unit 4 - how to pass: standard solutions and dilutions

Question 1

How can standard solutions be prepared?

Answer 1

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 2

What must a primary standard be?

Answer 2

Available in a high state of purity, be stable when solid and in solution, be soluble and have reasonably high GFM.

Question 3

What do examples of primary standards include?

Answer 3

Sodium carbonate, hydrated oxalic acid, potassium hydrogen phthalate, silver nitrate, potassium iodate and potassium dichromate.

Question 4

Why isn’t sodium hydroxide a primary standard?

Answer 4

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

Question 5

What must happen to sodium hydroxide solution before it can be used in volumetric analysis?

Answer 5

It must be standardised.

Question 6

How do you calculate the dilution factor?

Answer 6

dilution factor = total volume after dilution / initial volume added

Question 7

What happens when a concentrated solution is diluted?

Answer 7

The amount of solute does not change, only the amount of solvent.