chemistry - 3e - volumetric analysis

Question 1

What is a standard solution?

Answer 1

A solution of accurately known concentration.

Question 2

How can standard solution be prepared?

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 another way of preparing standard solutions?

Answer 3

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

Question 4

What must a primary standard be?

Answer 4

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

Question 5

What are some examples of primary standards?

Answer 5

• sodium carbonate
• hydrated oxalic acid
• potassium hydrogen phthalate
• silver nitrate
• potassium iodate
• potassium dichromate

Question 6

Why is sodium hydroxide not a primary standard?

Answer 6

As it has a relatively low
GFM, is unstable as a solid (absorbs moisture) and unstable as a solution.

Question 7

What must happen to sodium hydroxide before being used in volumetric analysis?

Answer 7

It must be standardised.

Question 8

What is EDTA?

Answer 8

An important complexometric reagent and can be used to determine the concentration of metal ions in solution.

Question 9

What are back titrations used for?

Answer 9

To find the number of moles of a substance by reacting it with an excess volume of a reactant of known concentration.

Question 10

In a back titration, what happens to the resulting mixture?

Answer 10

It is then titrated to work out
the number of moles of the reactant in excess.

Question 11

When is a back titration useful?

Answer 11

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