1.10 Qualitative Tests

what are two ways to desribe solid

crystaline (can see crystals) or powder (cant)

what are white solids

could contain group 1 or 2 ion

does not contain transition metal ions however

could contian Ag⁺, Zn^2-, Al³⁺, NH₄^-

coloured ions

contain transition metal ion

Cu²⁺ typically blue,

Fe²⁺ green

Fe³⁺ brown

Flame test

1. Ensure nichrome wire is clean (dip in concentrated hydrochloric acid in blue Bunsen burner flame until no impurities are detected).

1. Dip the nichrome wire into concentrated hydrochloric acid.

2. Dip the wire into the test solid.

3. Hold the wire in a blue Bunsen burner flame.

4. Note the colour of the flame.

Why is nichrome wire used

It’s inert does not react with sample and high melting point

Sodium ion Na⁺ flame test

yellow/orange

barium ion Ba²⁺ flame test

green/apple green

Copper ion Cu²⁺ , flame test

green-blue/blue green

lithium ion Li⁺ flame test

crimson

calcium ion Ca²⁺ flame test

brick red

potassium ion K,⁺ flame test

lilac but pink through a cobalt blue filter

test for carbon dioxide 

turns limewater (calcium hydroxide solution) colourless to milky/cloudy. If excess CO2 is bubble through the precipitate dissolves to give a colourless solution

Hydrogen test

Use a burning splint and it gives a squeaky pop

Oxygen test

relights a glowing splint

hydrogen chloride test

gives white fumes with ammonia 

also turns moist universal indicator paper red (in fume cupboard)

ammonia test

turns moist universal indicator blue (basic gas)

gives white fumes with concentrated hydrogen chloride

chlorine test

turns damp litmus/universal indicator paper red then bleaches white 

Iodine (I₂) Test method and results

Test the sample with 2-3 drops of starch solution. Blue-black solution formed

Sulfate test method

1. If solid first make solution of salt e.g spatula measure in a test tube half filled with deionised water

2. add 1cm³ of barium chloride solution (acidified with nitric acid)

sulfate test result

white precipitate: sulfate ion SO₄^-2 present

no precipitate: sulfate ion not precipitate

halide test method

1. if solid, first make solution of halide salt in dilute nitric acid.

2. add 1cm3 of silver nitrate solution, observe

3. add 1cm3 of dilute ammonia solution 

4. if precipitate remains, add excess 5cm3 of dilute ammonia solution 

5. if precipitate remains, repeat the process using concentrated ammonia solution

result chloride

white precipitiate - dissolves in both dilute ammonia solution and concentrated ammonia solution to form colourless solution

bromide result

cream precipitate - not dissolves in dilute ammonia solution but does in concentrated ammonia solutionto form colourless solution 

iodide results

yellow precipitate does not dissolve in either dilute or concentrated ammonia solution

carbonate ion test method and results

add some dilute acid , if there is effervescene, bubble any gas produced into limewater

if carbonate is present , a gas is produced that changes limewater from coloulress to milky

ammonium ion test method

1. add dilute sodium hydroxide to solid sample

2. heat gently (dont want ammonia gas)

3. any gas produces is test with damp universal indicator paper, or with glass rod dipped in concentrated hydrochloric acid

ammonium ion test result 

pungent gas produced (ammonia)

gas changes damp universal indicator paper blue

white smoke produced with concentrated hydrochloric acid