Making a standard solution

Question 1

Equipments

Answer 1

 weighing bottle or boat
 250 cm3 volumetric (graduated) flask
 sodium hydrogensulfate solid
 filter funnel
 spatula
 deionised or distilled water in a wash bottle
 250 cm3 beaker
 glass rod
 digital mass balance (reading to 2 or 3 decimal places).

Question 2

Suggested method
The task is to prepare 250 cm3 of a solution of sodium hydrogensulfate with a known concentration in the range 0.090 to 0.110 mol dm–3

Answer 2

a) Calculate the mass of sodium hydrogensulfate solid needed to produce 250 cm3 of a
0.100 mol dm–3 solution. Show your working. If you are using the anhydrous solid, the mass to weigh out will be between 2.7 and 3.3 g, and if you are using the monohydrate, the mass to weigh out should be between 3.1 and 3.8 g
b) Weigh a clean dry weighing bottle (or weighing boat).
c) Place the weighing bottle on the pan of a digital balance and, using a spatula, place into
the bottle approximately the mass of sodium hydrogensulfate that you have calculated to be
necessary.
d) Weigh the weighing bottle and its contents accurately and record the precise mass.
e) Pour the contents of the weighing bottle into a beaker and re-weigh the weighing bottle
(which may still contain traces of sodium hydrogensulfate).
f) Calculate the mass of sodium hydrogensulfate that you have transferred. Remember to record
all weighings to the resolution of the balance that you have used.
g) Add approximately 100 cm3 of deionised (or distilled) water to the beaker containing the
solid and use a glass rod to stir the contents of the beaker until all of the sodium
hydrogensulfate dissolves.
h) Using a funnel, pour the contents of the beaker into a 250 cm3 volumetric (graduated)
flask and then using the wash bottle rinse the beaker and funnel into the same volumetric
flask. Rinse the glass rod into these washings.
i) Make the volumetric flask up to the graduated mark by carefully adding deionised water
from the wash bottle. You will need to be careful so that you do not over-shoot the mark.
j) Stopper the volumetric flask and shake it thoroughly to mix the contents of the flask.
k) Calculate the exact concentration in mol dm–3 of your solution quoting the value to the
appropriate precision. Show all of your working.

Question 3

Make up a volumetric solution and carry out a simple acid-base titration:
To determine the concentration of a solution of sodium hydroxide by titration using a sodium hydrogensulfate solution that has a known concentration
Equipment

Answer 3

You are provided with the following:
 burette
 stand and clamp
 25 cm3 pipette
 pipette filler
 two 250 cm3 conical flasks
 two 250 cm3 beakers
 funnel
 wash bottle
 phenolphthalein indicator
 sodium hydrogensulfate solution
 sodium hydroxide solution.

Question 4

Make up a volumetric solution and carry out a simple acid-base titration:
To determine the concentration of a solution of sodium hydroxide by titration using a sodium hydrogensulfate solution that has a known concentration
Method

Answer 4

a) Pour approximately 100 cm3 of the sodium hydrogensulfate solution into a clean, dry beaker that is labelled ‘sodium hydrogensulfate’. Use a small volume of this solution to rinse the burette before filling it with the sodium hydrogensulfate solution.
b) Pour approximately 100 cm3 of the sodium hydroxide solution into a second clean, dry beaker labelled ‘sodium hydroxide’.
c) Rinse a 25 cm3 pipette with the sodium hydroxide solution provided and then, using a pipette filler, pipette exactly 25.0 cm3 of sodium hydroxide solution into a 250 cm3 conical flask (which has been rinsed with deionised water).
d) Add two to three drops of phenolphthalein indicator to the solution in the conical flask and note the colour of the indicator in alkali.
e) Before you start to titrate, construct a table ready to record your results.
f) Record the initial burette reading. Make sure that all your burette readings are to the
appropriate precision.
g) Titrate the contents of the conical flask by adding sodium hydrogensulfate solution to it from
the burette. Add the sodium hydrogensulfate solution slowly, swirling the flask gently to mix the solution. Add the sodium hydrogensulfate solution dropwise near the end-point until the indicator undergoes a definite colour change; this is the end-point of the titration. Record the colour change in your results. Record the final burette reading in your table of results.

h) Calculate and record in your table of results the volume of sodium hydrogensulfate solution used.
i) Repeat the titration until you obtain two results which are concordant. You should normally carry out at least three titrations. Record all of the results that you obtain.
j) Calculate and record the mean volume of sodium hydrogensulfate solution used in the titration. Show your working.
k) Use your results to calculate the concentration of the sodium hydroxide. Show your working.