CP 5 ‐ Acid-Alkali Titration Flashcards
How can you detect whether a substance is a strong
acid or a strong alkali using universal indicator?
Red - strong acid
Yellow - weak acid
Green - neutral
Light blue - weak alkali
Blue/purple - strong alkali
A few drops of methyl orange are added to a beaker
of alkali. What will you observe when adding acid to
this beaker?
Colour changes from yellow to orange then red
Acid - red
Alkali - yellow
A few drops of phenolphthalein are added to a
beaker of acid. What will you observe when adding
alkali to this beaker?
Colour change from colourless to pink
Acid - colourless
Alkali - pink
How is water formed in a reaction between an acid
and an alkali?
H+ ions from acid react with OH- ions from alkali
List the apparatus required to carry out a titration
- Burette
- Conical flask
- Clamp stand
- Pipette
- Small funnel
- White tile
Describe how to set up a titration
Use a pipette to add a known volume of
alkali to a conical flask.
Add a few drops of indicator.
Fill the burette with acid using a funnel.
Why should you rinse the burette and pipette with
the solutions they will contain before filling them?
To wash out any other unwanted ions
from the apparatus
After the apparatus has been set up, describe how to
carry out a titration
Open the tap of the burette to slowly add
the solution to the conical flask, swirling
to mix. Close the tap when the end point
is reached. Record the volume. Repeat.
What safety precautions should be taken when
carrying out a titration?
- Clear up spillages or broken glassware
- Wear safety goggles and gloves
- Fill burette below eye level using a funnel
-Be aware of the harmful effects of the chemicals
used e.g. irritant, corrosive…
Why is an indicator used in a titration?
To show when the end point has been
reached
Why is a white tile used in a titration?
The white tile is placed under the
reaction mixture to make the colour
change easier to see
Why should the conical flask be swirled during a
titration?
To ensure the solution is completely
mixed
What is the purpose of repeating a titration?
To obtain concordant results, allow a
mean titre to be calculated, and reduce
the effect of random error
Why is a trial titre carried out?
To quickly check that the end-point can
be reached with the concentrations and
volumes being used.
To find the rough volume required to
reach end-point.
What are concordant results?
Titres which are within 0.20cm3
(or 0.10cm3) of each other
How do you calculate the mean titre?
Add the 2 concordant results and divide
by 2
What is the end point?
The point when the indicator first
permanently changes colour
Why is a volumetric pipette used to measure the
volume of acid or alkali added to the conical flask?
Greater accuracy than a measuring
cylinder
If you know the volume of acid required to neutralise an
alkali, how could you calculate the concentration of the acid,
given the alkali concentration and volume? (Higher)
- Calculate the number of moles of the alkali using the known volume
and concentration - Use the chemical equation to work out the ratio of acid and alkali
that react and hence work out how many mole of acid have reacted - Divide the moles of acid by the volume used in neutralisation
Define titre?
The difference between the reading at the start and the final reading gives the volume of acid (or alkali) added. This volume is called the titre.
