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Acid-base titration. Objective To determine the concentration of sulphuric acid (H2SO4) using sodium carbonate (Na2CO3) as the primary standard in volumetric analysis.

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Introduction

Tsuen Wan Public Ho Chuen Yiu Memorial College Form 6 Chemistry Practical Experiment 1: ACIS-BASE TITRATION Date of experiment: 24-9-2010 Objective To determine the concentration of sulphuric acid (H2SO4) using sodium carbonate (Na2CO3) as the primary standard in volumetric analysis. Introduction A major part of chemistry is being able to analyze compounds to see how much of a given chemical they contain. One method that is often used is volumetric analysis. We use a known solution and react it with a solution of the chemical being studied. The typical way of doing this is in a titration. The essential procedure consists of running a solution from a burette into a known volume of another solution as measured out by a pipette in a conical flask, until the two solutions have just reacted completely with each other. This is the equivalence point of the reaction. This point is often marked by the change in colour of a chemical called an indicator. The solution in the burette is called the titrant while the volume of it used to reach the end point is called the titre. Usually, the titration is carried out by neutralization: Acid+ Base Salt + H2O OR Acid+ Carbonate Salt + CO2 + H2O Chemicals used Anhydrous sodium carbonate About 1.3 g Sulphuric acid A big bottle shared Methyl orange indicator Several drops per time Apparatus Weighing bottle x 1 Electronic balance x 1 100cm3 beaker x 2 Glass rod x 1 250.0 cm3 volumetric flask x 1 ...read more.

Middle

The reading should be accurate to 2 decimal places. 14. The tip of burette was inserted into the mouth of conical flask containing the standard sodium carbonate. Titration was started by opening the stopcock of the burette to allow sulphuric acid to drain into the flask. During the process of titration, the conical flask was swirled continuously to mix the solutions. When the solution in the conical flask just changed from yellow to orange, the stopcock of the burette was closed immediately. 15. The final burette reading was recorded in the table provided. This was a trial titration to estimate the volume of hydrochloric acid required. The volume of sulphuric acid added in titration was calculated. 16. The given sulphuric acid was added to the burette through a filter funnel if the volume remained was not enough to carry out another titration. 17. Steps 9-16 were repeated to obtain 3 more sets of consistent results (difference of results within 0.10 cm3). However, draining of sulphuric acid was stopped at about 3 cm3 less than the estimated value. Then sulphuric acid was added drop by drop until the reaction mixture in conical flask just changed from yellow to orange. Results Observation Change of solution from yellow to orange Data Material Mass (g) Mass of weighing bottle + sodium carbonate powder 5.99 Mass of weighing bottle 4.69 Mass of sodium carbonate 1.30 1st (Trial) ...read more.

Conclusion

Other errors: 1. When I was making up the solution, the sodium carbonate powder may not dissolve well and the solution may not mix well. 2. Before the titration, I need to use distilled water to wash the pipette and burette. Then use chemical that need to contain in the pipette and burette to wash them. 3. During these processes, some distilled water may leave on the surface of them. 4. After each titration, I need to wash the conical flask again. Therefore, some chemicals may leave on the surface of the conical flask. 5. When I was pouring the dissolved sodium carbonate into the volumetric flask, I may carelessly pipetted 25 cm3 of it instead of pouring the whole beaker of solution into the volumetric flask. Hence, the no of moles of Na2CO3 was apparently reduced and the molarity of sulphuric acid was underestimated. Those cases I mention above may affect the result of the experiment. Therefore, my result (the concentration of sulphuric acid and the relative molecular mass of sodium carbonate) may not be very accurate. 5. Precautions * Remove the funnel above the burette to prevent an 'air lock' during titration * The tip of the burette should be brought closer to the solution in the conical flask, to prevent excessive splashing of un-neutralized droplets all over the sides of the conical flask. 6. Rinsing the conical flasks provided with distilled water does not spoil the titration because the number of moles of solute remains unchanged after water is added. ~END OF LAB REPORT~ ...read more.

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