CP 5 ‐ Acid-Alkali Titration

Question 1

How can you detect whether a substance is a strong

acid or a strong alkali using universal indicator?

Answer 1

Red - strong acid

Yellow - weak acid

Green - neutral

Light blue - weak alkali

Blue/purple - strong alkali

Question 2

A few drops of methyl orange are added to a beaker
of alkali. What will you observe when adding acid to
this beaker?

Answer 2

Colour changes from yellow to orange then red

Acid - red

Alkali - yellow

Question 3

A few drops of phenolphthalein are added to a
beaker of acid. What will you observe when adding
alkali to this beaker?

Answer 3

Colour change from colourless to pink

Acid - colourless

Alkali - pink

Question 4

How is water formed in a reaction between an acid

and an alkali?

Answer 4

H+ ions from acid react with OH- ions from alkali

Question 5

List the apparatus required to carry out a titration

Answer 5

• Burette
• Conical flask
• Clamp stand
• Pipette
• Small funnel
• White tile

Question 6

Describe how to set up a titration

Answer 6

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.

Question 7

Why should you rinse the burette and pipette with

the solutions they will contain before filling them?

Answer 7

To wash out any other unwanted ions

from the apparatus

Question 8

After the apparatus has been set up, describe how to

carry out a titration

Answer 8

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.

Question 9

What safety precautions should be taken when

carrying out a titration?

Answer 9

• 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…

Question 10

Why is an indicator used in a titration?

Answer 10

To show when the end point has been

reached

Question 11

Why is a white tile used in a titration?

Answer 11

The white tile is placed under the
reaction mixture to make the colour
change easier to see

Question 12

Why should the conical flask be swirled during a

titration?

Answer 12

To ensure the solution is completely

mixed

Question 13

What is the purpose of repeating a titration?

Answer 13

To obtain concordant results, allow a
mean titre to be calculated, and reduce
the effect of random error

Question 14

Why is a trial titre carried out?

Answer 14

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.

Question 15

What are concordant results?

Answer 15

Titres which are within 0.20cm3

(or 0.10cm3) of each other

Question 16

How do you calculate the mean titre?

Answer 16

Add the 2 concordant results and divide

by 2

Question 17

What is the end point?

Answer 17

The point when the indicator first

permanently changes colour

Question 18

Why is a volumetric pipette used to measure the

volume of acid or alkali added to the conical flask?

Answer 18

Greater accuracy than a measuring

cylinder

Question 19

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)

Answer 19

• 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

Question 20

Define titre?

Answer 20

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.