Assessed Practical: Titration

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Aoife Gaffney        

Assessed Practical: Titration

Planning assessment

The apparatus to be used:

  • Beaker
  • 250cm 3 volumetric flask
  • Funnel
  • Burette
  • Pipette
  • White tile
  • Conical Flask
  • Balance
  • Spatula
  • Weighing bottle
  • Glass rod

Method 

Making a standard solution:

A weighing bottle was accurately weighed and approximately 5g of anhydrous sodium carbonate was added and the weight of the bottle plus the solid recorded. The anhydrous sodium carbonate was then transferred into a 100cm3 clean beaker. The bottle was carefully rinsed out two or three times with water and the washings were transferred to the beaker each time. About 25cm3 of water was poured into the beaker and stirred with a glass rod until the solid had completely dissolved. This solution was then added to a 250cm3 volumetric flask using a funnel. The beaker and funnel were swilled thoroughly using a small amount of water these washing were then added to the volumetric flask. Water was then added to the volumetric flask until it was about 1cm below the graduation mark. The water was then added slowly from a clean pipette so that at eye level the bottom of the meniscus was just touching the graduation mark. The volumetric flask was then stoppered and then inverted.  

Carrying out a titration:

A conical flask was swilled out with water and a pipette and pipette filler were used to withdraw 25.0cm3 of the sodium carbonate solution from the volumetric flask and transfer it to the conical flask. A burette was first swilled with sulphuric (VI) acid using a clean, dry beaker and a funnel and then filled to below the zero mark. A little of the solution was then run out of the burette into the beaker and the funnel removed. A white tile was then placed underneath the conical flask and a few drops of the indicator methyl orange was added to the sodium carbonate solution. The amount of sulphuric (VI) acid in the burette recorded by seeing at eye level what mark the bottom of the meniscus touched to the nearest 0.05cm3. The sulphuric (VI) acid was then added to the sodium carbonate solution in small volumes until the sodium carbonate solution had turned orange. The amount of sulphuric (VI) acid left in the burette was measured and the amount added to the sodium carbonate was then recorded by subtracting the final reading of the burette from the initial one. This was a rough titration; more titrations were done until there were three volumes which agreed to within 0.1cm3.         

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Justifications

The funnel was removed from the burette before reading it as drops of sulphuric (VI) acid could have fallen into the burette after the reading was taken which would have made the readings inaccurate and larger then it should have been. A white tile was placed underneath the conical flask so that any colour changes could be observed more clearly as the white would contrast with orange. The burette was read at eye level to avoid any parallax errors, as this is where the best view of the meniscus is, and from different angles the water ...

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