Titration

Question 1

what is the titration practical?

Answer 1

a practical method used to measure the volume (or ‘titre’) of acid needed to neutralise a particular volume of alkali, or vice-versa

Question 2

what is a volumetric pipette used for?

Answer 2

measures out 25cm3 very accurately (not good for any other measurement)

Question 3

what is a burette used for in titration?

Answer 3

measures any volume to the nearest 0.05cm3

Question 4

where does the acid and alkali go in titration?

Answer 4

• the acid is known, so it goes into the burette
• the alkali is unknown, so it goes into a conical flask

Question 5

what is the complete method for the titration practical?

Answer 5

1. use a volumetric pipette to place 25cm3 of the unknown alkali into a conical flask
2. add a few drops of either methyl orange or phenolphthalein indicator to the flask
   (universal indicator doesn’t work because it changes colour too gradually)
3. fill a burette with known acid and clamp it above the conical flask
4. measure the initial volume of known acid on the burette, to the nearest 0.05cm3
5. use the burette to add acid into the conical flask drop-by-drop and swirling the flask
6. close the burette tap as soon as the colour in the conical flask changes - the start colour will be the alkaline colour, the end colour will be the acidic colour (because the last drop of acid always has a tiny amount more than is needed to neutralise)
7. measure the final volume of known acid on the burette, to the nearest 0.05cm3
8. calculate titre (final volume - initial volume)
9. repeat to get concordant (within 0.2cm3) titres

Question 6

how do you record titration results?

Answer 6

• in a table, with every volume to the nearest 0.05cm3
• the mean titre is calculated based on the concordant titres (within 0.2cm3)

Question 7

how do you do titration calculations?

Answer 7

you use the mole ratio in the balancing numbers from the reaction equation to convert:

• from moles of a substance you know lots about (e.g. the known acid)
• to moles of a substance you don’t know much about (e.g. the unknown alkali)

Question 8

what is the method of titration calculation?

Answer 8

1. calculate the moles of X
2. use the mole ratio from the equation to get the moles of Y
3. calculate the concentration of Y

(and vice versa)