Given this information I can work out that methyl orange will be the most suitable indicator to use because we are using sulphuric acid, being a strong acid and sodium carbonate, being a weak alkali.
Before the experiment can begin we need to work out what the end products of the reaction will be because an acid plus a carbonate gives us acid-salt, water and carbon dioxide and we need to find out what the salt is.
Carbonate + acid → Salt + H2O + CO2
Na2CO3(aq) + H2SO4(aq) → Na2SO4(aq) + H2O(l) + CO2(g)
Having worked this out I can see that it is a 1:1 ratio meaning the moles of each substance in the end solution will be equal. As you see both solutions need to be aqueous so I will make up the sodium carbonate solution to 0.1 mol dm-3, this is between 0.05 and 0.15, which is thought to be the concentration on the acid. Then I will find out the relative molecular mass of sodium carbonate by adding up the mass of each element in the compound of Na2CO3.
2 x Na (23) =46
1 x C (12) = 12
3 x O (16) = 48
= 106
Now I want to make a 250cm3 solution at 0.1 mol.
Having worked out the relative molecular mass of sodium carbonate I know that I need 106g of Na2CO3 to make one mole of solution in 1dm3. But as I only want 0.1 mol dm-3 I would only need 10.6g. Even now this is too much Na2CO3 as we are using 0.25dm3(250cm3) not 1dm3(1000cm3) so finally we need to divide 10.6 by 4 to give us 2.65g of Na2CO3 which is correct for 250cm3.
Apparatus:
-Stand
-Clamp
-Pipette
-Pipette Filler
-Burette
-Volumetric Flask
-Digital Balance
-Wash Bottle
-Glass Rod
-Beaker
-Conical Flask
-White Tile
Diagram of apparatus and lay-out of results table
Figure 1: diagram of apparatus and table for results
Method
To begin with I will weigh out as accurately as I can 2.65g of anhydrous sodium carbonate into a weighing bottle and will then transfer this into a large beaker to make the solution. I will rinse the remains in weighing the bottle into the beaker so I ensure all the sodium carbonate gets transferred. I will then add distilled water to the beaker and stir the solution with the glass rod until all the anhydrous sodium carbonate has dissolved. I will rinse the sides of the beaker with the wash bottle to ensure accuracy. Using a funnel I will transfer the solution into a volumetric flask and getting it as close as possible to the white line, then using the pipette I will ensure that the bottom of the meniscus is touching the white line. Putting the stopper in the flask I will then invert it several times to ensure the solution is mixed properly.
Next the stand and the clamp need to be set up, but before the burette can be attached it needs to be rinsed out with the sulphuric acid and a little run through to ensure the jet is full. Then ensuring that my eyes are at the same level as the burette measures I will add the acid to burette and fill it. Using the white tile and placing it behind the burette for better visibility I will obtain a more accurate reading of 0. Using the pipette and pipette filler, 25cm3 of the solution is added to a conical flask along with 3 drops of methyl orange ready for titration. Place the white tile underneath the conical flask so it makes it easier to determine the colour change.
Firstly I will do a rough titration so I will know approximately how much needs to be used for the mixture to change colour. This will help me with my accurate readings as I will know when to add the acid cautiously to avoid adding too much. Now the recorded runs can be done and as you reach closer to the mark you need to begin adding acid drop by drop, whilst swirling the flask the whole time. The titration must be stopped as soon as the methyl orange turns a pink/peachy colour. The titration must be repeated until you achieve concordant results within 0.1cm3 of each other.
Safety Precautions
Anhydrous Sodium Carbonate;
Is an irritant to the eyes and respiratory system and the dust must not be breathed in. In case of contact with eyes, they must be rinsed immediately with plenty of water and medical advice must be sought. Exposure to the dust must be minimized.1
Sulphuric Acid;
Extremely corrosive and causes serious burns. It is highly toxic and harmful by inhalation, ingestion and through skin contact. Ingestion may be fatal. Skin contact can lead to extensive and severe burns. Chronic exposure may result in lung damage and possibly cancer. Safety glasses or a face mask must be worn. Acid resistant gloves should be worn and there must be suitable ventilation because the vapour mustn’t be inhaled.2
You must be stood up and the safety goggles must be kept on at all times during the experiment. Long hair must be tied back. Spillages must be cleaned up immediately and broken glass must be safely disposed of in the ‘broken glass’ waste bin.
References
Fig 1: http://www.avogadro.co.uk/miscellany/titration/apparatus.gif
1 http://msds.chem.ox.ac.uk/SO/sodium_carbonate_anhydrous.html
2 http://msds.chem.ox.ac.uk/SU/sulfuric_acid_concentrated.html
Heinemann Salters Advanced Chemistry: Chemical Ideas – Pages 12-13
