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Back Titration

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Chemistry Lab Report Back Titration Introduction In this practical we are going to determine the mass of a sample of a solid base using the back titration technique. The sample used in this experiment was the calcium hydroxide. It was reacted with an excess of hydrochloric acid reagent and then a titration carried out with a titrand of know concentration NaOH. Materials Hydrochloric acid 0.50M Sodium Hydroxide 0.25M Unknown mass of Calcium Hydroxide Pipette 10 ml 0.015 Burette 0.1 BTB Magnetic stirrer Procedure and Calculations At first, 0.05 dm-3 of hydrochloric acid with a concentration of 50M was prepared in a beaker then a sample of unknown mass of calcium hydroxide was added to the acid and a solution was formed. ...read more.


The experiment was repeated three times in order to avoid errors made and in each time the volume of NaOH added was recorded. Raw data table of the titration being made between the NaOH and the solution of HCl and Ca(OH)2 Volume of NaOH added �0.1 The color of the resultant solution Titration 1 0.0054 Greenish Titration 2 0.0055 Greenish Titration 3 0.0059 Greenish The average volume of NaOH is �0.1dm3 Now to determine the mass of the calcium hydroxide we need to know the amount of the hydrochloric acid and hence the amount of the calcium hydroxide The amount of the alkali from the titration is: NaOH = c x V= 0.25 x 0.0056 =0.0014mol The equation of the reaction between the hydrochloric acid and sodium hydroxide is: HCl (aq) ...read more.


mass of Ca(OH)2 is = n x M = 0.0118mol x 74.10g mol-1=0.874g Conclusion and Evaluation The mass of the calcium hydroxide was determined using the back titration and it is 0.874g. Now to compare it with the real mass of the calcium hydroxide sample 0.74g This indicated that there is a big error occurred during the experiment. The problem for this error might be the high concentration of the NaOH because it was used only around 6ml to get the substance green while if we wanted to get the real mass of the Ca(OH)2 then ml 20ml of NaOH should have been added. The experiment was not hard to follow and it was quite easy. To improve our measurements the experiment need to be repeated more times. ...read more.

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