Volumetric analysis

Volumetric analysis is the measurement (in volumes) of solutions by titration experiments. Thus via the titration method we are able to determine the concentration of a substance in a given solution. Volumetric analysis is very important as with medicines, it is very important to know the concentration of the medicine in order to make sure the required dosage is being used and to limit the chances of overdoes. Volumetric analysis also helps us determine factors such as the amount of carbon dioxide in soft drinks and the amount of alkali in a cleaning solution, or even the amount of acid in a bottle of vinegar.

Materials and Apparatus:

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* Burette

* 25cm� pipette

* Retort stand

* Clamp

* Conical flask

* Pipette filler

* Phenolphthalein

* Sulphuric acid

* 25cm� of 0.1 ml/dm� Sodium hydroxide

Procedure:

1. Wash all equipment 3 times with distilled water

2. Rinse the burette with a little of the acid and then fill it up

3. Rinse the pipette with a little of the base before accurately transferring 25.0cm� of it to a titration flask.

4. Place 2 to 3 drops of an appropriate indicator in the flask and titrate rapidly, until the end-point is reached

5. repeat experiment 2-3 times until you obtain precise results

Precautions

* Avoid parallax error when taking readings, by placing eyes perpendicular to the scale.

* In order to get accurate results make sure to titrate slowly and immediately stop once there is a colour change. Shaking the beaker from time to time also helps.

Observations:

As the HCL is titrated into the beaker containing NaOH, there is a visible colour change. The solution alters from colourless to a pale pink, once a suitable amount of HCL is added.

RESULTS

Table no.1

Experiment no.

Amount of titrate needed in ml

1

12.5

2

12.7

3

13.0

4

12.4

Calculations:

1. The concentration of NaOH=0.25mol dm��

2. Number of moles in 25.0cm� of NaOH=the volume the concentration which is 0.25 = 0.00625

3. The ratio of NaOH to H2SO4 = 2:1

4. Number of moles in the average acid titre = 0.00625

=0.003125

5. Concentration of H2SO4 = =

= 0.000246

6. A r of H2SO4 = 2(1)+32+4(16) =98

7. Concentration of H2SO4 =Concentration in mol dm�� A r = 0.00025

=0.0245g dm��

Equations

Chemical equation: 2NaOH (aq) + H2SO4 (aq) �Na2SO4 (aq) +2H2O (l)

Word equation: sodium hydroxide+ sulphuric acid � sodium sulphate + water

Ionic equation:2Na+(aq)+2OH-(aq)+2H+ (aq)+SO4-(aq) � 2Na+(aq)+SO4-(aq)+2H2O(l)

2OH-(aq) +2H+ (aq) �2H2O(l)

Limitations/Improvements

There was not a very large time span in order to do more experiments, thus only a small amount of results were obtained. However, had there been more time, more data could have been obtained hence the results would have been more valid.