PAG 7 - Qualitative analysis of organic functional groups

Question 1

What reagent is used to test for the

presence of an alkene?

Answer 1

Bromine water

Question 2

What is observed when bromine water is

added to an alkene?

Answer 2

The solution will change from orange to

colourless

Question 3

What is observed when bromine water is

added to a saturated hydrocarbon?

Answer 3

The solution remains orange

Question 4

Briefly describe how to test for

haloalkanes

Answer 4

Add silver nitrate solution to an aqueous solution of a halide and observe the colour
of any precipitate formed

Question 5

What colour precipitate forms when
silver nitrate solution reacts with chloride
ions?

Answer 5

White

Question 6

What colour precipitate forms when
silver nitrate solution reacts with bromide
ions?

Answer 6

Cream

Question 7

What colour precipitate forms when
silver nitrate solution reacts with iodide
ions?

Answer 7

Yellow

Question 8

Describe the solubilities of the silver
halide precipitates in dilute and
concentrated ammonia

Answer 8

AgCl - soluble in dilute and concentrated
ammonia
AgBr - soluble in concentrated ammonia
AgI - insoluble in ammonia

Question 9

Briefly describe how to test for carboxylic

acids

Answer 9

Add some sodium carbonate solution to the sample. If
a carboxylic acid is present, there will be
effervescence and CO2
will be produced.
To test the gas, bubble it through limewater. CO2
willcause the limewater to turn cloudy

Question 10

What reagent can be used to test for the

presence of an alcohol?

Answer 10

Acidified potassium dichromate solution

Question 11

What is observed when a primary or
secondary alcohol is heated under reflux
with acidified potassium dichromate
solution?

Answer 11

There is a colour change from orange to

green

Question 12

What is observed when a tertiary alcohol
is heated under reflux with acidified
potassium dichromate solution?

Answer 12

No colour change - solution remains

orange

Question 13

What 2 reagents can be used to
distinguish between an aldehyde and a
ketone?

Answer 13

1. Fehling’s solution

2. Tollens’ solution

Question 14

What is observed when Fehling’s
reagent is heated with:
a) An aldehyde?
b) A ketone?

Answer 14

a) Brick red precipitate forms
b) No precipitate forms, solution remains
a deep blue colour

Question 15

What is observed when Tollens’ solution
is heated with:
a) An aldehyde?
b) A ketone?

Answer 15

a) Silver mirror forms on the surface of
the test tube
b) No change observed

Question 16

What is Brady’s reagent used to identify?

Describe the positive result for this test

Answer 16

Used to identify carbonyls (aldehydes or
ketones).
A yellow-orange precipitate forms in the
presence of a carbonyl.

Question 17

Briefly describe the test for phenol and

the positive result for this test

Answer 17

Add bromine water.
If phenol is present, the solution will
change from orange to colourless and a
white precipitate will form.

Question 18

When would a water bath or electric
heater be used instead of a Bunsen
burner to heat a sample?

Answer 18

• When the temperature needs to be
  controlled more
• When the chemicals being heated are
  highly flammable