Procedure:
Na2CO3 (aq) + H2SO4 (aq) = Na2SO4 (aq) + H2O (l) + CO2 (l)
They react together in a 1:1 ratio.
I will make up the sodium carbonate solution to a concentration of 0.1 molar. This amount is between 0.05 and 0.15 which is thought to be the concentration of the acid. I will work out how many gram of each element there is in the compound of sodium carbonate.
Moles= volume x concentration
1000
Na x 2 = 45.99
C x 1 = 12.00
O x 3 = 48.00
Total= 105.99
I want to make a 250cm3 of 0.1 mol solution dissolve 105.99 of sodium carbonate in 1dm-3 of distilled water, to make a 0.1 mol solution dissolve 10.599g of sodium carbonate in 1dm-3 of water. I will use 250cm3 because it will be enough to do repeats in the experiment and if any spillages occur I will have some more.
To make 250cm3 of 0.1 ml solution dissolve 10.599/4g sodium carbonate in 250cm3 of water.
So, 10.599/4=2.65g of Na2CO3 in 250cm3 of distilled water.
Before I weigh out the sodium carbonate, I must make sure that the top pan balance is completely clean. I will make sure that the spirit level is even and the top pan balance is set at zero. I will place the weighing bottle onto the top pan balance and zero it. I will use a spatula to accurately measure 2.65g of sodium carbonate. Once I have got the exact amount of sodium carbonate I will need to dissolve it in distilled water. I will empty the contents into a 250cm3 beaker, rinsing down the weighing bottle with distilled water so prevent losing any sodium carbonate. When the sodium carbonate is in the 250cm3 beaker I will dissolve it using a glass rod, ensuring that all the lumps have completely dissolved. Once it has all dissolved, I will rinse the flask with distilled water, to clean from any substances. I will use the flask to transfer the solution to the volumetric flask, and then I will rinse the beaker and funnel to ensure that no sodium carbonate is lost. I will then add the distilled water into the volumetric flask, stopping just below the calibration line, and then I add more distilled water by small drops using a pipette to guarantee that I get to the calibration line exactly. When I know I have got the correct amount I will then place a plain piece of white paper with a thick black line on, this will ensure that I can see the line and the meniscus clearly line up. I will shake the volumetric flask to make sure the solution is completely mixed together.
I will set all of my apparatus and rinse though everything with distilled water before using it, this will reduced contamination from other substances. I will rinse the burette with acid, then using a funnel I will fill up the burette up above the zero mark so then I can run a little of acid through to ensure that the jet is full. By placing a piece of white paper behind it with the line on it like the diagram above, I will be able to record an accurate reading on the burette. Using the graduated pipette, I will measure out 25cm3 of sodium carbonate solution will be transferred to the conical flask, along with five drops of methyl orange indicator. I will then run in the acid from the burette slowly keeping a hand on the tap and swirling the flask at the same time. When the acid comes into contact with the sodium carbonate there will be a pink area in an orange solution.
The acid will need to be added drop by drop as the colour becomes more intense. When the pink colour remains for 30 seconds the reaction is complete. A white tile was placed under the conical flask to make the end point easier to identify.
I will take the reading of the level in the burette as before and record it. This is my rough titration.
I will need to dispose of the solution in the conical flask, rinse it with distilled water and repeat the titration process above until I have at least three readings within 0.1cm3 of each other. I will repeat this experiment so I can get accurate results.
References:
- Hazard Card for sulphuric acid
- Hazard card for sodium carbonate
-
Vogel’s textbook, 5th edition 1984 page numbers 81, 82 and 84.
Results
Analysis
Interpreting and calculating the results:
Na2CO3 Volume 25cm3 = 25 × 10-3dm3
Concentration = moles
Volume
Moles = concentration × volume
= 0.1moledm-3 × 25 × 10-3dm3
= 0.0025 moles
Reacts 1:1 with acid
So concentration = _______x_______
Average titre
I am only going to take the average of the three closest results
Average =25.70+25.70+25.60=25.6 cm3
3
Concentration = 0.1moledm-3× 25 × 10-3dm3 = 0.097
25.6 × 10-3dm3
Concentration = 0.097 mole dm-3
Evaluation
Where the errors could happen:
% error = error x 100
Mass used
Volumetric flask: When a 250cm3 volumetric flask is filled correctly, i.e. the bottom of the meniscus rests on the calibration line; the error is +-0.3cm3.
0.3cm3 x 100
250cm3
=0.12%
Burette: One drop from a burette has a volume of approximately +-0.05cm3. All burette readings should include two decimal places in which the second is either 0 or 5. An error of one drop in a volume of 25.00cm3 gives a percentage error of 0.2% for each reading. After calculating the average titre you should correct the value to one decimal place.
0.05cm3 x 100
25.00cm3
=0.2%
Pipette: When a 25cm3 pipette is used correctly, i.e. it is allowed to drain and retain the last drop; the error is +-0.06cm3
0.06cm3 x 100
25cm3
=0.24%
Top pan balance: +- 0.005g
0.005g x 100
2.65g
=0.19%
Percentage error for glassware = 0.19% + 0.12% + 0.2% + 0.24% = 0.75%
Errors for all the glassware
Error for top pan balance = 0.19%
Error for graduated pipette = 0.24%
Error for conical flask = 0.08%
Error for burette = 0.235%
Total error for titre1 0.555%
This error is most likely to be not very significant as it will be very small difference.
The main sources of error in my experiment were when I had decided when the end point was; for example judging the colour change of the indicator. It could too pink or just under and making sure that I get the same colour for each titration.
I think that my results are reasonably accurate as a few of them are within the 0.1 range, so this gives less error. There is a very small and almost insignificant percentage error for the glassware.
I suppose that the concentration of the sulphuric acid I was given is near to 0.1 as there is a likelihood of a percentage error.
Weighing by difference increased the accurateness of and reliability of my results as the percentage error is fewer than if I had not weighed by difference. I washed the glassware with correct solutions as it washes away any traces of substances as these may change my results. Washing down the side of the flask during the titration made certain that all the acid I had run in was gone. Using a white tile could help me recognize the end point of the reaction. The white piece of paper made the meniscus easier to see and take a reading from. I must use the same amount of orange methyl indicator in each titration done, otherwise it would have been an unfair experiment and it would have affected my overall results.
