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# Calculating concentration of Calcium Hydoxide.

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Introduction

In order to find the concentration of calcium hydroxide solution I would carry out a titration. Titration is an example of volumetric analysis. Titration is a technique used to find the concentration of an unknown solution. Using volumetric analysis I can find the concentration of calcium hydroxide if the concentration of the acid is known. Calcium Hydroxide (Ca(OH)2) is formed when Calcium Oxide reacts with water. This reaction is exothermic and the product is slightly alkali. CaO(s) + H2O(l) Ca2+(aq) + 2OH-(aq) Calcium Hydroxide solution is called lime water. Lime water is formed when calcium carbonate(CaCO3(s)) is heated to form calcium oxide or quick lime (CaO(s)) and carbon dioxide (CO2(g)). Which is then reacted with water to form calcium hydroxide or slaked lime (Ca(OH)2(s)), this is then dissolved in water to form an aqueous solution of lime water (Ca(OH)2(aq)). I will write the symbol equation for this reaction below: CaCO3 HEAT CaO(s) + CO2(g) CaO(s) + H2O(l) Ca(OH)2(s) Ca(OH)2(s) + H2O(l) Ca(OH)2(aq) Lime water gives a milky white precipitate when reacted with carbon dioxide: Ca(OH)2(aq) + CO2(g) CaCO3(s) ...read more.

Middle

The enthalpy of neutralisation is approx 58Kjmol-1. Apparatus The apparatus for a titration will include: * Burette * 25cm3 graduated pipette * Pipette filler * Measuring cylinder * Distilled water * Indicator (phenolphthalein) * Hydrochloric acid * 250cm3 of limewater In the titration I would expect the titre to be about 25cm3. 25cm3 solution of Ca(OH)2 will contain approx (25 � 250) x 1 = 0.1g Mr of Ca(OH)2 = 40.1 + 16 + 16 + 1 + 1 = 74.1g Moles of Ca(OH)2 = mass � Mr = 0.1 � 74.1 = 1.35 x 10-3 From the equation, 2 moles of HCl will react with 1 mole of Ca(OH)2. Therefore moles of HCl = 2 x (1.35 x 10-3) = 2.7 x 10-3 Concentration of HCl is 2 mol dm-3 Moles = (volume � 1000) x concentration Volume = (moles x 1000) � concentration = (2.7 x 10-3 x 1000) � 2 = 2.7 � 2 = 1.35 cm3 This shows that 1.35cm3 of 2 moles of HCl is needed. ...read more.

Conclusion

Therefore it is wise that gloves should be worn and when it is not in use it should be keep away in storage. The indicators used in acid-base titrations are weak acids or weak bases which can dissociate in aqueous solution. Imagine a weak acid, HIn. HIn(aq) H+(aq) + In-(aq) (colourless) (red) If HIn and In- are different colours, then HIn will act as an indicator. In a solution with high concentration of H+ (and acid) the equilibrium will be forced to the left. As predicted by Le Chatelier's principle, almost all the indicator will exist as HIn and the solution will be colourless. In an alkaline solution where the concentration of OH- is high, H+ ions will be removed as water (H2O). HIn H+(aq) + In-(aq) H+(aq) + OH-(aq) H2O(l) Le Chateliers principle predicts that the equilibrium will move to the right and most of the indicator will exist as In-(red). Structure of Phenolphthalein Another indicator suitable for strong acid/weak base titration is methyl orange. This indicator is red in acidic solutions, and yellow in alkaline solutions. ...read more.

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