3.8 Instrumental Analysis

Question 1

Name 3 disadvantages to using chemical analysis methods for identifying chemicals

Answer 1

• expensive
• needs specialist training as it’s very complex
• requires expert analysis and comparison

Question 2

Name 3 advantages to using chemical analysis methods for identifying chemicals

Answer 2

• quick
• only need tiny samples
• accurate and sensitive

Question 3

What do samples that need to be identified often have to do before?

Answer 3

Be separated so each substance can be identified

Question 4

Name a way gases can be separated

Answer 4

Gas chromatography

Question 5

Name a way gases can be identified

Answer 5

Mass spectrometer

Question 6

What is the retention time?

Answer 6

The time it takes for a component in a mixture to pass through the column

Question 7

How does gas chromatography work?

Answer 7

It separates different parts of the mixture into their compounds as they have different retention times so they come out of the gas chromatography column at different times as they travel at different speeds. The retention times of the compounds can be compared to those of the known compounds so we can identify the compounds in the mixture

Question 8

How does mass spectrometry work?

Answer 8

Samples of the compound are injected and ionised in the machine. There is a electromagnetic field which ensures all ions have the same kinetic energy. The magnetic field deflects the positive ions because they curve towards the negative side of the magnetic field. The length to which they curve helps identify the compounds

Question 9

What is the molecular ion peak?

Answer 9

The most likely relative formula mass for that compound

Question 10

Where can you find the molecular ion peak on a graph?

Answer 10

It’s the one to the right on a mass spectrum