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Chemistry Peka: Titration (Special Edition)

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Author Topic: Chemistry Peka: Titration (Special Edition)  (Read 2809 times)
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« on: October 04, 2009, 08:51:13 am »

This is the example of Peka Chemistry that I made myself. Hope you all find it useful.

To determine the end point during the neutralization of hydrochloric acid, HCl with sodium hydroxide, NaOH solution using titration method.

25.0 cm3 pipette, burette, 250 cm3 conical flask, retort stand and clamp, white tile.

Hydrochloric acid, HCl, sodium hydroxide, NaOH solution, phenolphthalein

1. A clean burette was rinsed with a small amount of hydrochloric acid, HCl. The burette was clamped on a retort stand.
2. The burette was filled with hydrochloric acid, HCl. The meniscus level of the acid was adjusted to a reading at ‘0’ or slightly below the ‘0’ mark.
3. The initial burette reading was recorded.
4. 25.0 cm³ of sodium hydroxide solution, NaOH was pipetted into a conical flask.
5. Two drops of phenolphthalein were added to the sodium hydroxide, NaOH and the solution was shaken well. The colour of the solution was observed.
6. The conical flask with its content was placed below the burette. A piece of white tile was placed below the conical flask.
7. The hydrochloric acid, HCl was added carefully and slowly from the burette into the conical flask. The conical flask was swirled throughout the process of titration.
8. When the colour of the mixture turned paler, the hydrochloric acid, HCl was added a drop at a time when swirling the flask. The change of the mixture was observed.
9. The addition of hydrochloric acid, HCl was stopped as soon as the solution in the conical flask turned colourless.
10. The final burette reading was recorded.
11. Steps 1 to 10 were repeated again. The reading were tabulated.

Data and Observation :
Titration set   1   2
Final Burette Reading (cm3)   27   26.5
Initial Burette Reading (cm3)   48   48
Volume of hydrochloric acid, HCl needed (cm3)   21   21.5

Discussion :
1.   (a) The average volume of hydrochloric acid, HCl needed to neutralize 25.0cm3 of sodium hydroxide, NaOH solution is (depend on your result)

(b) The equation for reaction between hydrochloric acid, HCl and sodium hydroxide, NaOH solution is HCl + NaOH → NaCl + H2O

(c) The molarity of the dilute sodium hydroxide, NaOH solution is (depend on your result)

2.   (a) The end point of the titration is the point which a drop of acid added to the mixture in the conical flask will change the indicator’s colour from pink to colourless.

        (b) An alternative method to determine the end point of titration is by using a Computer Interface.

3.   Explanation of the following :
(a)   The burette has to be rinsed with a little hydrochloric acid, HCl before filling it up with acid.
→ To remove the water on the interior surface of the burette.
(b)   There must be no bubble of air trapped in the jet of the burette
→ To ensure the accuracy of the reading.
(c)   Burette readings are taken with eye at the same level as the meniscus.
→ To ensure that parallax error will not occur
(d)   Do not rinse the conical flask with sodium hydroxide, NaOH solution.
→ To ensure that the volume of the sodium hydroxide, NaOH solution in the conical flask is  exactly 25.0 cm3.
4.   The function of the white tile is to enable the change in colour in the conical flask to be seen clearly.

Conclusion :
The end point of neutralization between an acid and an alkali can be determined by titration method. The concentration of sodium hydroxide, NaOH is (depend on your result)
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