Here is the procedure which is required for preparing my standard solution.
Procedure:
1: Using a spatula transfer 2.54g of sodium carbonate to the weighing boat. Weigh the sodium carbonate and weighing boat in the balance, and make sure that you have exactly 2.54g of sodium carbonate, weighing to the nearest 0.01g.
2: Put about 50cm of distilled water into a 250cm beaker. Carefully transfer the bulk of the sodium carbonate from the weighing boat into the beaker.
3: Reweigh the bottle with any remaining sodium carbonate to the nearest 0.01g.
4: Stir to dissolve the solid using the stirring rod, and add more distilled water if necessary.
5: Transfer the solution to the volumetric flask through the filter funnel. Rinse the beaker well, making sure all of the liquid goes into the volumetric flask.
6: Add distilled water until the level is within about 1cm of the mark on the neck of the volumetric flask. Insert the stopper and shake to mix the contents.
7: Using a dropping pipette, add enough distilled water to bring the bottom of the meniscus to the mark. Insert the stopper and shake thoroughly ten times to ensure complete mixing. Simply inverting the flask once or twice does not mix the contents properly and is a very common fault.
8: Label the flask with the contents, your name and the date. Set aside the flask for the titration.
Now here is the details of the actual titration, showing the equipment to be used and the quantities of materials. There is also a labelled diagram which shows the set-up of the apparatus, and should help when setting up the equipment for the practical.
Volumetric analysis, determining the concentration of acid:
Requirements:
- safety glasses
- tripod stand
- 2 clamps
- white tile
- conical flask
- burette
- distilled water
- dropping pipette
- sulphuric acid, 25cm
- filter funnel
- sodium carbonate, 2.54g
- methyl orange, few drops
Here is the procedure by which the titration will be carried out.
Procedure:
1: Set-up the stand and the burette, held firmly in position by the clamps, you can refer to the diagram as above.
2: 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.
3: 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.
4: Add a few drops of the methyl orange indicator to the conical flask (methyl orange is being used as the titration is between a strong acid and a weak alkali).
5: Now perform a rough titration by running the sulphuric acid, whilst swirling the flask of alkali, until the indicator turns a pink colour. This is the end point where the acid and the alkali have neutralised each other. Note and record the rough value of the volume of acid in a table.
6: Now perform a second titration, this is as before except that this time run in the acid until about 2cm less than the rough value has been added, then proceed to run in the acid a drop at a time keeping a close eye on the colour of the solution. Record this end point in the table as before. Remember to use the pipette as before with the exact same volume of the standard solution, and the exact same volume of sulphuric acid.
7: Continue to do the titrations until you get two readings within 0.1cm of each other. Remember to record the volume of sulphuric acid required each time. Now work out the average of the accurate readings and record this in the same table.
Once the titrations have been completed and a sufficient average value has been calculated, I can go on to evaluate and analyse the experiment. Here is a risk assessment of the chemicals used in my experiment.
Risk assessment:
Sodium carbonate:
The sodium carbonate is very dilute and so should induce very little harm, although normal laboratory precautions should be applied. Avoid contact with eyes, skin and clothing. Make sure that any spillage's are immediately tended to, for the sake of other people, as floor may become slippery.
Methyl orange:
Again methyl orange is very dilute in the solution and so should cause very little harm, despite being an azo compound. Same laboratory precautions apply to methyl orange as sodium carbonate.
Sulphuric acid:
Concentrated sulphuric acid is a colourless, viscous liquid reacting vigorously with water. As the sulphuric acid I'm using only has a concentration of between 0.05 and 0.15cm therefore it is not very harmful. Prevent contact with skin and eyes and clean up any spillage's. The dilute acid irritates the eyes and may cause burns; it will irritate the skin and may give rise to dermatitis.
Explanation:
My plan for the titration should provide precise and reliable results if all chemicals are weighed and measured to the correct mass or volume. The apparatus should be set-up properly with no judgmental errors such as the reading of the volume on the dropping pipette or burette. This is the table by which I will be recording the volumes of sulphuric acid used in the titration, hence my results, I will calculate the average volume from these results. Using this form of table should allow me to provide a clear and concise way of representing my results and should aid me in my analysing and evaluating section of this investigation.
Accurate (cm)
Rough (cm) 1 2 3 4 5 etc
Final burette reading
Initial burette reading
Volume of acid required
There will be a certain degree of error in my experiment, which is inevitable, this will be revisited in the analysing section and includes mathematical error. My plan is very clear and shows a step by step view of carrying out the titration, including the equipment to be used. If another student were to use this they would find it very easy to follow and would easily be able to carry out the exact same titration using my instructions. The diagram provided gives a good clear indication of the set-up and should help setting up the apparatus for real.
Sources:
-
Chemical Ideas – Salters Advanced Chemistry (2nd Edition).
-
Chemistry – Ann and Patrick Fullick (2nd Edition).
- Activity Guide (What's In a Medicine) – Salters Advanced Chemistry.
- Information sheet on the use if indicators in acid alkali titrations.
-
Hazards in the Chemical Laboratory – Edited by G.D Muir (2nd Edition).
Duncan Beard