Method
As always when doing an experiment safety is one of the key elements, especially when dealing with acids. It is very important to wear eye protection when working with acid as they can seriously damage the eyes. If hair is long then it is sensible to tie the hair back to avoid getting in the way when proceeding with the experiment. A fume cupboard can be used because of the concentration of the acids; it can be harmful as it is toxic. There must be good ventilation. If any spills occur while diluting the concentrated it must be dried up quickly. There must be immediate access to running water. Also add acid to water, never add water to acid. Never inhale the acid or blow into the pipette.
Before I can continue with the experiment I must dilute my acid. To insure that I dilute it precisely I must use a volumetric flak and pipette. I measure out 475cm3 of Distilled water and place it into the volumetric Flask then pipette 25cm3 of hydrochloric acid and pour it into the volumetric flask to make up the difference. I will also perform the experiment several times so I know that my results are dependable.
Diagram
- Using the funnel, rinse the diluted acid into a burette.
- Using the pipette filler, rinse the pipette with 25cm3 of Limewater solution. Place into the conical flask, place under burette on a white tile.
- Add a few drops of indicator 2-4 (Methyl Orange)
- Run Hydrochloric from the burette into the Limewater in the conical flask. With swirling until it turns a neutral colour.
- Refill the burette with hydrochloric acid and again record the initial burette-reading make a note of the volume of acid used.
- Using the pipette transfer 25cm3 of the Limewater solution to another clean conical flask. Add a few drops of indicator.
- Repeat steps 4,5 and 6.
- Empty the burette and wash it carefully immediately after the titration.
Analysis
Table of Results from the experiment
The mean value of the titration used is 13cm3
Because 12.5 +13 +13.5 = 39 39/3 =13
Ca(OH) 2 + 2HCL ➔ 2H2O + CACL2
25cm3 13cm3
0.1mol/dm3
Moles = concentration x Volume
Moles of HCL = 13/1000 x 0.1 moldm3
Moles of Limewater 0.0013/2
= 0.00065mol
Concentration = 0.00065/0.025
= 0.026mol/dm3
Mass of Ca(OH) needs in gram = 40+(16+1) x2 = 74 g
Therefore 74 x 0.026 = 1.924g/dm3
Conclusion:
I was able to establish the concentration of the Limewater I believe it is 1.924g/dm3. I believe my results are accurate as I followed the safety code and measured out the hydrochloric acid and the Limewater exactly using the correct equipment, which was available. Looking at the results they are quite close to each other, there isn’t really a big difference for example it was like 12.5cm to 13cm.
Evaluation:
The task set was to determine the concentration of Limewater. My experiment went according to plan as the results I gained there was consistency and in some ways proves that my experiment is reliable as well as accurate. But still errors are still likely occur when measuring the amount of acid that has gone down and when the colour changes occur
There were few changes I had to make due to the lack of equipment available. I needed a 500cm volumetric flask to do my experiment but there were only 250cm volumetric flask left. So I used the 250cm one, so that meant that I added 237.5 cm of distilled water and made up the difference with the hydrochloric by 12.5 cm. At the end of the experiment there was still some diluted acid left so maybe I should have diluted it by 100 instead of 250. I feel that I should have stopped titration as soon as I saw climes of the neutral colour as I waited for it to turn the full colour.
If I had to do this experiment again I would prepare about four conical flask to reduce time because each time I did titration I had to stop and wash the conical flask with distilled water so there wasn’t any traces of Limewater in the conical flask. I would also use a ph meter so it would be more accurate.
