Practicals

Question 1

Describe the method of making up a standard volumetric solution for an acid-base titration

Answer 1

1. Calculate the mass of required substance needed to produce
   250 cm3

of a 0.100 mol dm-3 solution.
2. Weigh a clean dry weighing bottle (or weighing boat) on a 2dp
balance.

3. Place the weighing bottle on the pan of a digital balance and
   zero the balance. Using a spatula, place (approximately) the
   calculated mass of required substance into the bottle.
4. Remove from the balance, set to zero and re-weigh the weighing
   bottle and its contents, recording the value.
5. Pour the contents of the weighing bottle into a clean, glass
   beaker and re-weigh the weighing bottle, recording the value
6. Calculate the mass of required substance that you have
   transferred to the beaker [difference in two mass values].
7. Add approximately 100 cm3
   of deionised (or distilled) water to
   the beaker containing the solid. Use a glass rod to stir the
   contents of the beaker until all the solid has dissolved.
8. Using a funnel, pour the contents of the beaker into a 250 cm3
   volumetric flask. Using further deionised (or distilled) water in a
   wash bottle, wash out the beaker and funnel, transfering all
   washings into the volumetric flask.
9. Make the volumetric flask up to the graduated mark by carefully
   adding deionised water from a wash bottle.
10. Stopper the volumetric flask and invert to combine thoroughly (shake)

Question 2

How would you do a titration?

Answer 2

1. Pour approximately 100cm3
   of the standard
   solution of known concentration into a beaker.
2. Fill the burette with the standard solution of
   known concentration.
3. Pour approximately 100cm3
   of the solution with
   unknown concentration into a second beaker.
4. Using a pipette filler and pipette to transfer
   exactly 25cm3
   of solution into a 250cm3
   conical
   flask.
5. Add two to three drops of phenolphthalein
   indicator to the solution in the conical flask and
   note the initial colour of the indicator.
6. Record the initial burette reading (bottom of meniscus)
7. Titrate the contents of the conical flask by
   adding solution to it from the burette until the
   indicator undergoes a definite, permanent
   colour change. Record the final burette reading
   in your table of results. Calculate the titre
   volume (change in volume in the burette).
8. Repeat, calculate and record the volume of
   solution used in the titration in a table (titre
   volume). Repeat until two concordant results
   are obtained. Record all of the results that you obtain.

Question 3

Describe the method of ‘measuring and enthalpy change’

Answer 3

For: anhydrous copper sulfate + aq&raquo_space;> copper sulfate solution