Amount of Substance: Titrations

Question 1

What are Titrations?

Answer 1

• Titrations are a form of volumetric analysis

• Include a neutralisation reaction
• Known volume and concentration of a solution is reacted with a measured volume of a solution - enables you to calculate concentration of unknown substance

Question 2

Making a Standard Solution

Answer 2

• Solution with a known concentration, used in titrations
- Making a standard solution involves dissolving a known amount of solid in a known amount of water to create a known concentration

• Carefully weigh out the required mass of your solute
• Dissolve the solute in your chosen solvent (water) in a beaker by stirring with a glass rod
• Transfer your solution to a volumetric flask using a funnel
• Rinse the beaker and funnel with the initial solvent, adding the washings into the volumetric flask
• Add some of your solvent to the volumetric flask. Make up to the graduation line
• Add solvent, drop by drop, until the bottom of the meniscus is sitting on the line. Do not allow the solution to fill above the line
• Mix solution thoroughly. Invert flask multiple times

Question 3

Making a Standard Solution: Initial Calculations

Answer 3

• Calculate number of moles needed using
- moles = concentration x volume

• Calculate Mr

• Calculate mass
- Mass = Mr x moles

Question 4

Method for Titration

Answer 4

• Rinse burette with standard solution
• Pour analyte into a beaker
• Use pipette to transfer a recorded volume of analyte to a conical flask
• Add chosen indicator to analyte, swirl and record colour
• Titrate the analyte by adding titrant using a burette, while continuously swirling the conical flask
• Use a wash bottle of distilled water to rinse sides of conical flask if solution splashes on the sides
• Add titrant dropwise near the end-point until the indicator undergoes a definite colour change
• Record colour change and final burette reading
• Calculate volume of titrant used
• Repeat titration until you obtain at least two concordant results (carry out at least three titrations)
• Calculate and record mean titre volume

Question 5

Calculating Uncertainties

Answer 5

% uncertainty = (uncertainty / measurement made on apparatus) x 100