3.6 - Organic Analysis

Question 1

What does the Position of each Inverted Peak/Absorption show?

Answer 1

Which bonds are present & ∴ which functional groups are present in organic compound

Question 2

What are Fragment ions?

Answer 2

Ions caused by Break up of unstable Molecular ion

Question 3

What is the Fingerprint Region?

Answer 3

Region below 1500cm⁻¹ which is unique to a compound

Computer compared this to database ∴ identifying the compound

Question 4

What is an I-R spectrum?

Answer 4

A graph of % transmittance against wave number (cm⁻¹)

Question 5

What is Wavenumber proportional to?

Answer 5

Frequency

Question 6

What can the results of the Combustion of organic substances be used to determine?

Answer 6

Empirical Formula of Compound

Question 7

What is Infra-red Spectroscopy?

Answer 7

Analytical technique used to Identify types of Organic compounds

Question 8

Why is there sometimes a Small Peak above Molecular ion Peak?

Answer 8

Presence of Carbon-13 Isotope

Question 9

When is High res mass spectrometry useful?

Answer 9

When compounds have the same whole no. Mr

e.g. propan-1-ol & ethanoic acid

Question 10

Three main Greenhouse gases?

Answer 10

CO₂
CH₄
H₂O

Question 11

Easy to Identify Characteristic of O-H peaks?

Answer 11

Smooth Peak

Question 12

Test for Aldehydes?

Answer 12

Tollens’ - Silver Mirror
Acidified Potassium Dichromate - Orange |> Green
Fehling’s - Blue Solution |> Brick Red ppt.

Question 13

How do you calculate Empirical Formula?

Answer 13

Mass
Ar
moles
Simplest Ratio

Question 14

Between CO₂ & H₂O, which absorbs & re-emits more

I-R radiation?

Answer 14

H₂O as O-H peak has larger absorption area

Question 15

Test for Carboxylic Acids?

Answer 15

Na₂CO₃ - fizz (CO₂)

Universal indicator - red/orange

Question 16

Test for Alkenes?

Answer 16

Decolourises Bromine Water

Question 17

How many decimal places can a High-res Mass Spectrometer measure Ar & Mr to?

Answer 17

4

Question 18

When are Fingerprint regions most Useful?

Answer 18

When the same bonds are present in the compounds analysed

Question 19

Why do CO₂, CH₄ & H₂O absorb infrared radiation?

Answer 19

Contain C=O
O-H or
C-H bonds

Question 20

Test for Primary & Secondary Alcohols?

Answer 20

Acidified Potassium Dichromate
H⁺/Cr₂O₇²⁻
Orange |> Green

Question 21

Define: Molecular ion Peak

Answer 21

Line w/ largest m/z (mass to charge) ratio, giving Mr of compound

Question 22

Test for Tertiary Alcohols?

Answer 22

Acidified Potassium Dichromate
H⁺/Cr₂O₇²⁻
No Visible change

Question 23

What are the lines on a Mass Spectrum due to?

Answer 23

Fragment ions
&
Molecular ion

Question 24

What is Infra-red Spectroscopy used for?

Answer 24

|> To detect presence of specific covalent bonds in a compound
|> Each type of bond vibrates at specific frequency & so absorbs specific frequency of I-R radiation

Question 25

How do you calculate Empirical Formula from masses of CO₂ & H₂O after combustion of CxHyOz in excess oxygen?

Answer 25

|> Calculate moles of CO₂ & H₂O
|> Calculate moles of C (same as CO₂)
|> Calculate moles of H (moles of H₂O x 2)

|> Calculate mass of C (x12)
|> Calculate mass of H (x1)

|> Calculate mass of O

|> Calculate Empirical Formula from: masses, Ar, moles, then Simplest Ratio

Question 26

Test for Halogenoalkanes?

Answer 26

AgNO₃

Cl⁻ - white ppt
Br⁻ - cream ppt
I⁻ - yellow ppt

Question 27

Alcohols react with Sodium to form ____ ?

Answer 27

Salt & Hydrogen