4e- Volumetric analysis

Question 1

What is a standard solution?

Answer 1

A solution of accurately known concentration

Question 2

What are the steps to preparing a standard solution?

Answer 2

• weighing a primary standard accurately
• dissolving in a small volume of solvent (usually deionised or distilled water) in a beaker
• transferring the solution and rinsings into a volumetric flask
• making up to the graduation mark with solvent
• stoppering and inverting

Question 3

What is the other method of preparing a standard solution?

Answer 3

By accurate dilution by pipetting an appropriate volume of a standard solution in a volumetric flask, making up to the graduation mark with solvent, stoppering and inverting

Question 4

What must a primary standard be?

Answer 4

• available in a high state of purity
• stable when solid and in solution
• soluble
• have a reasonably high GFM

Question 5

What are examples of primary standards?

Answer 5

• sodium carbonate, Na2CO3
• hydrated oxalic acid, H2C204-2H20
• potassium hydrogen phthalate, KH(C8H4O4)
• silver nitrate, AgNO3
• potassium iodate, KIO3
• potassium dichromate, K2Cr2O7

Question 6

Why is sodium hydroxide not a primary standard?

Answer 6

It has a relatively low GFM, is unstable as a solid (absorbs water) and unstable as a solution

Question 7

What is EDTA used for?

Answer 7

In complexometric titrations as a reagent to determine the concentration of metal ions in a solution

Question 8

When is a back titration useful?

Answer 8

When trying to work out the quantity of substance in a solid with a low solubility