Slaked lime dissolved in water is called limewater.
Quicklime + Water -> Slaked lime
CaO(s) + H2O(l) -> Ca(OH)2(s)
Calcium oxide reacts violently with water to produce calcium hydroxide (slaked lime). Addition of further water to Calcium hydroxide produces the saturated aqueous solution known as Limewater. In the experiment it is necessary to react the Hydrochloric acid with the Limewater in order to establish the concentration of the limewater.
Acid + Metal Hydroxide -> Salt + Water
The balanced equation that takes place is:
Limewater + Hydrochloric acid -> Calcium chloride + Water + Hydrogen
Ca(OH)2(aq) + 2HCl ? CaCl2 + 2H2O
In order for the experiment to be accurate and reliable it will be necessary to dilute the Hydrochloric acid significantly. It is in my belief that a concentration of 0.1mol/dm3 would enable me to achieve reliable results. This would require a dilution factor of twenty. I will be making 500 cm3 of dilute hydrochloric acid. I will also be using 25cm3 of Limewater.
In order to reduce errors it is necessary to choose accurate and reliable equipment. That is why I have chosen the pipette, volumetric flask and burette. All of these instruments have an accuracy of ±0.05cm3, which is suitable for my experiment and should produce accurate and reliable results. In making my choice of indicator I also had to be very careful. The Limewater used will be a relatively weak base so it will be appropriate to use methyl orange as it has an end point on the ph scale between 8-5. Whereas phenolphthalein indicator has an end point much higher up in the ph scale. So if I were to use the phenolphthalein indicator then the end point (colour change) would be reached before the equivalence point (when the chemicals, acid-base break up).
Implementing
Safety is very important and it is necessary to follow safety procedures. It is important to wear eye protection when working with any acid. Also long hair should be tied back. A lab coat should be worn at all times. Also as the chemicals used are corrosive it is important to take extra care while working around them.
In order to start with the experiment it is required of me to dilute the HCl. An accurate way of doing this is to use a volumetric flask and pipette. I want to dilute the acid to 0.1 moles, so I pipette 25.0cm3 of HCl from the original bottle and place it in the 500cm3 volumetric flask. Then I add 475cm3 of distilled water to the same volumetric flask, I measure the amount of water by looking at the graduated mark on the flask and fill until the 500cm3 mark.
Once I have obtained the correct concentration of Hydrochloric acid I can precede to the rest of the experiment. First I must set up the apparatus as I have indicated in my diagram. I will be using 25.0cm3 of limewater and I will transfer it into the conical flask using a 25.0cm3 pipette. It is also important to add the indicator into the conical flask so that the neutralisation point can be obtained, where three drops of methyl orange should be appropriate. When the indicator is added the colour of the solution is light, clear, orange and this should turn to pink by the end of the titration. In order to obtain consistent and reliable results it is necessary to repeat the experiment 3 times at a minimum and if the results were not in 0.1 of each other then further experiments would be needed. 0.1 is the figure that I have used as it is the accuracy of the burette. After this it the results must be noted in a table complete with the correct units. Using these results we first apply this formula
Number of moles= concentration*volume(dm3)
to the Hcl as we know its amount and concentration so can work out its number of moles. We then look back at the balanced equation and see the reaction ratio. In this case it is 2 moles of Hcl to 1mole of Ca(OH)2. So we times this number by 2 and we have the number of moles of limewater.
