3.6: Organic analysis

Question 1

State the chemical test for alkenes

Answer 1

• add bromine water
• orange to colourless colour change

Question 2

State the chemical test for primary and secondary alcohols

Answer 2

• warm with acidified potassium dichromate
• orange to green colour change

Question 3

State the chemical test for tertiary alcohols

Answer 3

• warm with acidified potassium dichromate
• no visible change

Question 4

State both of the chemical tests for aldehydes

Answer 4

• warm with Tollen’s reagent
• forms a silver mirror
• warm with Fehling’s solution
• forms a brick red precipitate

Question 5

State the chemical test for carboxylic acids

Answer 5

• add sodium carbonate
• effervescence

Question 6

State the chemical test for halogenoalkanes

Answer 6

• warm with aqueous silver nitrate
• precipitate forms (Cl - white ppt, Br - cream ppt, I - yellow ppt)

Question 7

Write an example equation for ethanol in an alkene test

Answer 7

C2H4 + Br2 -> CH2BrCH2Br

Question 8

Write a general equation for the reaction between an alcohol and sodium

Answer 8

R-OH + Na -> RONa + 1/2H2

Question 9

Write a pair of general equations for the reactions between a primary and a secondary alcohol with acidified potassium dichromate

Answer 9

• primary: RCH2OH + [O] -> RCHO
• secondary: RCHOHR1 + [O] -> RCOR1

Question 10

Write a general equation for the reaction between an aldehyde and Fehling’s solution

Answer 10

RCOH + [O] -> RCOOH

Question 11

Give an example of an ionic equation for the reaction between an aldehyde and Fehling’s solution

Answer 11

2CU(2+)(aq) + 2OH(-)(aq) +2e(-) -> Cu2O(s) + H2O (l)

Question 12

Write a general equation for the reaction between an aldehyde and Tollen’s reagent

Answer 12

RCOH + [O] -> RCOOH

Question 13

Give an example of an ionic equation for the reaction between an aldehyde and Tollen’s reagent

Answer 13

Ag(+)(aq) + e(-) -> Ag(s)

Question 14

State the general equation for the chemical test for carboxylic acids

Answer 14

2RCOOH + Na2CO3 -> 2RCOO(-)Na(+) + H2O + CO2

Question 15

State the general formula for the chemical test for halogenoalkanes

Answer 15

RX + NaOH -> ROH + Na(+) + X(-)

Question 16

Give an ionic equation for the reaction that occurs during a halogenoalkane test

Answer 16

Ag(+)(aq) + X(-)(aq) -> AgX(s)

Question 17

What is an infrared spectrum a graph of?

Answer 17

% transmittance against wave number (cm^-1)

Question 18

What is the fingerprint region?

Answer 18

The region below 1500(cm^-1). A computer can compare the fingerprint region to a database to identify the compound.

Question 19

Where would you expect to find peaks in the infra-red spectrum or butanoic acid?

Answer 19

O-H absorption between 3230-3550(cm^-1)
C=O absorption between 1680-1750(cm^-1)