3.6 Organic Analysis

Question 1

How do you test for alkenes? What is the result?

Answer 1

Shake with bromine water, result is bromine water is delocolouised (orange to colourless)

Question 2

How do you test for carboxylic acids? What is the result?

Answer 2

Add Na2CO3 (aq), result: COs (g) given off- effervescence

Question 2

How do you test for halogenoalkanes? What is the result?

Answer 2

Add NaOH (aq) and warm, acidify with HNO3, add AgNO3 (aq)

Result: precipitate of AgX (for CL= white, for Br= cream, for I= yellow)

Question 2

How do you test for alcohols? What is the result?

Answer 2

Question 3

How do you test for aldehydes? What is the result? (2)

Answer 3

1. Warm Fehling’s solution, result: brick red ppt forms (from blue solution)
2. Warm with Tollens’ reagent, result: “silver mirror” (Ag(s) ppt) forms

Question 4

How do you test for carboxylic acids? What is the result?

Answer 4

Add Na2CO3 (aq), result: CO2 (g) given off- effervescence

Question 4

What is mass spectrometry? How does it work?

Answer 4

Question 5

What does the x-axis show on a mass spectrum? What does this effectively show and why?

Answer 5

Shows m/z value (mass divided by ionic charge). Since most ions are 1+, this effectively show Mr

Question 6

Why are there multiple peaks when molecules are put into a mass spectrometer?

Answer 6

The molecular ion is shown as a peak, but it will also FRAGMENT into smaller molecules, so these peaks are shown as well

Also, due to isotopes of atoms, different peaks may be seen

Question 7

How does gas chromatography work and what does it tell you?

Answer 7

A stream of gas carries a mixture of vapours through a column packed with solids, different compounds move through at different speeds, so they are separated. The amount of each compound can then be measured

Question 8

What does GCMS stand for?

Answer 8

Gas chromatography linked to mass spectrometry

Question 8

What might GCMS be used for?

Answer 8

Powerful chemical analysis- forensic work, measure water pollution, drug testing on athletes, racehorses

Question 9

What is high resolution mass spectrometry?

Answer 9

Mass spectrometers which give Mr to 3.d.p or 4.d.p are called high resolution (low resolution is to nearest whole number)

Question 10

What does high resolution mass spec allow you to do?

Answer 10

Distinguish between compounds that have the same Mr to the nearest whole number, but are made up of different atoms and therefore have different values of Mr to 3.d.p

Question 10

What does high resolution mass spec allow you to do ?

Answer 10

Distinguish between compounds that have the same Mr to the nearest whole number, but are made up of different atoms and therefore have different values of Mr to 3.d.p

Question 11

Why do atoms and chemical bonds absorb infrared radiation?

Answer 11

They are constantly vibrating- they can absorb infrared radiation that is the same frequency as their frequency of vibration

Question 12

What effect does a stronger bond have on the frequency of vibration?

Answer 12

Vibrate faster (with higher frequency)

Question 13

What effect do heavier atoms have on the frequency of vibration?

Answer 13

Vibrate slower (with lower frequency)

Question 14

How does infrared spectroscopy work?

Answer 14

Every bond has a unique vibration frequency in the infrared region of the EM spectrum

Bonds absorb radiation that has the same frequency as their frequency of vibration

Infrared radiation emerged from a sample that is missing the frequencies that have been absorbed —> this information can be used to identify the compounds functional group

Question 15

What happens inside an infrared spectrometer?

Answer 15

Beam of infrared radiation with a range of frequencies is passed through the sample

Radiation that emerges is missing frequencies that have been absorbed by the bonds in the sample

Graph is plotted of intensity against frequency of radiation

Question 16

What do the troughs on an infrared spectrum show?

Answer 16

The frequencies where radiation has been absorbed- match to table to find out which bonds they represent

Question 16

What is the fingerprint region?

Answer 16

Question 17

How is the finger print region used to identify compounds?

Answer 17

The fingerprint region’s pattern is matched to a database on a computer to identify the compound accurately