Unit 3-Chemical Analysis

Question 1

What is chromatography used for?

Answer 1

To separate substances in complex mixtures.

Different substances travel at different speeds, so some move further than others in a given time.

Question 2

What factors can affect how far a sample travels?

Answer 2

The size or the polarity of the molecules involved.

Large molecules move slowly whereas smaller molecules are more mobile.

Polar molecules will be more strongly attracted to polar solvents, and so would move further if a polar solvent was used as opposed to a non-polar solvent.

Question 3

What is a standard solution?

Answer 3

A solution of accurately known concentration

Question 4

In a titration what is meant by concordant results?

Answer 4

Volumes within 0·2 cm³ are considered to be concordant at Higher

Question 5

In a titration what is meant by the end point?

Answer 5

The end-point is the point at which the reaction is just complete.

Question 6

In a titration why is an indicator used?

Answer 6

An indicator changes colour showing the end point

Question 7

Describe in detail how a burette should be prepared and set up, ready to begin a titration.

Answer 7

1. Rinse the burette – rinse the burette with the required solution/with the solution to be put in it.
2. Fill burette above the scale with solution
3. Filter funnel used should be removed
4. Tap opened / some solution drained to ensure no air bubbles

Question 8

Why is an indicator not required for some redox titrations such as ones using potassium permanganate?

Answer 8

Potassium permanganate is coloured and loses colour when it is reduced.