Acid-base titrations

Question 1

Uses of titration

Answer 1

• Finding the concentration of a solution
• Identification of unknown chemicals
• Finding the purity of a substance: Tiny amount of impurity in a drug could cause great harm on patient so checking purity is v important

Question 2

Standard solution

Answer 2

• Solution of known concentration.
• Volumetric flask is used to make up a standard solution very accurately.
• Standard solutions are made by dissolving a known amount of solid in a known amount of water to create a known concentration.

Question 3

Preparing standard solutions

Answer 3

1) Solid is weighed accurately.
2) Solid is dissolved in a beaker using less distilled water than will be needed to fill vol. flask to the mark.
3) Solution is transferred to vol. flask. Rinse beaker w/ distilled water and add to vol. flask.
4) Flask is carefully filled w/ distilled water using pipette until meniscus is at the mark. Too much water = too dilute = must be prep. again
5) Vol. flask is slowly inverted many times to mix the solution. If this stage is missed, titration results will not be consistent.

Question 4

Acid-base titration

Answer 4

1) Add measured volume of 1 solution to a conical flask using pipette.
2) Add other solution to burette and record initial burette reading.
3) Add few drops of indicator to solution in conical flask.
4) Run solution in burette into the solution in conical flask, swirling the conical flask to mix the solutions. Eventually indicator changes colour at end point of titration. End point is used to indicate the volume of one solution that exactly reacts with the volume of the second solution.
5) Record the final burette reading. The volume of solution added from the burette is called the titre, which is calculated by subtracting the initial from the final burette reading.
6) A quick, trial titration is carried out first to find the approx. titre.
7) The titration is repeated accurately, adding solution dropwise as end point is approached. Further titrations are carried out until 2 accurate titres are concordant.

Question 5

Indicators

Answer 5

• Methyl orange: yellow to red when acid to alkali

- Phenolphthalein: pink to colourless when acid to alkali