3.3.6.1 Identification of functional groups by test-tube reactions Flashcards Preview

AQA A Level Chemistry > 3.3.6.1 Identification of functional groups by test-tube reactions > Flashcards

Flashcards in 3.3.6.1 Identification of functional groups by test-tube reactions Deck (6)
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1
Q

How do you test for alkenes?

A

Shake with bromine water, turns from orange to colourless

2
Q

What is the test for alcohols?

A

Add acidified K2Cr2O7: orange colour turns green with primary or secondary alcohols (also with aldehydes)
Add sodium metal: sodium replaces the hydrogen in the functional group to form hydrogen gas, effervescence

3
Q

What is the test for aldehydes?

A

Warm with Fehling’s solution: blue colour turns to red precipitate
Warm with Tollens’ solution: silver mirror forms

4
Q

What is the test for carboxylic acids?

A
Compound is acidic
Add NaHCO3 (aq): CO2 is given off, bubbles formed
5
Q

How does the Fehling’s test work?

A

Fehling’s reagent is a gentle oxidising agent
It contains blue copper (II) complex ions which oxidises aldehydes but not ketones
During the oxidation the blue copper (II) ions change to a precipitate of red copper (I) ions

6
Q

How does the test for carboxylic acids work?

A

R - COOH + NaHCO3 = R - COONa + H2O + CO2

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