Risk assessment
- Always wear a lab-coat to protect your skin and cloths from harmful substances.
- Wear goggles at all times during an experiments, to protect your eyes from chemicals.
- Make sure that long hair is tied back and that any dangling clothes and jewellery are tucked away or taken off so that it won’t catch a fire, or become a hazard.
- Always behave in a well-mannered way in a laboratory. Running and playing games could be dangerous.
- If your skin has come in contact with chemicals, quickly wash your hands with cold water and soap.
- You should not eat or drink during an experiment, as it could get contaminated.
- Be careful when using sulphuric acid, even though it is not that harmful as it has a low concentration, make sure that it does not come in contact with your skin, as it could cause burns and irritation to the eyes. Make sure you clean up any spillages. If it has come in contact with skin or eyes, run your skin under cold water and wash eyes with water carefully.
- Methyl orange should also be used with care. It is not very harmful but could stain your clothes and skin. Again avoid contact with eyes and skin.
- Sodium carbonate is not dangerous as it is very dilute, but make sure that it does not come in contact with your skin and eyes for safety reasons. Clean up any spillages.
- Make sure that you clean up any spillages due to washing the glassware with distilled water or using other chemicals so that floors are not slippery, for the safety of other people.
- Keep the laboratory ventilated.
- Do not reach over chemicals or equipment to avoid spillages and breaking equipment.
- Make sure that you are well organised and that all equipment is set up correctly and all chemicals labelled.
- Do not sit down and carry out your titration as this could cause faults in your experiment, always stand up so that you are aware of what you are doing and you can see everything that is going on.
In this experiment I will make sure that I wear a lab-coat and goggles at all times as I am working with harmful chemicals and glassware. I will make sure that I am very careful in handling the equipment and chemicals and avoid spillages, and coming in contact with the chemicals being used.
The plan that I am going to use for this titration, I think is a reliable and accurate method and will give me dependable results. The equipment being used it cleaned out and set-up properly and the chemicals and substances being used are correctly and precisely weighed and measured out. Everything should be done proficiently and skilfully so that reliable values from the titrations are obtained. Equipment such as the pipette filler should be used very carefully so that no errors are made. When as many titration values have been collected, I will calculate the average titre, producing an accurate result.
Something that I cannot stop from happening is human error, which an experiment is always affected by.
If someone else were to follow my planning and method, they would easily be able to understand and follow the instructions, as I have clearly set out the method step by step.
Things to do during my titration so that I obtain accurate and reliable results:
- Make sure that the burette is washed out with distilled water so that no contamination occurs and all impurities gone. If possible rinse out the burette with the solution that it will be filled up with e.g. sulphuric acid, to ensure accurate results.
- When using the weighing scales make sure that you weigh only the sodium carbonate powder and nothing else. Make sure the surface is clean. Before weighing the powder, weigh the watch glass and subtract the weight of it from the powder using the digital scale.
- Make sure that all glassware that is being used is washed fully with distilled water so that no impurities are left behind. This would reduce the chance of contamination.
- The indicator being used will be methyl orange as a strong acid is being neutralized by a weak alkali, so therefore it is more suited. Methyl orange changes from red at pH 3.1 to yellow at pH 4.4. The colour change is very easy to see.
- Make sure that you have a white tile, which is cleaned underneath the conical flask when the titration is taking place, so it is easier for you to see when the solution has changed colour.
- When transferring the sodium carbonate solution into the graduated flask, make sure that absolutely all of the sodium carbonate has been transferred. Do this rinsing out the beaker with distilled water and the glass rod, which was used to stir the solution and add this all the sodium carbonate solution to make the solution up to 250cm³
- Make sure that all the readings taken from the burette are read accurately, so that the bottom of the meniscus is touching the line. This should also be done when filling up the burette with sulphuric acid and using the pipette filler to collect 25cm³ sodium carbonate solution. Always make sure that the reading and when measuring out a solution, is taken from the bottom of the meniscus.
- When measuring out a solution, use a pipette to ensure that the bottom of the meniscus is touching the line so that an accurate volume is obtained. Your eyes should be at eye-level to the mark at which you are aiming for.
- Volumetric flasks ensured accurate results as it had a long neck at the top so that the volume is precise.
- Make sure that the conical flask containing 25cm³ of sodium carbonate solution is washed out after each titration so that no sulphuric acid is left inside. Conical flasks were used as they stopped the solution from spilling out during the swirling in the titration therefore obtained the correct volume throughout the titration.
- The end point of a titration is when the two solutions have the same number of moles at that point. I am aiming to do at least seven titration’s including a rough titration.
Implementing
I have now finished my titration, and have obtained a set of results, which is shown in the table below. I have also shown the different measurements that were taken for all the chemicals that were used for the titration.
-
Amount of Na2CO3 (s) used = 2.65 g
-
Amount of Na2CO3 (aq) used for each titration = 25cm3
-
Concentration of the Na2CO3 (aq) used for each titration =
0.1 mol dm-3
- Temperature of surrounding = 20degrees.
Below is a table showing the final results that I obtained from each titration. I achieved a good set of results as they all only had a difference of 0.1cm between them, which is very accurate. I also involved my rough titration in the table, which is not counted in the final calculations, as it was the only anomalous result that I had.
The rough titration gave me a warning to when the neutralization occurs between the sulphuric acid and sodium carbonate solution, so that I would not add too much acid in my next titration.
Analysis
Na2CO3 (aq) + H2SO4 (aq) Na2SO4 (aq) + H2O (l) + CO2 (g)
By looking at the equation above, we can predict exactly what is going to happen in the reaction. One mole of Na2CO3 will react with one mole of H2SO4 . This will form Na2SO4 which is a neutral salt, water and carbon dioxide.
The two formulas that are needed to find out the concentration of a solution are –
Moles = Mass/Relative Formula Mass
+
Concentration (mol dm-3 ) = Mass/Relative Formula Mass
The concentration will be measured in mol dm-3, therefore in order to use the formulas above, we will have to change the units of the results that we obtained which were in cm3 . The volume has to be measured in dm-3 not cm3 as the concentration is being measured in dm3.
Na2CO3 (aq) + H2SO4 (aq) Na2SO4 (aq) + H2O (l) + CO2 (g)
For the above reaction to take place properly, the molar mass for both Na2CO3 and H2SO4 should be equal. By looking at the equation we can see that this is true. We need to know this, as it will help us find out the concentration of H2SO4, which is unknown.
When working out the concentration of the sulphuric acid, we instantly know that H2SO4 has the same number of moles as Na2CO3 as we have already calculated the molar mass ratio, which is 1 : 1.
(a) Calculate the concentration of the sodium carbonate solution, which you made up.
Moles of Na2CO3 = Mass
Relative Formula Mass
= 2.65
(2x23)+12+(3x16)
= 2.65
106
= 0.025
250cm³ water = 0.25 dm³. Therefore concentration in moldm³ =
Concentration of
Na2CO3 = Moles
Volume (dm3 )
= 0.025
0.25
= 0.1 mol dm-3
(b) Calculate the concentration of sulphuric acid
I already know that the ratio is 1:1, as it takes 1 mole of sodium carbonate to react with 1 mole of sulphuric acid. This is when neutralization occurs. Therefore I can easily work out the concentration of sulphuric acid using the same equation that we used for the sodium carbonate.
But there is a slight change, as we did not use all of the sodium carbonate solution, which was 250cm3, which equals 1 mole.
As 250cm3 of sodium carbonate was made this equals the 1 mole that was calculated which was needed to neutralise the acid, but only 25cm3 of sodium carbonate is used for each titration not 250cm3. This means that only a tenth of the sodium carbonate is used which is 25cm3 of 250cm3. Therefore in order to work out the number of moles of the sulphuric acid that is needed to neutralise the sodium carbonate, we need to divide the number of moles for the volume of 250cm3 of sodium carbonate solution by 10 to get the number of moles for 25cm3.
This gives us the number of moles for sulphuric acid, so that we are able to work out the concentration of sulphuric acid that is used.
Moles of Na2CO3 = 2.65
106
= 0.025 moles
= 0.025
10
Moles of H2SO4 _ = 0.0025
As you can see from the calculation above, we have worked out that 0.0025 moles of sulphuric acid is used to neutralise 0.025 moles of sodium carbonate solution. We can now work out the concentration of sulphuric acid by using the formula below as we have already calculated the number of moles of sulphuric acid.
Concentration of H2SO4 = Moles
(mol dm-3) Volume (dm3)
In order to use the equation above, I will have to change 26.68cm3 into dm3 . The reading 26.68cm3 is my average titre reading that I obtained when doing my titration experiment.
The formula below helps change the reading from cm3 to dm3:
1000 cm3 = 1 dm3
To convert the value to dm3 for the formula to work, the value for the volume obtained in cm3 must then be divided by 1000, as shown below:
x cm3 = x dm3
1000
Concentration of H2SO4 = Moles
(mol dm-3) Volume (dm3)
= 0.0025
(26.68/1000)
= 0.0025 x 1000
26.68
= 0.09 mol dm-3
I have now calculated the concentration of sulphuric acid that is needed to neutralize 25cm3 sodium carbonate solution. 0.09 mol dm-3 of 26.68cm3 is the concentration of sulphuric acid, which is needed to neutralize 25cm3 of 0.1 mol dm3 concentration of sodium carbonate solution.
The result that I have obtained to show the concentration of sulphuric acid that is needed to neutralize 25cm3 of sodium carbonate solution is shown by all the calculations that I have worked out previously. I think that my result is very accurate and reliable as all my results were very close as they only had a difference of 0.2cm3 between them.
My results that were obtained from the titration show that the concentration of sulphuric acid is 0.09 mol dm-3 . This is not the exact value but, it still agrees with the original statement that the acid is thought to have a concentration between 0.05 and 0.15mol dm-3 .
This shows that my results are reliable even though they are not precise.
Even though my results are accurate they are not perfect. There is always some sort of error that affects an experiment. This is called human error. Apart from that, I could have made a few mistakes during the titration, which I might not have been aware of making, which could have affected my final result.
This will all be explained in my evaluation.
Evaluation
By looking at my results and the suitability of the procedure, I can confidently say that my results are accurate and reliable and all the practical work was proficiently and skilfully done.
The values that I obtained are very reliable and useful as they are all very similar. This means that the average titre is highly accurate.
Looking at the graph that is drawn, we can see that the results are reliable; there is only one anomalous result.
Anomalous results
From the graph we can see that there is one anomalous result that does not fit together with the rest of the values. The best line of fit shows us that all the results are in range of the line except the reading - 28.7. This value is way out of range from the other values. This was my first result that I recorded in my preliminary experiment. All the other results obtained in my actual experiment were all accurate.
Percentage error -
Percentage error = Error x 100
Of Na2CO3
= Reading
= 0.005 x 100
2.65
= 0.19%
0.19% - This is the percentage error reading of sodium carbonate powder that was measured on the digital scale.
Percentage error = Error x 100
Of H2SO4
= Reading
= 0.005 x 100
26.67
= 0.019%
0.019% - This is the percentage error reading of average titre needed to neutralise 25 cm3 of Sodium carbonate solution.
The percentage error for the pipette is:
0.005 cm3 x 100 = 0.02%
25
The percentage error for the volumetric flask was:
0.005 cm3 x 100 = 0.002%
250
Total % error _ = 0.19 + 0.019 + 0.02 + 0.002
= 0.231%
Looking at the percentage errors we can see that a lot of mistakes were made during the experiment, which caused these inaccuracies. As the percentage errors are very low, it will not make much of a difference to the final results overall. When the errors are added up together there is a very large overall percentage error that could have made a difference to the results.
These percentage errors could have occurred in many ways during the experiment. Here are some examples of where I could have made these errors:
- The glassware that we were using for the titrations might have not been cleaned properly leaving other chemical impurities to react with the chemicals that we were using. This could have made a difference to the final result.
- When taking the reading of the burette, I could have misread the value or not taken the reading from the bottom of the meniscus therefore recording an inaccurate result.
- Different bottles of methyl-orange were used. This could have affected the final result, as some methyl-orange liquids were darker than others. Also the size of the drops varied, therefore this could have changed the final result also.
- The solution of sodium carbonate made up in the volumetric flask might not have been shaken well; therefore the substances not mixed properly resulting in different concentrations of sodium carbonate for each titration.
-
When transferring 25cm3 of sodium carbonate solution into the conical flask using the pipette filler, all of the solution may not have been transferred properly, therefore leaving a few drops in the pipette filler. This results in different amounts of sodium carbonate solution being less than it should be for each titration. This could affect the final results.
- As the burette is controlled by hand the number of drops added to the sodium carbonate is varied. More drops of the acid could have been added to the solution than needed, resulting in different sulphuric acid concentrations.
If I could repeat the whole experiment I would make these changes:
- Make sure that all the equipment being used is thoroughly cleaned with distilled water leaving it dirt free, so that the chemicals being used will not be contaminated during the experiment.
-
When transferring the sodium carbonate solid from the watch glass to the beaker, make sure that all of the solid is transferred by washing the contents on the watch glass into the beaker using distilled water so that exactly all of the 2.65cm3 of sodium carbonate is transferred into the beaker.
- Make sure that the burette is correctly placed so that your eyes are level to the 0 mark, where the sulphuric acid is filled up to. Make sure that the bottom of the meniscus touches the 0 line for accurate results.
- Using the pipette to fill up the burette insured that the amount of acid was accurate.
- When you have filled the burette with acid remove the funnel so that the extra acid left in the funnel will not drip into the burette and therefore may affect the result for the titration.
-
Before starting the titration makes sure that the white tile that your flask containing your 25cm3 sodium carbonate solution, will lye on during the titration is clean so that you can clearly see when the sodium carbonate solution has changed its colour.
- The methyl orange indicator was used in the experiment because it matches the solution and the colour is easy to see.
- When you have started your titration make sure that you have full control of the acid that is running through the tap into the flask. Make sure that you have had a practice with using the burette tap so that you can control it. As you come closer to the point of neutralization make sure that the acid is being added to the sodium carbonate solution at a very slow pace so that you can immediately stop the tap once the solution has changes colour. Make sure that the flask is being swirled in circles while the acid is being added so that the sulphuric acid is completely mixed with the sodium carbonate.
- At the end of each titration, record the value that is shown on the burette. When starting a new titration make sure that the volumetric flask that contained the sodium carbonate solution is fully rinsed out so that it does not mix with the new batch of sodium carbonate solution and therefore affect the result.
- Using a volumetric flask is more suitable for this titration than a normal beaker because the shape of the flask makes it easier to hold and swirl the flask so that no splashes occur.
- To make this titration more accurate, a pH meter could have been used, instead of the pH indicator. A pH meter would tell us exactly when the point of neutralization occurs. This could prevent human error as we could have added too much acid solution, which might have not been needed. This would make the final result much more accurate.
- Another equipment that could have been used is a light detector and a beam of light shone through the volumetric flask, to immediately detect colour change of the solution. This would also prevent human error.
- To prevent human error is to practice using the equipment that will be used for the titration. This would greatly improve the titration value. Practice in reading the burette and making sure that you read the bottom of the meniscus is vital. Also controlling the tap of the burette is also needed so that not too much acid is added to the sodium carbonate solution.
Other ways that I could have improved my experiment would be to:
- The use of high-tech equipment in this titration could have made a big difference to the experiment and would have given us an even more accurate result. It would have eliminated most of the human error that occurred in this experiment to give us a much more reliable result.
-
Using high-tech equipment to make your sodium carbonate solution would have been a great advantage, as it would make sure that all of the sodium carbonate has been dissolved into the distilled water and so nothing is left behind. Also when transferring the solution into the graduated flask and using a pipette filler to measure out 25cm3 of sodium carbonate, the high-tech equipment would make sure that the volume is correct and that the bottom of the meniscus touches the mark. It would also get rid of any air bubbles.
- Another thing that could have affected this experiment is the impurities and dirt that could have been left behind in the equipment that were being used. This could have been because they were not rinsed out or cleaned properly. The use of high-tech equipment could have detected these impurities and gotten rid of them straight away so that conditions were perfect.
- A large part of the titration, which could have been affected by human error, was when handling the sulphuric acid flow through the tap. As human hands controlled the acid flow, the flow was not controlled. More acid could have been added then needed, therefore making the result inaccurate. This could have been dealt with if high-tech equipment could have been used. This would have controlled the acid flow from the tap making the result accurate. Equipment also could have been used to detect the colour change in the conical flask at the precise time of neutralisation. This would have been more efficient as our eyes might not have been able to adjust to the colour change so quickly.
Overall, I think that the results that I have obtained are very accurate and reliable as they tell me what I wanted to find out for this titration. If I wanted an even more accurate result I would use the techniques referred to in my evaluation. I would without a doubt use high-tech equipment as there was a lot of human error in my titration experiment. Also instead of a pH indicator I would have used a pH meter as it would have given me the exact value at which neutralisation occurs.
