Method
- Wash weighing boat with distilled water and dry
- Weigh 2.65g sodium carbonate
- Put the sodium carbonate into a beaker. Pour distilled water into beaker and stir with glass rod. Wash the weighing boat several times over the beaker with distilled water to ensure all of the sodium carbonate has been transferred.
- Now pour the sodium carbonate into the volumetric flask using a funnel. Rinse the beaker out several times with the distilled water and pour into the volumetric flask. Rinse the glass rod over the volumetric flask.
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Add distilled water to the volumetric flask until the aqueous sodium carbonate is just below the 250cm3 line, shake to make sure all of the sodium carbonate is dissolved and then use a pipette (once rinsed with distilled water) to make up to line (bottom of the meniscus).
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Using the 25cm3 pipette put 25cm3 of sodium carbonate into the conical flask and add three drops of methyl orange indicator. Put to one side.
- Rinse the 50cm3 burette with distilled water. Let it rinse through. Do the same using sulphuric acid and repeat two times.
- Now fill the burette with sulphuric acid. Let acid rinse through to the end and then refill.
- Place the burette into a clamp stand. Put the conical flask under the burette. Let the sulphuric acid pour through until the sodium carbonate changes colour to a light red. When this happens note down this rough titration result.
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Empty the contents of the conical flask and rinse out with distilled water. Put 25cm3 of sodium carbonate into the conical flask using the pipette.
- If there is enough sulphuric acid left in the burette then there is no need to refill, other wise top it up.
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Let the sulphuric acid run through and swirl flask until you get within a few cm3 within the rough titration. Now slowly let the sulphuric acid drop into the sodium carbonate until it changes colour.
- Once it has changed colour, swirl it around and leave to stand for 10 seconds. If the red colour has gone add more sulphuric acid to the conical flask until the red colour stays.
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Once it has changed colour repeat the process until you have three repeat titres within 0.1cm3 of each other.
I think that my method that I have devised is likely to provide precise and reliable results because it provides the exact values of all the solutions that are needed. The equipment that will be used will also be quite accurate as the intervals between each reading will be quite small. This means that the percentage error will be decreased. It should produce reliable results as the experiment has to be repeated until there are three results that are close to each other. I will wash all of the necessary equipment with distilled water to ensure no residue remains on/in the equipment. I will also rinse all of the necessary equipment with distilled water to ensure that no sodium carbonate remained in the weighing boat and beaker etc. To make sure that the acid’s concentration will not decrease I will wash the burette several times with the same molar acid.
Risk Assessment
Results
Weight of sodium carbonate = 2.65g
Amount of sodium carbonate dissolved in distilled water used per titre = 25cm3
I am taking the readings 2,3 and 4 to work out the average titre, as these are the three results that are within 0.1 of each other. The average titre and volume of the sulphuric acid is therefore 24.88 cm3.
Working Out The Concentration
Using my results I can now put all the necessary components into the equation to find the concentration of sulphuric acid within the acid rain.
Na2CO3+H2SO4 Na2SO4+H2O+CO2
Mole Ratio === =
The concentration of the acid rain is therefore equal to:
The concentration of acid within the acid rain is equal to 0.100moldm-3.
The method I took to come to this was:
- By looking at the left hand-side of the equation I took the mole ratio.
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I then put the mole ration equal to the volume of Na2CO3 multiplied by the concentration of it over the volume and concentration of the sulphuric acid.
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The next step I took was to turn the volumes from cm3 to dm3 by dividing by 1000.
- I then multiplied the top two figures together.
- As the concentration is what I am trying to find I cross-multiplied to get the concentration on the other side of the equation.
- I then divided the top by the bottom to come up with the overall concentration.
Evaluation
When looking at my results the obvious anomaly is the first proper titration. This could be because of many things such as inaccurate measuring. I may have put too little sodium carbonate into the conical flask. I could have also added too much methyl orange indicator, which would have caused the sodium carbonate to dilute further, which would result in an unreliable result.
When looking at the other three readings/titres they are all within 0.1 of one another. This shows that these results should be quite accurate as three readings that are very close to each other is a good indication of what the actual reading should be. The first titre was the hardest to judge whether or not it was pink. This is because for the remaining titres I had a solution to compare the rest of them to so that I could judge whether or not the solution had turned pink.
Errors
Mass: 2.64±0.005g, therefore the percentage error is
Pipette: 25±0.04cm3, therefore the percentage error is
Volumetric Flask: 250±0.3 cm3, therefore the percentage error is
Burette: 24.88±(0.05x2)cm3. The reason that the error is multiplied by two is because to readings are being made, the initial and end readings. This means that the percentage error is doubled so the percentage error is
This means that the total percentage error could be ±1.300%. This means the maximum the result could be is 25.203 cm3 and the minimum is 24.557cm3. The percentage error is quite small meaning that I would consider my result to be quite accurate and reliable. It is unlikely to be the maximum or minimum percentage error, as this would have meant that I would have had to make the largest error possible.
It was important to calculate these errors in order to see what the result could have actually been.
