Titrations: making soluble
salts
Chemistry
Unit
Making salts
Outcome
I can accurately perform a titration, understanding the apparatus and
selecting a suitable indicator to identify the end point.
Keywords
titration
a technique in volumetric analysis that is used to find the exact volumes
of solutions which react with each other
volume
how much 3D space matter occupies, it is often measured in cm³
end point
when just enough solution has been added from the burette to react
with all the solution in the flask in a titration
strong acid
Strong acids ionise completely in water.
meniscus
the curve that exists on the surface of a liquid when it is in a container
Lesson outline
Titrations: making soluble salts
Introduction to titrations
Performing a titration
Introduction to titrations
Explanation
Titration is a method used to completely neutralise a strong
acid with a soluble base (alkali).
Both are completely ionised in aqueous
solution.
This reaction results in the formation of water
and a soluble salt.
Nandalal Sarkar/Shutterstock.com
Introduction to titrations
Check
True or false?
Titration is used to completely neutralise an acid with an insoluble base.
T
True
F
False
Justify your answer
a
Titration does not involve a chemical reaction.
b
An acid is neutralised by a soluble base.
Introduction to titrations
Check
What are the products of a titration between a strong acid and
a strong base?
a
hydrogen
b
water
c
soluble salt
d
insoluble salt
Introduction to titrations
Explanation
Each piece of apparatus in a titration has a specific and
essential function:
● burette: measures and delivers the acid or
base, drop by drop
Nandalaal Sarkar/Shutterstock.com
Introduction to titrations
Explanation
Each piece of apparatus in a titration has a specific and
essential function:
● volumetric pipette: accurately measures a fixed volume of
solution to be titrated
You may not have access to a volumetric pipette and might instead use a measuring
cylinder — note that these are less precise.
Rabbitmindphoto/Shutterstock.com
Introduction to titrations
Explanation
Each piece of apparatus in a titration has a specific and
essential function:
● pipette filler: safely draws the solution into the pipette
Connect Images – Curated/Shutterstock.com
Introduction to titrations
Explanation
Each piece of apparatus in a titration has a specific and
essential function:
● conical flask: allows for safe and effective mixing of
reactants by swirling
NamPu NiNu/Shutterstock.com
Introduction to titrations
Check
What is the primary function of a burette in a titration?
a
to accurately measure a fixed volume of solution
b
to measure and deliver the acid or base, drop by drop
c
to mix reactants by swirling
d
to safely draw solution into a pipette
Introduction to titrations
Check
What is the primary function of a volumetric pipette in a
titration?
a
to accurately measure a fixed volume of solution
b
to measure and deliver the acid or base, drop by drop
c
to mix reactants by swirling
d
to safely draw solution into a pipette
Introduction to titrations
Explanation
A suitable indicator is crucial in titration.
Indicators like phenolphthalein and methyl orange are preferred over
universal indicator because they have a clear and distinct colour change at
the end point of the titration:
● phenolphthalein: colourless in acid, pink in alkali (adding acid to base
— colourless at the end point)
● methyl orange: red in acid, yellow in alkali (adding base to acid —
yellow at the end point)
Introduction to titrations
Check
True or false?
Universal indicator is preferred over phenolphthalein and methyl orange
in titrations.
T True
F False
Justify your answer
Universal indicator has a wide range of colours, with no clear end
a
point.
b
Universal indicator is only useful for showing the numerical value
of pH.
Introduction to titrations
Check
What is the colour change of phenolphthalein when titrating a
base (in flask) with an acid (in burette)?
a
yellow to red
b
red to yellow
c
pink to colourless
d
colourless to pink
Introduction to titrations
Explanation
Titration allows us to add the ‘perfect’ volume of acid to a
base, or vice versa, to achieve complete neutralisation.
This precise method produces soluble salts without any excess
reactants left in the reaction mixture.
Introduction to titrations
Explanation
When making a pure sample of salt, a second titration is
performed without an indicator.
This ensures that the resulting salt is
pure and free from any contamination
by the indicator, using the exact
volumes determined in the first
titration.
Sinhyu Photographer/Shutterstock.com
Introduction to titrations
Check
True or false?
The first titration is performed without an indicator to ensure a pure sample
of salt is obtained.
T
True
F
False
Justify your answer
The first titration must be run with an indicator to measure the volume
a
of solution needed for neutralisation.
b
We don’t use an indicator as it would contaminate our mixture,
skewing our results.
Task A
Introduction to titrations
Practice
1. What is meant by the following terms:
a. strong acid
b. base
c. soluble salt
d. excess reactant
e. end point
2. A pupil adds sodium hydroxide solution, drop by drop, to a solution of hydrochloric
acid and methyl–orange. What colour change will they observe, if any, and why?
3. When making a pure sample of a soluble salt, why must the titration be repeated
after determining the volume of base required to neutralise the acid?
Task A
Introduction to titrations
Feedback
1. What is meant by the following terms:
Strong acid: one that completely ionises in water, meaning it dissociates fully
into its ions.
Base: a substance that can neutralise an acid, making a salt and water.
Soluble salt: a salt that dissolves in a solvent, such as water.
Excess reactant: the substance that is present in a greater amount than
necessary to completely react with the other reactant.
End point: the point at which the reaction between the acid and base is
complete, as indicated by a change in the colour of the indicator used.
Task A
Introduction to titrations
Feedback
2. A pupil adds sodium hydroxide solution, drop by drop, to a
solution of hydrochloric acid and methyl–orange. What colour change would they
observe, if any, and why?
The pupil would observe a colour change from red to orange, and then to
yellow.
Methyl orange is red in acidic solutions (such as hydrochloric acid). As
sodium hydroxide is added, the solution gradually becomes less acidic,
turning orange as it approaches neutral, and then finally turning yellow
when it becomes slightly alkaline.
Task A
Introduction to titrations
Feedback
3. When making a pure sample of a soluble salt, why must the
titration be repeated after determining the volume of base required to neutralise
the acid?
The titration must be repeated without an indicator to produce a pure
sample of the soluble salt.
The initial titration with the indicator determines the exact volume of acid
and base needed to reach the end point.
However, the indicator would contaminate the salt; so the process is
repeated using the same volumes, but without the indicator, to ensure the
resulting salt is pure.
Lesson outline
Titrations: making soluble salts
Introduction to titrations
Performing a titration
Performing a titration
Explanation
When conducting any experiment, never assume that
equipment is ready to use or free of contamination.
Rinsing all equipment with water may seem logical, but:
● tap water contains dissolved salts that can interfere with the reaction
● titration relies on specific volumes; any water used will dilute
reactants and alter the volumes used and recorded.
Performing a titration
Check
True or false?
Tap water is suitable for rinsing chemical apparatus.
T
True
F
False
Justify your answer
a
Rinsing with water will increase the total volume of solution.
b
Tap water contains dissolved salts.
Performing a titration
Explanation
The burette should be rinsed with the chemical it is to be
filled with, not with water.
This ensures no dilution occurs when the burette is filled.
Once filled, always record the initial volume accurately, and to two
decimal places (the last being either a 0 or 5).
Never fill a burette above eye–level (to avoid accidents or spills.)
Performing a titration
Explanation
The volumetric pipette (or measuring cylinder) should also be
rinsed with the solution it will contain.
This prevents dilution by residual water, ensuring accuracy when measuring
the volume.
Be careful when filling the pipette to the marked line.
Performing a titration
Explanation
The conical flask can be rinsed with either water or the same
solution in the volumetric pipette.
Since the volume of the solution is measured before it is transferred to the
flask, any minor dilution from rinsing will not affect the recorded
measurements.
Performing a titration
Check
Why should a burette be rinsed with the chemical it is to be
filled with, rather than water?
a
to prevent contamination
b
to avoid dilution of the chemical
c
to clean the burette more effectively
d
to increase the volume of the chemical
Performing a titration
Check
True or false?
A conical flask can be rinsed with water before being filled with acid or
base (in a titration).
T True
F False
Justify your answer
Any residual water left by rinsing has no real impact on the
a
solution.
b
The volume of solution is measured before it is transferred to the
flask.
Performing a titration
Explanation
The solution is transferred from the volumetric pipette to the
conical flask.
Add a few drops of a suitable indicator,
such as phenolphthalein or methyl
orange.
phenolphthalein indicator
being added.
Performing a titration
Explanation
With the burette set up and the conical flask containing the
solution:
1. The solution is slowly added from the burette to the
solution in the flask, while swirling the flask
continuously.
2. As soon as the indicator changes colour, indicating
that the end point has been reached, the burette
tap is closed.
3. The final volume of the burette is recorded to
determine the volume of solution used.
Connect Images–Curated/Shutterstock.com
Performing a titration
Explanation
Tips for accurate and effective titration:
● Ensure that the solution is added drop by drop as
you approach the end point to avoid overshooting
the reaction.
● Keep swirling the conical flask to mix the solutions
thoroughly, which ensures that the reaction occurs
evenly.
● Always read the meniscus at eye level for both the
initial and final volumes to maintain accuracy.
Ropisme/Shutterstock.com
Performing a titration
Check
When should you stop adding the solution from the burette
to the conical flask?
a
when the solution in the flask becomes cloudy
b
when the indicator changes colour
c
when the solution in the burette is empty
d
when the solution in the flask stops swirling
Performing a titration
Check
Why is it important to swirl the conical flask while adding the
solution from the burette?
a
to cool the solution
b
to prevent the solution from evaporating
c
to speed up the reaction
d
to ensure even mixing of the reactants
Task B
Performing a titration
Practice
Complete a titration to completely neutralise a solution of
hydrochloric acid (0.1 M) and sodium hydroxide (0.1 M) using phenolphthalein
indicator.
Follow the method provided in the additional materials.
Record your results and observations in the table below.
burette readings
final volume (cm³)
initial volume (cm³)
total volume added (cm³)
colour at end point
1st run
2nd run
3rd run
Task B
Performing a titration
Feedback
Complete a titration to completely neutralise a solution of
hydrochloric acid (0.1 M) and sodium hydroxide (0.1 M) using phenolphthalein
indicator.
Record your results and observations in the table below.
Your results may look like this:
burette readings
1st run
2nd run
3rd run
final volume (cm³)
27.50
27.10
26.35
initial volume (cm³)
0.00
1.50
0.65
total volume added (cm³)
27.50
25.60
25.70
colour at end point
colourless
colourless
colourless
Summary
Titrations: making soluble salts
Titration is a method used to completely neutralise an acid with a soluble base
(alkali).
Titrations are performed using strong acids and strong alkalis to accurately
determine reacting volumes.
Strong acids and alkalis are completely ionised in aqueous solution.
Each piece of apparatus in titration has a specific and essential function.
A suitable indicator (not universal indicator) is used to identify the end point of
the titration.
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