3.6 Organic Analysis

Question 1

Give the definition of a molecular ion.

Answer 1

A molecular ion is the molecule with one electron knocked off (it is both and ion and a free radical)

Question 2

What can be used to determine the molecular formula of a compound?

Answer 2

High resolution mass spectrometry can be used to determine the molecular formula of a compound from the accurate mass of the molecular ion.

Question 3

To what decimal place can high resolution mass spectrometry measure mass to?

Answer 3

5 d.p.

This can help differentiate between compounds that appear to have similar Mr (to the nearest whole number)

Question 4

Answer the example question 1 on page 1 in the chemrevise revision guide.

Answer 4

correct?

Question 5

How many molecular ion peaks will occur if a compound contains a chlorine or a bromine atom?

What type of peaks?

Why?

Answer 5

2 peaks

a M and a M+2 peak

Due to the two naturally occurring isotopes of chlorine or bromine.

Question 6

What are the two naturally occurring isotopes of chlorine?

Answer 6

Cl35 (75%)

Cl37 (25%)

Question 7

What are the two naturally occurring isotopes of bromine?

Answer 7

Br79 (50%)

Br81 (50%)

Question 8

What will the m/z value be for CH3Cl35 and CH3Cl37?

What will the ratio of heights be?

Answer 8

CH3Cl35 - 50

CH3Cl37 - 52

3:1

(see page 1 in the chemrevise revision guide)

Question 9

What will the m/z value be for CH3Br79 and CH3Br81?

Answer 9

CH3Br79 - 94

CH3Br81 - 96

1:1

(see page 1 in the chemrevise revision guide)

Question 10

Read the box labelled 1 on page 1 in the chemrevise revision guide.

Answer 10

understand?

Question 11

Read the box labelled 1 on page 2 in the chemrevise revision guide.

Answer 11

understand?

Question 12

In an infrared spectra, what is the information above 1500cm-1 and what is the information below 1500cm-1?

Answer 12

Above - functional group identification

Below - fingerprinting

Question 13

Look at the graph in on page 2 in the chemrevise revision guide, give the two functional groups shown there using the IR absorption table below.

Answer 13

answer is below table, correct?

Question 14

need to do work on infrared spectroscopy

Answer 14

feel confident you know it?

Question 15

Read the top of page 3 in the chemrevise revision guide

Answer 15

understand?

Question 16

In a test tube reaction, what reagent is used to test for alkenes?

What is the result if positive?

Answer 16

Bromine water

Orange colour -> colourless

Question 17

In a test tube reaction, what reagent is used to test for aldehydes?

What is another reagent used?

What is the result if positive?

Answer 17

Fehling’s solution

Blue solution -> red precipitate

Tollen’s reagent

Silver mirror formed

Question 18

In a test tube reaction, what reagent is used to test for Carboxylic acids?

What is the result if positive?

Answer 18

Sodium carbonate

Effervescence of CO2 evolved

Question 19

In a test tube reaction, what reagent is used to test for 1º 2º alcohol and aldehyde?

What is the result if positive?

Answer 19

Sodium dichromate and sulfuric acid

Orange -> green

Question 20

In a test tube reaction, what reagent is used to test for chloroalkanes?

What is the result if positive?

Answer 20

Warm with silver nitrate

Slow formation of white precipitate of AgCl

Question 21

For Tollen’s reagent with aldehydes:

How is the reagent formed?

What are the conditions?

What is the reaction?

What are the observations?

Answer 21

(see page 3 in the chemrevise revision guide)

Question 22

For Fehling’s solution with aldehydes:

What is the reagent?

What are the conditions?

What is the reaction?

What are the observations?

Answer 22

(see page 3 in the chemrevise revision guide)

Question 23

Draw an equation for the test for the presence of a carboxylic acid.

Answer 23

(see page 3 in the chemrevise revision guide)