Produces ammonia when heated
Calcium
→ White precipitate
[Ca2+]
→ Insoluble in excess aqueous NaOH
Chromium (III)
→ Green precipitate
[Cr3+]
→ Redissolves in excess aqueous NaOH
Copper (II)
→ Light blue precipitate
[Cu2+]
→ Insoluble in excess aqueous NaOH
Iron (II)
[Fe2+]
→ Green precipitate
→ Insoluble in excess aqueous NaOH
→ Starts to turn brown near the surface if left to stand
Iron (III)
→ Red brown precipitate
[Fe3+]
→ Insoluble in excess aqueous NaOH
Zinc
→ White precipitate
[Zn2+]
→ Redissolves in excess aqueous NaOH to give colourless solution
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Equations (Examples)
Iron (II):
𝐼𝑟𝑜𝑛(𝐼𝐼𝐼)𝐶ℎ𝑙𝑜𝑟𝑖𝑑𝑒 + 𝑆𝑜𝑑𝑖𝑢𝑚 𝐻𝑦𝑑𝑟𝑜𝑥𝑖𝑑𝑒 → 𝐼𝑟𝑜𝑛(𝐼𝐼𝐼)𝐻𝑦𝑑𝑟𝑜𝑥𝑖𝑑𝑒 + 𝑆𝑜𝑑𝑖𝑢𝑚 𝐶ℎ𝑙𝑜𝑟𝑖𝑑𝑒
𝐹𝑒𝐶𝑙3(𝑎𝑞) + 3𝑁𝑎𝑂𝐻(𝑎𝑞) → 𝐹𝑒(𝑂𝐻)3(𝑠) + 3𝑁𝑎𝐶𝑙(𝑎𝑞)
Copper (II):
𝐶𝑜𝑝𝑝𝑒𝑟(𝐼𝐼)𝐶ℎ𝑙𝑜𝑟𝑖𝑑𝑒 + 𝑆𝑜𝑑𝑖𝑢𝑚 𝐻𝑦𝑑𝑟𝑜𝑥𝑖𝑑𝑒 → 𝐶𝑜𝑝𝑝𝑒𝑟(𝐼𝐼)𝐻𝑦𝑑𝑟𝑜𝑥𝑖𝑑𝑒 + 𝑆𝑜𝑑𝑖𝑢𝑚 𝐶ℎ𝑙𝑜𝑟𝑖𝑑𝑒
𝐶𝑢𝐶𝑙2(𝑎𝑞) + 2𝑁𝑎𝑂𝐻(𝑎𝑞) → 𝐶𝑢(𝑂𝐻)2(𝑠) + 2𝑁𝑎𝐶𝑙(𝑎𝑞)
Using NH3(aq) (Aqueous Ammonia)
This is when we add aqueous ammonia to the solution with metal cations.
Cation
Result When NH3(aq) is added
Aluminium
→ White precipitate
[Al+]
→ Insoluble in excess aqueous NH3
Ammonium
[NH4+]
Calcium
[Ca2+]
No Reaction…
→ No precipitate or very slight precipitate
Chromium (III)
→ Green precipitate
[Cr3+]
→ Insoluble in excess aqueous NH3
Copper (II)
→ Light blue precipitate
[Cu2+]
→ Soluble in excess aqueous NH3 to produce dark blue solution
Iron (II)
[Fe2+]
→ Green precipitate
→ Insoluble in excess aqueous NH3
→ Starts to turn brown near the surface if left to stand
Iron (III)
→ Red brown precipitate
[Fe3+]
→ Insoluble in excess aqueous NH3
Zinc
→ White precipitate
[Zn2+]
→ Redissolves in excess aqueous NH3 to give colourless solution
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Identification of Anions
Carbonate Ions (CO3-)
Test for carbonate relies on the fact that it produces CO2 gas when reacted with
acid.
In the experiment above, we react a carbonate with acid to produce CO2 gas.
The gas passes through the delivery tube and into the test tube with limewater.
When CO2 passes into the limewater, it changes colour from clear to cloudy/milky.
This proves that there are carbonate ions present in the tablet.
Other Anions
Anion
Chloride
Bromide
Iodide
Sulfate
Sulfite
Nitrate
(In solution)
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Test
→ Add nitric acid (to remove CO3-)
→ Add silver nitrate
Result
White ppt
Cream ppt
Yellow ppt
→ Add nitric acid (to remove CO3-)
White ppt
→ Add barium nitrate
(Barium Sulphate)
→ Add dilute HCl
Purple KMnO4
→ Add aqueous potassium manganate (VIII)
solution decolorises
→ Add aqueous NaOH
→ Add aluminium foil and warm
→ Test for ammonia
Ammonia gas is
given off
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Test for Gases
Gas
Test
Result
Hydrogen
Place lighted splint at neck of test tube
Oxygen
Place glowing splint in test-tube of gas
Carbon Dioxide Bubble it through limewater
Chlorine
Use damp blue litmus paper
Ammonia
Use damp red litmus paper
Sulfur Dioxide
Squeaky pop sound
produced
Splint relights
Limewater turns from
clear to cloudy/milky
Paper changes to red &
turns white
Paper changes to blue
Pass it over a filter paper dampened
with acidified KMnO4
The filter paper
decolorises (purple to
colourless)
Quantitative Analysis: Acid-Base Titration
This is a method of quantitative chemical analysis where an acid is slowly added to a
base until it is neutralised.
Apparatus
For this, you need:
→ Burette
→ Filler
→ Volumetric Pipette (highly accurate)
→ Stand
→ Conical Flask
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Steps
1. Fill the burette with acid.
2. Fill the conical flask with a fixed volume of base using a volumetric pipette or filler.
3. Clamp the burette to the stand vertically.
4. We use an indicator to determine the point at which the alkali has been
neutralised.
5. Slowly add the acid from the burette dropwise as we approach the end point.
6. Swirl the conical flask as we add the acid to ensure that everything has reacted.
7. We will know if the solution is neutralised when the indicator added is in neutral
state (methyl orange is orange and phenolphthalein is colourless).
Caution When Measuring
When taking readings from the burette, make sure that you read the lower meniscus
and read with the eye parallel to burette.
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Glossary
Experimental Design
Accuracy: How close a value is to the true value
Precision: The degree to which repeat measurements are consistent
Resolution: The smallest division of an instrument
Calibration: Process of checking the device gives accurate values by using it to read
samples with known values
Control Variables: Variable which is kept same throughout the investigation
Independent Variables: Variable which is altered in an investigation
Dependant variables: Variable which is measured during an investigation
Separation & Purification
Filtration: Used to separate liquid from solid using filter paper
Distillation: Method to separate liquid from dissolved solids
Fractional Distillation: Used to separate liquids with different boiling points
Crystallization: Process of forming crystals from saturated solution
Solution: Formed when a substance dissolves into another substance
Residue: Solid left behind after filtration in filter paper.
Filtrate: Liquid which passes through the filter paper in filtration
Anti-bumping granules: small granules which help reduce bubble size formed when a
liquid boils
Distillate: liquid collected in receiving flask during distillation
Pure substance: Single chemical or compound & boils/melts at definite temperatures
Mixture: 2+ substances mixed yet not chemically combined
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Chromatography
Paper Chromatography: Used to separate components of soluble substances based on
their rate of migration in a solvent on sheets of paper
Solvent Front: Moving boundary of the liquid solvent that moves up the paper
Chromatogram: Result of a paper chromatography run
Rf Value: The ratio of distance travelled by the solute to the distance travelled by
solvent front
Localizing Agent: A compound which reacts with invisible, colourless spots separated
by chromatography to give a coloured product which is visible
Identification of Ions & Gases
Qualitative: Process used to determine the presence or absence of a substance in a
sample
Cation: Positive ion which would be attracted to the cathode in electrolysis
Anion: Negative ion which would be attracted to the anode in electrolysis
Precipitate (ppt): Insoluble salt formed during a precipitation reaction
Precipitation Reaction: Reaction where insoluble salt is prepared from solutions of 2
soluble salts
Quantitative Analysis: Acid-Base Titration
Quantitative: Process used to find the amount of a substance in a sample
Acid-Base Titration: Method where acid is slowly added to base until neutralised
Titre: Volume of solution added from burette during a titration
Indicator: Substance which changes colour when added to acidic/alkaline solution
✨🥳🎉 (p≧▽≦p) The End! q(≧▽≦q) 🎉🥳✨
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