experiments: volumetric analysis

Question 1

how can a standard solution be prepared?

Answer 1

• 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 2

what’s another way of preparing a standard solution?

Answer 2

by accurate dilution by pipetting an appropriate volume of a standard solution into a volumetric flask

Question 3

give examples of primary standards (6)

Answer 3

sodium carbonate

hydrated oxalic acid

potassium hydrogen phthalate

silver nitrate

potassium iodate

potassium dichromate

Question 4

what is a standard solution?

Answer 4

one of accurately known concentration and can be prepared directly from a primary standard

Question 5

what are primary standards?

Answer 5

Can be used to prepare a standard solution

Question 6

what must a substance be to be considered as a primary standard?

Answer 6

-be avaliable in a high state of purity

-be stable when solid and in solution

-be soluble

-have a reasonably high GFM

Question 7

What are concordant results?

Answer 7

Results within 0.1 cm³ of each other

Question 8

when are back titrations used

Answer 8

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

-when no suitable indicator is avalialbe for a direct titration

-the end-point of the back titration is clearer than

that of the direct titration

-the reaction between the standard reagent and

analyte is slow

-the analyte is insoluble.

Question 9

why is sodium hyrdoxide not a primary standard?

Answer 9

-relatively low gfm
-unstable as a solid (absorbs moisture)
-unstable as a solution
must be standardised before being used in volumetric analysis