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A Level Chemistry > Chapter 17 - Spetroscopy > Flashcards

Chapter 17 - Spetroscopy Flashcards

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1
Q

When an organic compound is placed inside the mass spectrometer, what happens?

A

It loses an electron and forms a positive ion, which is called the molecular ion

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2
Q

How to find the molecular ion?

A

It will be the largest peak furthest to the right

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3
Q

What is the M+1 peak?

A

A very small peak after the molecular ion on the spectrometer

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4
Q

Why is the M+1 peak formed?

A

Isotopes - normally due to the carbon-13 isotope

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5
Q

What is fragmentation?

A

The process in which the molecular ion is broken down into smaller fragments

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6
Q

What are the smaller peaks on a spectrometer caused by?

A

Fragments

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7
Q

What two things are produced when a molecular ion is fragmented?

A

A positively charged ion and a free radical

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8
Q

Out of the two things produced by fragmentation, which will be detected by the spectrometer?

A

The positively charged ion

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9
Q

What does the unit m/z show?

A

It is a ration of mass to charge

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10
Q

How is it possible to tell two compounds with the same Mr apart using mass spectrometry?

A

They have different structures so won’t produce the same fragments, which will be seen on the spectrum

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11
Q

How to combine spectrometry techniques to work out a compound

A

1) Use the composition to work out the molecular mass of the compound
2) Work out what functional groups are in the compound from its infrared spectrum
3) Use the mass spectrum to work out the structure of the molecule

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12
Q

What is the m/z value of CH3+ ion?

A

15

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13
Q

What is the m/z value of a C2H5+ ion?

A

29

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14
Q

What is the m/z value of a C3H7+ ion?

A

43

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15
Q

What is the m/z value of a C4H9+ ion?

A

57

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16
Q

How to calculate the number of carbon atoms in a compound using the spectrum?

A

(Height of M+1 peak/height of M peak) x 100

17
Q

What are the two ways in which a bond can move?

A

It can bend or it can stretch

18
Q

What happens when a bond absorbs infrared radiation?

A

They bend or stretch more

19
Q

What happens when a stretch occurs?

A

The distance between the two atomic centres increase and decrease

20
Q

What happens when a stretch occurs?

A

The bond angle changes

21
Q

What does the amount that a bond stretches or bends depend upon?

A

The mass of atoms in the bond

The strength of a bond

22
Q

Will stronger bonds vibrate more or less?

A

More

23
Q

When will a bond absorb infrared radiation?

A

When it has the same frequency as the bonds in the molecule

24
Q

What can infrared spectroscopy be used for?

A

Identifying different functional groups because they absorb different frequencies of infrared radiation

25
Q

The process of infrared spectroscopy

A

The sample is placed inside an infrared spectrometer
A beam of IR radiation is passed through the sample
The molecule absorbs some of the IR frequencies and the emerging beam is analysed to work out what frequencies these are
A computer then plots transmission against wavenumber

26
Q

What is the fingerprint region?

A

Unique peaks that can be used to identify the molecule

27
Q

From an infrared spectrum, how do you identify the different functional groups?

A

Compare the frequencies against the ones found in the data table

28
Q

What will all organic compounds produce on a spectrum?

A

A peak between 2850 and 3100 from the C-H bond

29
Q

What are the three functional groups you should be able to identify from a spectrum?

A

O-H group in alcohols
C=O group in aldehydes, ketones and carboxylic acids
COOH group in carboxylic acids

30
Q

What will the spectrum of an alcohol show?

A

A peak between 3200 and 3600 because of the O-H group

31
Q

What will the spectrum of an aldehyde or ketone show?

A

A peak between 1630 and 1820 because of the C=O bond

32
Q

What will the spectrum of a carboxylic acid show?

A

A peak at between 1630 and 1820 caused by the C=O bond

A broad peak between 2500 - 3300 caused by the O-H group

33
Q

Main use of infrared spectroscopy

A

Breathalysers

34
Q

Why can infrared spectroscopy be used in breathalysers?

A

The intensity of the peaks of bonds associated with ethanol, e.g. C-H

35
Q

Why is infrared spectroscopy used to monitor the concentrations of polluting gases?

A

Peaks associated with the bonds found in the pollutants can be measured for intensity

36
Q

What is elemental analysis?

A

Use of percentage composition data to determine the empirical formula

37
Q

What is mass spectrometry?

A

Use of a molecular ion from a spectrum to determine the molecular mass

38
Q

What is infrared spectroscopy?

A

Use of absorption peaks from a spectrum to identify bonds and functional groups that are present

A Level Chemistry (29 decks)

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