Method:
Preparing my stock solution:
- Weigh the empty bottle
- Leave the bottle on scale and make sure the scale reads 00.00
- Using a spatula weigh 6.1g of sodium carbonate in the weighing bottle
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Put about 100cm3 of distilled water into a 250cm3 beaker.
- Carefully pour the sodium carbonate from the weighing bottle into the beaker.
- Wash out the bottle with distilled water 3 times to ensure all the sodium carbonate comes out of the bottle.
- Use the mixing rod to break all the crystals.
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Add more distilled water if necessary. (remember there should be no more than 250cm3 of water in the beaker at the end)
- Once all the crystals of sodium carbonate have been dissolved, wash the rod in the beaker with distilled water three times.
- Then pour the solution in the beaker into the conical flask.
- Wash the beaker out three times with distilled water into the conical flask to ensure all the solution goes into the flask. (this is to ensure precision)
- Carry on adding distilled water to the flask until it reaches the meniscus level.
- Once it has reached the meniscus level call the teacher to check u have done everything correctly.
- Put the top onto the flask and shake it to ensure the solution is all well mixed.
- Finally pour the solution into a beaker again, and your stock solution is now ready.
Here is the procedure by which the titration will be carried out.
- Set-up the stand and the burette, held firmly in position by the clamps.
- Fill the burette using a filter funnel with 25cm of sulphuric acid. Air bubbles should be avoided.
- Read off the zero mark at eye level to ensure that the bottom of the meniscus is on the mark.
- Now by using the pipette transfer to the graduation mark on the stem with the sodium carbonate solution and carefully add this to the conical flask. DO NOT blow out the last drops.
- Use a pipette and a pipette filler to transfer 10.0 cm3 of the acid rain sample to a 100 cm3 conical flask.
- Add 3 drops of Methyl orange indicator.
- Fill burette with 0.01 mol dm-3 sodium hydroxide solution.
- Make sure the burette jet is also full of solution.
- Record the volume reading in the burette before starting the titration.
- Add sodium hydroxide solution in small volumes to the acid rain solution in the conical flask.
- Gently swirl the flask after each addition.
- The Methyl orange indicator should turn from a orange to a yellow colour.
- Run in the small volumes of sodium hydroxide solution until there is a colour change from yellow to orange colour in the titration mixture.
- This is the end point.
- Record the final burette reading.
- Now calculate the volume of hydroxide solution that has been used.
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The 1st attempt that is done would be a rough titration.
- From this rough attempt I should now have an idea of what the end point is.
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After this rough titration I will do several more titrations until I record three volumes that agree to within 0.1 cm3.
The results that I get are to be recorded into a table like the one shown below:
Average Titre = ___________cm3
Analysis:
After I had done my Titration, the results I got have been recorded in the table below:
The three sets of underlined results are those that are in 0.1cm3 of each other.
Now in order for me to work out my average titre I will have to add 3 or my Final burette readings and divide them by 3.
(30.15+30.15+30.10) = 30.13cm-3
3
Average Titre = _ 30.13 cm-3
The equation that I have written below shows what happens when the solution of sodium carbonate reacts with the sulphuric acid.
H2SO4 (aq) + Na2CO3 (aq) à Na2SO4 (aq) + CO2 (g) + H2O(l)
Now I am going to work out the concentration of sodium carbonate used.
In order for me to work out this I will have to use the equation below:
Concentration= Number of moles
Volume
Number of moles= Mass
RFM
=2.65
106
= 0.025 moles
So if the concentration = Number of moles
Volume
= 0.025 / 0.250
= 0.1 moldm-3
If I want to find out the number of miles in the actual amount that is being titrated each time I must divide the number of moles in the conical flask by 10, this is because 250 divided by 25 = 10. So the number of moles that have been used in the standard solution are 0.0025 moles.
Now by looking back at the equation I can see that 1 mole of sodium carbonate reacts with one mole of sulphuric acid. So in my experiment of titration I can see that 0.0025 moles of sodium carbonate react with 0.0025 moles of sulphuric acid. It has a ration of 1:1.
Therefore now that I know the average titre and the number of moles being used I can work out the concentration of acid.
To work out the concentration I have to use the equation below, which is:
Concentration = Number of Moles / Volume
= 0.0025 / 0.03013 dm3
= 0.08297 moldm-3
= 0.083 (2.d.p)
The concentration of the acid is 0.083 moldm-3.
Conclusion:
By looking at the results that I have gained after doing this titration I can see that the concentration of the acid is 0.083 moldm-3. however even though this result that I have gained may not be entirely precise or correct, I can say that it is a reasonable result because at the beginning of this investigation I was told that the acid is somewhere in between 0.05 and 0.15 moldm3. This shows that the results I have gained are reasonable as they are in the expected range.
Evaluation:
During the course of this investigation I may have caused many minor errors, which have obviously affected my final results. The reason for the errors is that the measuring equipment that I have used is only designed to give a certain degree of accuracy and cannot always be precise.
Below are my percentage errors:
As u can see below that my percentage errors were rather low, this means that the results I have gained for my titration are rather precise. Also I didn’t get any anomalous results, this suggests that the titration I had carried out was carried out fairly accurately. The equipment that I have used is reasonably accurate equipment, it is necessary to have accurate equipment to get accurate results when an investigation such as titration is carried out.
Percentage errors
Balance = 0.005 x 100 / 2.65
= 0.189% (3sf)
Burette = 0.05 x 100 / 30.13
= 0.165% (3sf)
Pipette = 0.240%
Flask = 0.080%
To make sure all the weighed sodium carbonate entered the solution, I rinsed the funnel, beaker and glass rod each three times with distilled water and added it to the volumetric flask. This was to ensure a great deal of accuracy with the concentration of my alkaline solution, which is crucial in determining the concentration of the acid. All the reading that I took from the burette, pipette and the conical flasks were taken using the bottom of the meniscus.
As sulphuric acid is a very strong acid and sodium carbonate is weak alkali, I realised that methyl orange was the best indicator to use. I feel it was best to have the acid placed in the burette rather than it in the conical flask, because it’s easier to note the colour change from yellow to orange, than orange to yellow.
I know that the errors that may have occurred during the experiment were minor and did not have a great impact on my final result, however I still feel that the main source of my error in carrying out the titration was where I had to distinguish where the indicator had changes colour. This is the reason for why I had to estimate an end point between the beginning and end point of the colour change. I used this method throughout all 3 of my titrations.
If I was to ever do this experiment again I would make sure that I used a pH meter to distinguish the neutralization point. Even though by doing this it would not have a great impact on my titre, it will however make the investigation much more reliable and not subject to the choice of individual colour change. Also if I had more time to do this experiment I would do more titres rather than just 1 rough titre and three others. I would do several titres in order to compare them with one another.
