organic analysis

Question 1

to identify whether our substance contains an alkene functional group we use

Answer 1

bromine solution

we put a sample of our test in a test tube
and add a few drops of bromine solution
bromine solution is brownish reddish

it changes from brownish to colourless if C=C are present (alkenes functional group)

Question 2

We can test whether we have a tertiary alcohol using

Answer 2

H+ / K2Cr2O7 (acidified potassium dichromate)

if we add it to our sample and our solution remains orange we have tertiary
if it changes to green we have a primary and secondary alcohol present

Question 3

what is the test identify primary or secondary alcohol

Answer 3

we add tollens reagent
if we have a primary = aldehyde it turns into a silver mirror
if it’s colourless it’s secondary alcohol =ketone

Question 4

name the reagent you could add to a solution to test for the presence of ethanolic acid

Answer 4

carbonate or magnesium

Question 5

name a reagent you could add to a solution to test for presence of ethene

Question 6

Name the reagent you could add to a solution to test for the presence of 2-ethylhexan-2-ol or 2-ethylhexan-1-ol

Answer 6

acidified potassium dichromate

Question 7

Acidified potassium dichromate is added to a solution containing either propan-1-ol or propan-2-ol.

Name a reagent you could add to the resulting solution to test if the original alcohol is propan-1-ol or propan-2-ol.

Answer 7

tollens reagent / benedict’s solution

Question 8

name a reagent you could add to a solution to test for the presence of hex-3-ene

Answer 8

bromine solution

Question 9

name a reagent you could add to a solution to test for the presence of formaldehyde

Answer 9

tollens reagent

Question 10

Name a reagent you could add to a solution to test for the presence of 3-methylpentanoic acid

Answer 10

carbonate or magnesium

Question 11

chemist has discovered that the labels have fallen off four bottles each of which contains a different organic liquid. These liquids are known to be butanal, butanoic acid, butan-1-ol and 1-bromobutane.
Suggest a series of 3 test-tube reactions which could be used to determine which compound is in which bottle.
For each test, state the reagents used and the observations expected.
[6 marks]

Answer 11

If the solution is a primary alcohol we add tollens reagent to find that which will turn it into a silver precipitate which indicates it’s butanal

if there’s no colour present it’s another molecule. We then add acidified potassium dichromate, if there’s a secondary or primary alcohol present it will turn green so it’s butan-1-ol but if it’s colourless it’s another molecule.
we then add sodium carbonate to the solution. if its giving bubbles then it’s a carboxylic group ( butanoic acid) if not it’s 1-bromobutane

Question 12

What would you add to a solution to distinguish between propan-2-ol and methylpropan-2-ol

what would happen if we add this to propan-2-ol and 2-methylpropan-2-ol?

Answer 12

acidified / H+
potassium dichromate

if we add it to propan-2-ol it will turn green
if we add it to 2-methylpropan-2-ol there’s no change it will remain orange

Question 13

Calculate the masses of propanone and butanone to 5 decimal places, using the relative isotopic mass data below. You can assume that no other isotopes are present

Hydrogen-1: 1.00783
Carbon-12: 12.00000
Oxygen-16: 15.99491

Answer 13

Propanone= (3x 12.00000) + (6x 1.00783) + (1x 15.99491) = 58.04189

butane = (4x 12.00000) + (10x 1.00783) = 58.07830

Question 14

What is the general formula of methyl propane’s

Answer 14

C4H10

Question 15

What is fragmentation

Answer 15

when molecular ions split into 2 or more parts called fragments

Question 16

fragmentation is especially likely when the ionisation method is

Answer 16

electron impact as it makes fragmentation occur more likely

Question 17

What do these lines tell us about

Answer 17

the molecules structure

Question 18

What are the fragments to look for for this molecule?

Answer 18

it can divide into 3
CH3+ = m/z 15
C2H5+ = m/z 29
C3H7+ = m/z 43

Question 19

Explain what the method is for chromatography

Answer 19

1) start with piece of glass, plastic or metal coat it with a thin layer or silica (SiO2) or aluminia (Al2O3) which is called coated sheet
2) draw a pencil line near the bottom of the plate and add a small drop of a sample then place a plate into the beaker containing a solvent. There should be enough to cover bottom of there coated sheet but it shouldn’t touch the line

4) then cover the solvent and wait for it to rise the coating then is soaked by the solvent causing it to rise and seperate into 3 dots whilst it rises

Question 20

What’s the solvent that moves the component called?

Answer 20

moving phase

Question 21

what’s the thing that moves through the coated sheet

Answer 21

stationary phase

Question 22

Ethanol could form hydrogen bonds to the stationary phase (silica gel)
Therefore, ethanol adsorbs strongly to the stationary phase.
As a result, retention of ethanol by the stationary phase is

Answer 22

high

because hydrogen bonds can form between them

Question 23

the distance a component moves can be partly explained by

Answer 23

by the level of retention of the component by the stationary phase and whether the component and the stationary phase are both polar or could form hydrogen bonds

Question 24

Retention will be high if

Answer 24

both component and stationary phase are polar or if hydrogen bonds can form between them