unit 2b: instrumental analysis

Question 1

empirical formula

Answer 1

the simplest whole number ratio of the elements found in the compound

Question 2

elemental analysis is used to

Answer 2

determine the empirical formula of a compound containing C, H, O, N, and/ or S

Question 3

elemental analysis

Answer 3

a known mass of the compound is burned in excess oxygen, a mixture of gasses is produced, then the mass of each product gas is determined

Question 4

mass spectrometry

Answer 4

a technique used to analyse the mass and potential fragments of a molecule, this can tell you about structures within the molecule

Question 5

parent ion

Answer 5

the peak with the highest m/z, this tells you the gfm of the compound

Question 6

infrared spectroscopy is used to

Answer 6

identify certain functional groups in a compound

Question 7

in an IR-spectrometer

Answer 7

IR radiation is passed through a sample of the compound, depending on the types of bonds present and the atoms, different wavelengths of the radiation are absorbed, the detector measures the intensity of radiation absorbed at different wavelengths

Question 8

the absorbance of infrared radiation is measured in

Answer 8

wave numbers (cm-1)

Question 9

infrared radiation causes

Answer 9

parts of a molecule to vibrate, there are several different types

Question 10

different vibrations

Answer 10

absorb different wavelengths of infrared radiation

Question 11

the wavelength of IR absorbed depends on

Answer 11

the strength of the bond, the type of atoms which are attached to the bond

Question 12

the fingerprint region

Answer 12

the area below 1500cm-1, it is hard to assign peaks here, everything above this can be assigned to a functional group present

Question 13

proton NMR

Answer 13

gives us information about the different chemical environments of hydrogen atoms and how many hydrogen atoms are in each of these compounds

Question 14

NMR uses

Answer 14

radio waves to push the hydrogen atoms to the higher energy state and a detector detects how much energy is released when they relax back down to the low energy stste

Question 15

the amount of energy released in NMR is affected by

Answer 15

the environment of the hydrogen atoms

Question 16

absorptions by the sample are measured against

Answer 16

the absorption of a reference substance

Question 17

the standard reference

Answer 17

TMS, it only has one proton environment and it’s absorption has a chemical shift value of 0 ppm

Question 18

spectra can be obtained using

Answer 18

low resolution or high resolution H NMR

Question 19

low resolution H NMR

Answer 19

shows the number of environments that hydrogen is found in, the chemical environment of the hydrogens, and the number of hydrogens at each environment

Question 20

high resolution H NMR

Answer 20

uses higher radio frequencies than low resolution and produces more detailed spectra, allowing us to tell how many hydrogen neighbours that environment has

Question 21

doublet

Answer 21

1 H atom on the adjacent C, 2 peaks in spectrum

Question 22

triplet

Answer 22

2 H atoms in the adjacent C, 3 peaks in spectrum

Question 23

quartet

Answer 23

3 H atoms in the adjacent C, 4 peaks in spectrum

Question 24

molecular ion

Answer 24

the highest mass ion

Question 25

how could you use NMR to differ between chemicals

Answer 25

different number of peaks

Question 26

relative intensity

Answer 26

the number of H atoms in group