analytical techniques

Question 1

what is the environment of an atom

Answer 1

it depends on the surrounding atoms and bonds in the molecule

Question 2

what is infrared spectroscopy

Answer 2

uses infrared radiation to increase the vibrational energy of covalent bonds in a sample

Question 3

what are two things affecting the frequency of infrared radiation absorbed by a covalent bond

Answer 3

-atoms on either side of bond
-position of bond in a molecule

Question 4

what is mass spectrometry used for

Answer 4

finding the relative molecular mass of a compound (Mr)

Question 5

what is fragmentation in mass spectrometry

Answer 5

molecules break up when they are bombarded with high energy electron

Question 6

what is resonance

Answer 6

nuclei exhibit overall spin, and can flip their spin alignment up or down

Question 7

why is TMS used in NMR

Answer 7

used for reference to compare peaks to as it has a chemical shift of 0
it is unreactive

Question 8

why does TMS only produce one peak

Answer 8

all the hydrogen atoms are equivalent in molecule

Question 9

what is used as the stationary phase in thin layer chromatography

Answer 9

silicon oxide or aluminium oxide powder than substance can adsorb to (polar)

Question 10

equation for Rf value

Answer 10

distance travelled by substance / distance travelled by solvent

Question 11

what would change the Rf value of a substance

Answer 11

different stationary / mobile phase

Question 12

steps for column chromatography

Answer 12

-sample dissolved in solvent and put at top of column
-tap opened and more solvent added on top
-as solvent passes through column the components of mixture begin to seperate

Question 13

advantage of column chromatography over thin layer chromatography

Answer 13

much larger quantities can be seperated

Question 14

what is the equivalent to Rf for gas chromatography

Answer 14

retention time - time taken for substance to pass from column inlet to detector

Question 15

why is there sometimes a tiny peak at m/z +1 on mass spec of organic compounds

Answer 15

carbon 13 isotope

Question 16

how does infrared spectroscopy work

Answer 16

-multiple frequencies of infrared passed through a sample
-bonds absorb some frequencies, others are transmitted
-frequencies that pass through are NOT absorbed by bonds
-instrument plots a graph of transmittance

Question 17

what does OH and COOH resemble on infrared spec

Answer 17

big trough at 3200-3400
COOH - spiky trough

Question 18

what does C double bond O resemble on infrared spec

Answer 18

sword peak at around 1700