Definition:-Titration is a technique used to determine the concentration of a solution by adding a solution of known concentration with an indicator.
What is a standard solution?
A standard solution is a solution whose concentration are accurately known to us.
Primary standard solution?
A standard solution prepared from a solid.
Properties of a primary standard solution:
I. Highly pure
II. Reacts completely
III. Must have stable masses
V. No moisture(NaOH is a poor primary standard solution as it quickly absorbs moisture from the air and its mass increases)
Secondary standard solution?
Standard solution whose concentration was determined using titration/others quantitative analysis.
Steps To Titrating:-
I. Rinse a clean burette with a small amount, say 5-10 ml, of the solution of known concentration. Discard.
II. Overfill the burette with this known solution and run the excess out. The solution level should now be on the zero mark (The bottom of the meniscus should be touching the 0 ml mark). This solution is known as the titrant.
III. Use a pipette to measure a given volume of the solution of unknown concentration into the flask and place it under a burette.
IV. Add three drops of suitable indicator to the flask.
V. A white surface under the flask will make the end point easier to determine. Slowly run the titrant into the flask swirling continuously. Near the equivalence point add the titrant drop wise until the indicator just changes colour and there is no further colour change.
VI. Accurately read the volume of the titrant delivered on the burette.
VII. Repeat the titration at least three times to obtain end points as close as possible. If a value deviates significantly from the others, ignore it and replace it with another titration.
VIII. Average your three (Close) titrant volumes.
IX. Calculate the concentration of the solution of unknown concentration.
X. NOTE: Always wash the burette with the acid and the flash and the pipette with the base which are given to you. Do not wash it with water as it can change the concentration of the solution, which can affect the outcome quite significantly.
Determine The End Point Of An Titration:-
In determining the end point of a titration, an appropriate indicator needs to be used.
I. Strong acid/strong base titrations have an end point around pH=7. An appropriate indicator to use is, for example, bromothymol blue. This indicator changes colour from yellow ( pH=6.7) to blue (pH=7.6)
II. Weak acids/ strong base titrations have an end point around pH=9. An appropriate indicator to use is, for example, phenolphthalein. This indicator changes colour from colourless (pH=8.2) to pink (pH=10.0).
III. Strong acid/weak base titrations have an end point around pH=4. An appropriate indicator to use, is for example, methyl orange. This indicator changes colour from red (pH=3.2) to yellow (pH=4.4). End Points and Equivalence Point
End Point: - The point where the indicator changes colour
Equivalence Point: - The equivalence point is the point where the number of moles of base is