Identifying Ions And Functional Groups

Question 1

Group 2 Ion Flame Tests (Ca, Sr, Ba)

Answer 1

Ca - Brick Red
Sr - Red
Ba - Pale Green

Question 2

Group 2 ions plus -OH (Mg, Ca, Sr, Ba)

Answer 2

Mg - slight white ppt
Ca - slight white ppt
Sr - slight white ppt
Ba - colourless solution (no change)

Question 3

Group 2 ions plus excess -OH (Mg, Ca, Sr, Ba)

Answer 3

Mg - White ppt
Ca - Slight white ppt
Sr - Slight white ppt
Ba - Colourless solution (no change)

Question 4

Test for ammonium ion (NH₄⁺)

Answer 4

Add NaOH to neutralise and form water
Gaseous NH₃ turns damp red litmus paper blue when gently heated

Question 5

Test for sulfate ions (SO₄²⁻)

Answer 5

Dilute HCl
BaCl₂
White ppt forms

Question 6

Halide ions (Cl, Br, I)

Answer 6

Dilute HNO₃ and AgNO₃
Cl - white ppt
Br - cream ppt
I - yellow ppt
To check add dilute ammonium solution, Cl dissolves then Br in conc and I won’t dissolve

Question 7

Test for Carbonate Ions (CO₃²⁻)

Answer 7

Add an acid to for carbon dioxide
Bubbling through limewater (calcium carbonate) will turn it cloudy

Question 8

Test for alcohol

Answer 8

Sodium metal
Effervescence

Question 9

Test for tertiary alcohol vs primary and secondary

Answer 9

Acidified potassium dichromate
Orange to Green with primary and second alcohols
Stays orange if tertiary

Question 10

Test for aldehydes and ketones

Answer 10

2cm Fehlings and Benedict’s
5 drops of solution
Heat in water bath
Turn from blue to brick red with aldehydes, no change with ketones

Question 11

Test for Aldehydes/Ketones

Answer 11

Tollens
2cm³ of 0.1moldm⁻³ silver nitrate
A few drops of NaOH to form brown ppt
Add drops of ammonia solution until dissolved
Form a silver mirror with aldehyde but no change with ketone

Question 12

Test for Carboxylic acids

Answer 12

Add sodium carbonate
Effervescence
Bubble through lime water which turns cloudy with carbon dioxide

Question 13

Test for alkenes

Answer 13

2cm³ of sample
2cm³ of bromine water and shake
From orange to colourless