Chapter Ten : Analysis of Organic Compounds

Question 1

Mass spectroscopy

Answer 1

Analyses ions formed from atom and molecules to determine mass/charge
Molecules are bombarded with high energy electrons which are passed through magnetic field producing fragments
Base peak - The most abundant ion at 100%
Parent ion - The highest peak

Question 2

Infrared spectroscopy

Answer 2

Identifies functional groups and bonds in molecules
Graph measures transmittance
Graph peaks when energy is absorbed
Fingerprint region - below 1000cm-1, small crowded peaks that don’t help identify functional groups

Question 3

C13 NMR

Answer 3

Analyses C environments in molecules
No of C environments = no of peaks
TMS = tetramethylsilane, reference point for NMR

Question 4

1H NMR

Answer 4

Shows unique H environments
Ratio shows no of H atoms
n+1 rule gives no of H on neighbouring C atom
If there is a high electronegativity the peak will be further from 0

Question 5

Chromotography

Answer 5

Mobile phase passes through a stationary phase
The components stick then unstick, larger molecules take longer
Adsorption - the adhesion of atoms, ions or moleculesto the stationary phase
Desorption- The removal of a substance from a surface

Question 6

Stationary phase

Answer 6

Solid with a high surface area or finely divided solid coated in liquid

Question 7

Mobile phase

Answer 7

Liquid or gas that flows through chromatography system

Question 8

High performance liquid chromotography HPLC

Answer 8

Stationary phase is a narrow diameter tube, tightly packed with finely divided powder
Eluent is pumped through it
Gives a graph with retention time
Gives a graph w peak area and concentration
Instruments must be calibrated

Question 9

Important features of HPLC graph

Answer 9

Position of its peaks - gives retention time

Area under each peak - The more area the more of that substance

Question 10

Standard solution

Answer 10

Is one whose concentration is accurately known through;

1. Standardisation - by reacting it with another solution whose conc.is accurately known
2. Taking a primary standard and dissolving it in water

Question 11

Primary standard qualifications

Answer 11

Have a high state of purity
Accurately known formula
High stability
Cheap and readily available
High molecular mass

Question 12

Rinsing water left in burette

Answer 12

Burette - underestimated
Titration flask - overestimated
Comment- Burette solution is diluted so more is used

Question 13

Rinsing water left in the pipette

Answer 13

Burette - overestimated
Titration flask - underestimated
Comment - aliquot is diluted

Question 14

Indicator chosen changes too soon

Answer 14

Burette - overestimated
Titration flask - underestimate
Comment - indicator choice is critical

Question 15

Water in titration flask

Answer 15

Burette - no effect
Titration flask - no effect
Comment - all necessary measurements are made prior to chemicals mixed with the water

Question 16

Concentration of standard solution lower than calculated

Answer 16

Burette - overestimated
Titration flask - overestimated
Comment - few moles of syandard solution will be used, substance analysed will appear ot have a higher concentration

Question 17

Concetration of standard solution higher than calculated

Answer 17

Burette -underestimated
Titration flask - underestimated
Comment - more moles of st sol will be used; substance analysed will appear to have a lower concentration

Question 18

Random errors

Answer 18

Burette - variable
Titration flask - variable
Comment - can be minimised by repitition