In the flask I have used 25.0cm3 of limewater and a few drops of methyl orange. Obtained by using a pipette. By adding the drops of methyl orange the neutralisation point should be acquired. The solution should turn a light orange and proceed to pink at the end of the experiment.
By slowly adding the acid into the limewater the point where complete reaction occurs is when the indicator changes colour. This is known as the equivalence point. This experiment is then repeated several times in order to gain the necessary reliable results.
My results are as follows:
Average titration = 10.9+11.2+11.1+11.1+10.5= 54.8 54.8÷5=10.96
Balanced equations
In order to achieve limewater we dissolve slaked lime in water to get a solution of calcium hydroxide (Ca (OH) (aq)).
Quicklime + water → Slaked lime
CaO(s)+H20(I) → Ca(OH)2(s)
In this reaction it shows how the calcium oxide reacts with water to produce calcium hydroxide. After adding more water to calcium hydroxide it produces the saturated aqueous solution known as Limewater.
In the experiment limewater reacts with hydrochloric acid, to make the concentration of the limewater.
Limewater + Hydrochloric acid → Calcium chloride + water + Hydrogen
Ca(OH)2(aq)+2HCL → CaCl2+ 2H20
Calculations
Number of moles of HCL
Number of moles = volume of solution x molarity
1dm3 = 10x10x10cm3 = 1000cm3
10.96 ÷ 1000 x 0.125 = 0.00137 = 1.3 x 10 mol
Concentration of limewater in mol dm3
2(Volume of acid cm3) x Molarity of acid = Volume of alkalai (cm3) x Molarity of alkalai
- 1000
2 (10.96cm3 x 0.125) = 25cm3 x mo.Ca(OH)2
1000 1000
= 0.00274
Mol. Ca(OH)2 = 0.00274 x 1000 = 0.1096 mol dm3
25
0.1096 x 74.1(Molarmass) = 8.12gdm3
Evaluation
My practical experiment went quite well and I got a variety of results, which were suitable for the task given. My results show that I got two identical results and one just 1.1cm3 off. Which suggests that I have been accurate and precise during the experiment. By being accurate it came about by specific apparatus I used, which restricted errors. However during the experiment I came across an array of errors and circumstances that could have restricted my results. Some of which include Random and systematic errors. Some of the miscalculations I made consist of: -
- Splashes occurring on the flask during titration
- Chemicals carried over to the next experiment
- Colour change not exact
- Measurements not accurate
- Pipette holding back solution
The first error I found was that when I was carrying out the titration process, fractional splashes were occurring on the sides of the flask while the titration was taking place. This could maybe be avoided next time by lowering the burette to the bottom of the flask so hardly any splashes can occur. The pipette that I used was also holding back some of the solution so not all of the solution was transferred. This problem also occurred when measuring the chemicals because some chemicals were carried over to the next experiment. This could be avoided by drying out the beakers and measuring cylinders or by using separate apparatus. A lot of the errors came from measurements because you rely on the human eye. However the measurements were as accurate as possible. The pipette and burette have an accuracy of approximately ±0.05cm3. This is a lot more accurate compared to that of the burette, which has an accuracy of ±5.00cm3. Knowing this information explains how error through equipment is minimal. Also rely on by the human eye would be the judgement of colour change. It’s very difficult to get the exact same colour at the end point of the indicator with the naked eye. Which is why I have used 0.125mol dm of Hydrochloric acid because it makes the results easier to counter for.
The experiment can be made better by making sure all the above errors are accurate and improved on. Also doing several more titration experiments will give me more results, which would make my average result better and more precise. If there were a bigger quantity of limewater for the titration it would reduce the percentage error. In some laboratories specific computer software can be used. Certain programs hold information on the previous titration and when the second titration matches the previous; the experiment is automatically stopped. This is a very accurate way of judging the colour change and totally rules out human error.
I think my results are reasonably accurate and fair and I have avoided from making any real big experimental errors.