Standard Solutions

Question 1

Define a standard solution

Answer 1

A standard solution is a solution whose concentration is accurately known

Question 2

How is a standard solution prepared?

Answer 2

By dissolving a definite, precisely known mass of solute in a suitable solvent to give a definite, precisely known volume of solution

Question 3

Why or why not is it possible to weigh out a precise quantity of sulfuric acid?

Answer 3

It is not possible as it absorbs moisture from the air

Question 4

Name all of the criteria a substance must meet to be classified as a primary standard (6)

Answer 4

1. It must be available in a highly pure state.
2. It must be stable in air, e.g. it should not lose water of crystallisation to the air (efflorescence) or absorb water from the air (be deliquescent or hygroscopic).
3. It must dissolve easily in water.
4. It should have a fairly high relative molecular mass (so that the precision in weighing out a known mass is as high as possible).
5. When used in volumetric analysis, it should undergo complete and rapid reaction.
6. It should not be hydrated, i.e. it must be anhydrous (have no water of crystallisation).

Question 5

What is efflorescence

Answer 5

When a substance loses water of crystallisation to the air is known as efflorescence

Question 6

Define primary standard

Answer 6

A primary standard is a substance that can be obtained in a stable, pure and soluble solid form so that it can be weighed out and dissolved in water to give a solution of accurately known concentration.

Question 7

Give some examples of primary standards

Answer 7

anhydrous sodium carbonate, sodium chloride, potassium dichromate,