(P) Titrations

• Titrations are used to find out concentrations
• Titrations allow you to find out exactly how much acid is needed to neutralise a quantity of alkali - or vice versa. You can use this data to work out the concentration of the acid or alkali
• 1)Say you want to find out the concentration of some alkali. Using a pipette and pipette filler, add a set volume of the alkali to a conical flask. Add 2 or 3 drops of indicator too

  
• 2)Use a funnel to fill a burette with some acid of known concentration. Make sure you do this below eye level - you don't want to be looking up if some acid spills over (also wear safety goggles). Record the initial volume of the acid in the burette

  
• 3) Using the burette, add the acid to the alkali a bit at a time - giving the conical flask a regular swirl. Go especially slow when you think the end-point (colour change) is about to be reached

  
• 4)The indicator changes colour when all the alkali has been neutralised, e.g. phenolphthalein is pink in alkaline conditions, but colourles in acidic conditions

  
• 5) Record the final volume of acid in the burette, and use it, along with the initial reading, to calculate the volume of acid used to neutralise the alkali

  
• To increase the accuracy of the titration and spot any anomalous results, you need several consistent readings
• The first titration you do should be a rough titration to get an approximate idea of where the solution changes colour (end-point). You then repeat the whole thing a few times, making sure youget almost the same answer each time (within 0.10 cm^3)
• At the end, calculate a mean of your results, ignoring any anomalous results
• Pipette

  • Pipettes measure only one volume of solution. Fill the pipette to about 3 cm above the line, then carefully drop the level down to the line

  
• Burette

  • Burettes measure different volumes and let you add the solution drop by drop