I am going to conduct an experiment to find the amount of acid in a solution using the titration technique. I have been told that the acid is in between 0.05 and 0.
15 mol dm-3, so I will find the concentration by neutralising a 0.10 mol dm-3 concentrated solution of sodium carbonate.Equipment:- Burette- Pipette (25 cm3)- Clamp Stand- Conical Flask (250 cm3)- Measuring Cylinder- Sulphuric Acid Solution (between 0.05 and 0.15 mol dm-3)- Solid Anhydrous Sodium Carbonate- Phenolphthalein Indicator Solution- Distilled Water- Access to a Balance- Beaker (250 cm3)- Funnel- Small Container- White TileMethod:First you must make up a Sodium Carbonate Solution. To do this you weigh out 2.
65g of the anhydrous sodium carbonate. You transfer the sodium carbonate to a 250 cm3 beaker, washing out the container you weighed it in with distilled water, and tipping the water into the 250 cm3 beaker also. This collects any residue which may be left in the weighing container. You then top up the solution in the 250 cm3 beaker with distilled water until it reaches 250 cm3. Shaking the solution will now allow the Sodium Carbonate to dissolve completely into the water.Now that the Sodium Carbonate Solution is made, we can set up the Burette. Suspend the burette above a small container on a white tile, using the clamp stand. Put the funnel on the top of the burette, and pour the Sulphuric acid through the funnel into the Burette.
Fill the burette a little bit past the line. Now drain the acid through the valve into the container until the acid reaches the line. This allows the acid to fill the valve at the bottom, allowing for better results. The acid in the container must now be washed out and not used as it may be contaminated.Next the Conical Flask will be set up.
Make sure all of the Sodium Carbonate is completely dissolved in the water. Shake the solution once more and use the Pipette to extract 25 cm3 of the solution. Transfer this to the Conical Flask.Now we must add 3 drops of the chosen indicator. Since the Acid is a strong acid and the Alkali is weak, I have chosen Phenolphthalein, an indicator known to work well in these conditions. The indicator will turn colourless when the solution is neutralised.
Now place this conical flask under the burette. Place the conical flask on top of the white tile underneath the Burette. The white tile makes it easier to notice the change in colour.
Now the experiment is ready to be started. To titrate, you must shake the conical flask (to mix the solution evenly), whilst adding the acid slowly to the solution. The first time this is done will be a rough titre, to see roughly where you need to slow the addition of the acid. You should simply add the acid to the solution until it turns colourless.
For the next titres however, you must be more careful, as you must try and find the last drop which turns the solution colourless. You should aim for 5 titres, however, it is important to try and get 3 titres within 0.1 of each other. This shows that you have successful results. If you do not have 3 titres within 0.1 of each other then you must continue to do further titres until you have 3 successful titres. It is important that each time you do a titre, you must wash out the equipment (apart from the Burette and the 250 cm3 Beaker) with distilled water thoroughly, to reduce contamination, providing better results.
Safety:During the entire experiment I will wear my safety goggles and lab coat. The goggles will protect my eyes from contact with the acid, which is an irritant. The lab coat will protect my clothes from spillages. I will wear gloves when handling the sodium carbonate, as it is an irritant. The sulphuric acid is corrosive and must be handled with care. I shall take care not to inhale the fumes from the Phenolphthalein.ImplementingI carried out the experiment as stated in the planning section. Below are the results and evaluation of these results.
Results:Evaluation of Accuracy:There must be some inaccuracy in my results, otherwise they would all be the same. This type of inaccuracy will always be there, but we can overcome most of this by taking averages. These inaccuracies, however small, must still be addressed.
One of the main point of inaccuracy cannot be measured. This of course is the human error factor which will be there always. We can however put a value on the percentage error of the equipment. We find this by this formula:Percentage Error = Error x 100Reading-The Pipette has a percentage error of 0.
06 cm3, the reading was 25 cm3. Using the formula I calculated the percentage error of the Pipette as 0.24%.-The Burette’s error is 0.
05 and its reading was 50 cm3. This means it has a percentage error of 0.1%-The volumetric flask also has a percentage error. This is 0.2 cm3 and it’s reading was 250 cm3. This calculates to a percentage error of 0.08%.
This means that the Pipette was the item of equipment which contributed most to the error in the experiment, whereas the Burette was the next highest contributor, and the flask barely affected the accuracy at all.Evaluating Evidence:The average titre (the most consistent result) was 14.20 cm3. This means that it takes 14.20 cm3 of The Sulphuric acid solution to exactly neutralise 25.
00 cm3 of 0.10 molar Sodium Carbonate solution. 1 mol of Sodium Carbonate will neutralise 1 mol of Sulphuric acid. One dm3 (1000 cm3)of sodium carbonate contains 1 mol.
Therefore, 25.00 cm3 Sodium Carbonate solution contains: (25 x 0.1) = 0.0025 mols.
1000If 0.0025 molar Sodium Carbonate solution neutralises 0.0025 molar Sulphuric Acid then 14.20 cm3 of Sulphuric acid contains 0.
0025 mols. 1 cm3 of Sulphuric Acid contains (0.0025) = 0.0000176 x 1000 = 0.18 mols of Sulphuric Acid.14.20Therefore the solution of Sulphuric Acid was a 0.18 molar solution