Preparation of Standard solution and Standardization of Hydrochloric acid
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Experiment 1 Preparation of Standard solution and Standardization of Hydrochloric acid Date: 13-09-2010 Objective The objective of carrying out this experiment is to determine the concentration of hydrochloric acid (HCl) by using sodium carbonate (Na2CO3) as the primary standard in volumetric analysis. Procedure 1. All the apparatus are thoroughly washed by de-ionized water before the experiment. 2. About 1.3 g of anhydrous sodium carbonate (Na2CO3) was accurately weighted out using the method of "weighing by difference". 3. The weighed carbonate was transferred to a beaker and about 100 cm3 of de-ionized water added to dissolve it with stirring of glass rod. 4. After dissolving, the solution was transferred to a 250.00 cm3 volumetric flask. 5. The solution was then made up the mark on the neck by adding de-ionized water (add last few drops with dropper.) 6. Pipette and burette are rinsed by the solution to be contained respectively. 7. 25.00 cm3 of sodium carbonate solution was transferred to a clean conical flask using pipette and pipette filler. 8. Two drops of methyl orange indicator were then added to the sodium carbonate solution. 9. 50cm3 of hydrochloric acid are added in to the empty burette. 10. The filled burette is checked without any air bubbles at the jet.
=0.161717143 ~0.162M ?The molarity of given hydrochloric acid is 0.162M 3. Is it necessary to rinse the pipette with the standard sodium carbonate? Explain. Before titration, pipette should be washed with distilled or de-ionized water and then with the solution to be contained (Na2CO3 (aq)). After washing with distilled or de-ionized water ,there maybe water or impurities remained in the pipette. Any water or impurities remained inside the pipette , will dilute the standard sodium carbonate to be contained. In other words , the number of mole of Na2CO3 will be lowered and the Na2CO3 (aq) will be no longer standard. Thus, the molarity of the given HCL(aq) calculated will be inaccurate due to the titration with contaminated Na2CO3(aq). Therefore, pipette should also be rinsed by standard sodium carbonate before transferring the solution during the actual titration. By doing this step, impurities and water remained can be washed away and the number of mole of Na2CO3 in the pipette will be in accordance with the calculated data. 4. Suggest one more method other than using acid-base indicator to detect the end-point of an acid-alkali titration. Data logger with temperature sensor can also be used to detect the end-point of an acid-alkali titration.
Although the end point is reasonably close to the equivalence point , there is still minor difference in volume. Thus, the volume of HCL(aq) added is not exactly the actual volume required for completely neutralizing Na2CO3 (aq). Last but not least, solution may be last due to too vigorous swirl . This can end in liquid splashing from the conical flask before the end point had been reached. Conclusion To conclude, the molarity of the given hydrochloric acid is tested and calculated to be 0.162M. Throughout the titration, it should be noted that chemists should find a correct and suitable chemicals to make primary standard solution. Moreover, it is necessary to rinse the pipette with the solution to be contained or transferred. Furthermore, chemists can use other methods ,such as using data logger with temperature sensor ,to detect the end-point of acid-alkali titration. Furthermore, chemists should aware of the potential errors may be made, in order to decide appropriate measures to reduce the error. By implementing the measures above, the results of titration can be more accurately obtained. Reference Yahoo!Mini http://www.titrations.info/ http://en.wikipedia.org/wiki/Titration http://hk.knowledge.yahoo.com/question/question?qid=7010032200973 http://en.wikipedia.org/wiki/Standard_solution http://en.wikipedia.org/wiki/Primary_standard http://www.creative-chemistry.org.uk/alevel/module1/documents/N-ch1-49.pdf http://en.wikipedia.org/wiki/Data_logger HKCEE Chemistry Notes Section IV by Ms Sin W L F.6 Chemistry Notes Section I by Ms Sin W L End ?? ?? ?? ?? F.6 Chemistry TAS/Experiment 1/P.1(8) 1
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