4.8 Chemical Analysis

AQA Chemistry

What is the test for oxygen?

Insert a glowing splint into the test tube → should relight

What is the test for hydrogen?

Insert a lit split near mouth of tube → should make a squeaky pop

What is the test for carbon dioxide?

Bubble gas through limewater (calcium hydroxide) → turns limewater cloudy

What is the test for chlorine?

Insert damp litmus paper into the test tube → should turn from red to white (bleached)

What is a pure substance?

A single element or compound not mixed with any other substance.

What are characteristics of a pure substance?

Has a specific melting and boiling point

What is a formulation?

A mixture with a specific purpose - with ingredients in specific proportions.

What are examples of a formulation?

• Tablets

• Paint

• Medicines

• Alloys

• Fertilisers

• Foods

What colour is the flame for Lithium?

Crimson

What colour is the flame for Sodium?

Yellow

What colour is the flame for Potassium?

Lilac

What colour is the flame for Calcium?

Orange-red

What colour is the flame for Copper?

Green

What colour is the precipitate for Calcium?

White

What colour is the precipitate for Copper?

Blue

What colour is the precipitate for Iron (II)?

Green

What colour is the precipitate for Iron (III)?

Brown

What colour is the precipitate for Aluminium?

White

What colour is the precipitate for Magnesium?

White

What is produced when a carbonate is reacted with dilute acid?

Carbon Dioxide, a Salt and Water

How do you test for halide ions?

Add dilute nitric acid (HNO₃), followed by silver nitrate solution (AgNO₃)

What colour is the precipitate for Chloride ?

White

What colour is the precipitate for Bromide?

Cream

What colour is the precipitate for Iodide?

Yellow

How do you test for sulfate ions?

Add dilute hydrochloric acid (HCl), followed by barium chloride solution (BaCl₂)

What happens if sulfates are present?

A White precitipate forms

Why is hydrochloric acid used?

To react with and remove carbonates which would otherwise produce a white precipitate and create invalid results

What are advantages of flame emission spectroscopy?

• It is accurate

• It is sensitive

• It is rapid

How do you work out Rf Value?

distance moved by substance / distance moved by solvent