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# Determining the concentration of lime water

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Introduction

Determining the concentration of lime water Introduction Titrations involve adding a known concentration of acid to an unknown concentration of a base. I will be adding Nitric acid (HNO3) in an aqueous state to Calcium Hydroxide (Ca (OH) 2) which will also be an aqueous state. Aim The aim of the practical is to determine the concentration of the Calcium hydroxide that I have been provided with as accurately as possible. I have been provided with a 250 cm� solution of lime water which has been made so that it contains exactly 0.8dm� of Calcium Hydroxide. I have also available some Nitric acid which has a concentration of exactly 1.50 dm-�. The equation of the reaction is shown below. Equation Nitric acid + Calcium Hydroxide calcium nitrate + water 2HNO3 (aq) + Ca (OH) 2 (aq) Ca (NO3)2 (aq) + 2H2O (l) Apparatus I will be using the following apparatus in the titration experiment: * A '200 cm�' volumetric flask * A volumetric pipette (25.0 cm�) * A graduated pipette for the dilution * A burette * 2 small beakers (150 cm�) ...read more.

Middle

Adding hydroxide ions removes the hydrogen ions from the equilibrium, which tips to the right to replace them - turning the indicator pink. Indicator Colour at low pH Transition pH range (approximate) Colour at high pH Methyl orange red 3.1-4.4 yellow Phenolphthalein colourless 8.2-10.0 pink (http://en.wikipedia.org/wiki/PH_indicator ) I will use methyl orange indicator in place of phenolphthalein because methyl orange is more suitable because the reaction between Nitric acid and Calcium Hydroxide is that of a strong acid and a weak base. Methyl orange reaches its end point at the PH between 8-5 and so is good for the titration that I will be performing unlike phenolphthalein which reaches its end point before the reaction ends. * Method * * Method for diluting the Nitric acid * Firstly I will dilute the Nitric acid to reduce the concentration of the acid. I will do this by adding 3.0 cm� of Nitric acid, measured by the graduated pipette (that I would have already rinsed by the Nitric acid) from the container containing the acid to the volumetric flask of the size of 250 ml. ...read more.

Conclusion

* Once there is a definite colour change which should be from a yellow colour to an orange colour, I will close the tap on the burette and record the titre value. * I will follow the method that I have listed above for the rough titre first and then I will repeat the titration four times. * I will make sure that the next time I do my titration again I let the acid down through the burette very slowly and after a couple of drops, I will close the tap on the burette and swirl the conical flask. If there is no colour change then I will allow some more Nitric acid to pass through the burette and I will swirl the conical flask to see if there is any colour change. * I will get the average titre by adding the four real titre values and not the value of the rough titre and dividing the answer by four. * I will present my results in a table, showing all the titre values that I have received and the calculated average titre. ?? ?? ?? ?? Wafia Pervez ...read more.

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