Titrations

Question 1

weighing by difference method (titration)

Answer 1

1) Weigh the weighing boat containing the required mass of solid
on a 2 dp balance
2) Transfer to beaker
3) Reweigh empty weighing boat
4) Record the difference in mass

Question 2

making a solution method (titrations)

Answer 2

1) Pour solution into a 250cm3 graduated flask via a funnel
2) Add washings using distilled water
3) Make up to the 250cm3
4) Invert flask several times to ensure uniform solution.

Question 3

why shouldn’t you put hot solutions in the graduated flask

Answer 3

because the heat would cause the flask to expand and the volume would then be incorrect

Question 4

Diluting a solution (titrations)

Answer 4

1) Pipette 25.0cm3 of original solution into a 250cm3 volumetric flask
2) make up to the mark with distilled water using a dropping
pipette for last few drops
3) Invert flask several times to ensure uniform solution.

Question 5

why is a volumetric pipette more accurate than a measuring cyclinder

Answer 5

it has a smaller uncertainty

Question 6

general method for titrations

Answer 6

1) rinse equipment (burette with acid, pipette with alkali, conical flask with distilled water)

2) pipette 25 cm3 of alkali into conical flask

3) touch surface of alkali with pipette ( to ensure correct amount is added)

4) add acid solution from burette

5) make sure the jet space in the burette is filled with acid

6) add a few drops of indicator and refer to colour change at end point

7) use a white tile underneath the flask to help observe the colour change

8) add acid to alkali whilst swirling the mixture and add acid drop wise at end point *

9) note burette reading before and after addition of acid

10) repeat titration until at least 2 concordant results are obtained

Question 7

why should the burette be rinsed out with substance that will be
put in it

Answer 7

because If it’s not rinsed out the acid or alkali added may be
diluted by residual water in the burette = lead to the conc of the substance being lowered and a larger titre being delivered.

Question 8

why should you not leave a funnel in the burette

Answer 8

because small drops of liquid might fall from the funnel during the titration leading to a false burette reading (would give a lower titre volume)

Question 9

why should we make sure the jet space in the burette is filled

Answer 9

if it isn’t filled properly before titrating, it’ll lead to errors if it fills during the titration = larger than expected titre reading.

Question 10

why should the sides of the conical flask be washed with distilled water

Answer 10

so that all the acid on the side is washed into the reaction
mixture to react with the alkali