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Plan. In this experiment I intend to discover the exact concentration of an unknown limewater solution using the method of titration.

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Introduction

F.CLOUGH ASSESSED PRACTICAL- To determine the concentration of a limewater solution: In this experiment I intend to discover the exact concentration of an unknown limewater solution using the method of titration. In order to produce accurate and reliable results it is necessary to minimise errors occurring in the procedure. In order to achieve this it is necessary to stringently abide to the instructions detailed in this plan: EQUIPMENT: * 250 cm3 limewater solution (Ca(OH)2) (approx. 1g dm-3) * Hydrochloric acid (exactly 2.00 mol dm-3) - Acid solution of known concentration that is to be used to find the concentration of the basic solution. * Distilled water- For dilution of hydrochloric acid to a reasonable level, also to clean out burette and pipette to avoid any anomalous values in results caused by impurities in the solution. * Methyl orange indicator- Acid-base indicator that undergoes a change in colour when the end-point of a titration is reached. * Burette- Graduated vessel -with tap- to accurately determine the amount of hydrochloric acid that is needed to reach the end point of the titration, when the limewater solution has been neutralised. ...read more.

Middle

(The reason for having double the concentration is that in the reaction between calcium hydroxide and hydrochloric acid, two molecules of HCl are used up for each molecule of Ca(OH)2. This means that twice the amount of molecules of HCl is needed in the reaction.) The reason for not choosing 0.02 mol dm-3 is that it would take too much hydrochloric acid to reach the end point of the titration at this concentration and it would also be harder to dilute, resulting in increased errors in the experiment and therefore less accurate results, so 0.2 mol dm-3 was chosen as more suitable. It is necessary to dilute the provided 2.00 mol dm-3 using a 10 cm3 pipette and a 100 cm3 volumetric flask. Prior to diluting the hydrochloric acid it is necessary to rinse the flask with distilled water. 10 cm3 of the HCl is transferred to the volumetric flask, the flask is then filled to the top with distilled water, this solution must then be shaken vigorously to produce a 0.2 mol dm-3 solution. ...read more.

Conclusion

should be added to the limewater until it is an orange colour. Once all is in place and the reading on the burette has been noted down, the titration can begin. The tap is opened to add hydrochloric acid until a distinct colour change has occurred (the previously orange limewater should turn colourless), stirring constantly throughout. As soon as the colour has changed the tap is closed and the final reading is taken from the burette (ensuring that it is from the bottom of the meniscus). At least 3 readings should be taken, the first being a rough reading and less care is needed when adding the sodium hydroxide, the other two need more precision so they should be carried out practically drop by drop until the colour changes. The first result tends to be discarded unless it is very similar to the other results. An average is taken of the two (or three) results. My results shall be recorded in the following tabulated form: Reading 1 (rough) 2 3 4 Quantity of HCl needed to neutralise the limewater solution (cm3) ...read more.

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