Analytical Chemistry and Kinetics

Tests for Ions and Gases

Flame Tests: Taking a piece of nichrome, make loop at the end and dip into salts containing ions

Ion	Colour
Li⁺	Crimson red
Na⁺	Yellow orange
K⁺	Lilac
Ca²⁺	Brick red/orange red

Using Sodium Hydroxide solution

Ion	Colour of Precipitate
Cu²⁺	Blue
Fe²⁺	Sludgy Green (or just green)
Fe³⁺	Orange Brown (rust)

For Ammonium Ions (NH₄⁺)

Heat gently and add sodium hydroxide solution. It will give off a distinctive smell of ammonia (NH₃). Ammonia can be tested by holding a damp red litmus paper. Since it is alkaline, it will turn damp red litmus paper from red to blue.

Using Dilute Nitric Acid and Silver Nitrate Solution

Ion	Colour of Precipitate
Cl^–	White
Br^–	Pale Cream
I^–	Yellow

For Sulphate Ions (SO₄^2-)

Using dilute hydrochloric acid solution and then adding barium chloride solution to form a white precipitate of barium sulphate.

For Carbonate Ions (CO₃^2-)

Using dilute hydrochloric acid to react with the carbonate, to produce carbon dioxide gas which can be tested by bubbling through limewater, turning it from colourless to cloudy, milky white.

Tests for Gases

Gas	Test	Result
Hydrogen	Hold a lit splint in presence of hydrogen gas.	Produces a squeaky pop.
Oxygen	Hold a glowing splint in presence of oxygen gas.	Glowing splint relights.
Carbon Dioxide	Bubble through limewater.	Turns limewater from colourless to cloudy, milky white.
Ammonia	Hold damp red litmus paper in ammonia gas.	Turns damp red litmus paper blue.
Chlorine	Hold damp blue litmus paper in chlorine gas.	Bleaches or turns blue litmus paper white.

Solubility Patterns

All nitrates are soluble.
All sodium, potassium and ammonium compounds are soluble.
Most carbonates and hydroxides are insoluble except for sodium, potassium and ammonium.
All sulphates are soluble except barium and lead(II) sulphate.
All chlorides are soluble except lead(II) and silver chloride.

Reactions of Metals to Acids

Metals react very similarly to dilute hydrochloric acid and dilute sulphuric acid.

Metals	Reaction to Acid
Magnesium	Rapid fizzing, mixture gets very hot, colourless magnesium sulphate/chloride solution forms.
Aluminium	Is slow due to its coat of aluminium oxide which prevents aluminium from contacting the acid. On heating, this layer is removed, aluminium will start fizzing rapidly – abit like Mg.
Zinc	Zinc reacts slowly with cold dilute acid and may produce some effervescence. On heating however, it fizzes more.
Iron	Iron also reacts slowly with cold dilute acid and will produce abit of effervescence when heated.

Combustion of Hydrogen

Bonds are broken in the hydrogen and oxygen molecules. These form new bonds of water molecules. This reaction is exothermic, and gives out water in the form of steam, before it condenses into a liquid. The reaction is:

2H₂(g) + O₂(g) -> 2H₂O(l)

Testing for Water

Water turns white anhydrous copper(II) sulphate blue. It’s reaction is

CuSO₄(s) + 5H₂O(l) -> CuSO₄•5H₂O

Or you can use cobalt chloride paper – which turns pink in the presence of water.

You can check the purity of water by showing that it freezes at exactly 0ºC and boils at exactly 100ºC.