Ch 11 Volumetric Analysis
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Volumetric Analysis A quantitative technique used to analyse solutions using volumes of solutions.
…involves the addition of a standard solution (from a burette) to a known volume (in a conical flask) …process is known as “titration”
Titration A titration is a method of analysis that will allow you to determine the precise endpoint of a reaction and therefore the precise quantity of reactant in the titration (conical) flask. A burette is used to deliver the second reactant to the flask and an indicator or pH Meter is used to detect the endpoint of the reaction.
Burette (50 cm3 capacity)
Rinse burette with distilled water, then twice with 10 ml portions of the solution you intend to put into it. Remember to flush the jet of the burette with the solution as well Fill up the burette with the help of a filter funnel, removing it after use. Ensure no air bubbles are trapped in the jet. Nearer the end-point, the liquid should be delivered drop-bydrop.
Pipette (10.0, 20.0, 25.0 cm3 capacity)
Rinse pipette with distilled water, then twice with a little of the solution you intend to put into it. Fill up the pipette using the pipette filler. If air bubbles are present, restart. Hold vertically. Once pipette is filled up, quickly, remove the pipette filler and put your index finger on the end of the pipette. Gently release the seal made by your finger until the level of the solution meniscus exactly lines up with the mark on the pipette. Practice this with water until you are able to use the pipette and filler consistently and accurately. Let the liquid drain from the pipette into the conical flask. Dip the tip of the pipette into the solution (in the conical flask) to release the last bit of liquid – do not blow out.
Conical flask
Should be washed clean and must be rinsed with distilled water (twice). Need not be dry, distilled water does not affect the number of moles of substance in the flask. Place a white tile or a sheet of white paper under the conical flask so that colour changes can easily be seen. Swirl the contents in the conical flask while dispensing the liquid from the burette – this takes a bit Right-handed students: of skill.
Right hand – conical flask Left hand – burette tap
Indicators Indicator Methyl orange Screenedmethyl orange
Colour in acidic solution Red/Pink Magenta
Phenolphthalein Colourless
Colour in Colour in “neutral” alkaline solution solution PeachYellow Orange Grey
Green
Pale pink
Red
Recording Titration values Titration number Final reading/cm3 Initial reading/cm3 Volume of P used/cm3 Best titration results(√)
Very rough titration – do it fast!
1
2
3
27.5
26.2
36.2
0.0
0.0
10.1
27.5
26.2
26.1
√
√
Average volume of P used for titration is 26.2 + 26.1 ÷ 2 = 26.15 cm3
…involves the addition of a standard solution (from a burette) to a known volume (in a conical flask) …process is known as “titration”
Titration A titration is a method of analysis that will allow you to determine the precise endpoint of a reaction and therefore the precise quantity of reactant in the titration (conical) flask. A burette is used to deliver the second reactant to the flask and an indicator or pH Meter is used to detect the endpoint of the reaction.
Burette (50 cm3 capacity)
Rinse burette with distilled water, then twice with 10 ml portions of the solution you intend to put into it. Remember to flush the jet of the burette with the solution as well Fill up the burette with the help of a filter funnel, removing it after use. Ensure no air bubbles are trapped in the jet. Nearer the end-point, the liquid should be delivered drop-bydrop.
Pipette (10.0, 20.0, 25.0 cm3 capacity)
Rinse pipette with distilled water, then twice with a little of the solution you intend to put into it. Fill up the pipette using the pipette filler. If air bubbles are present, restart. Hold vertically. Once pipette is filled up, quickly, remove the pipette filler and put your index finger on the end of the pipette. Gently release the seal made by your finger until the level of the solution meniscus exactly lines up with the mark on the pipette. Practice this with water until you are able to use the pipette and filler consistently and accurately. Let the liquid drain from the pipette into the conical flask. Dip the tip of the pipette into the solution (in the conical flask) to release the last bit of liquid – do not blow out.
Conical flask
Should be washed clean and must be rinsed with distilled water (twice). Need not be dry, distilled water does not affect the number of moles of substance in the flask. Place a white tile or a sheet of white paper under the conical flask so that colour changes can easily be seen. Swirl the contents in the conical flask while dispensing the liquid from the burette – this takes a bit Right-handed students: of skill.
Right hand – conical flask Left hand – burette tap
Indicators Indicator Methyl orange Screenedmethyl orange
Colour in acidic solution Red/Pink Magenta
Phenolphthalein Colourless
Colour in Colour in “neutral” alkaline solution solution PeachYellow Orange Grey
Green
Pale pink
Red
Recording Titration values Titration number Final reading/cm3 Initial reading/cm3 Volume of P used/cm3 Best titration results(√)
Very rough titration – do it fast!
1
2
3
27.5
26.2
36.2
0.0
0.0
10.1
27.5
26.2
26.1
√
√
Average volume of P used for titration is 26.2 + 26.1 ÷ 2 = 26.15 cm3
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