IGCSE Chemistry - Separating Mixtures & Analysis

Pearson Edexcel International Specification

What is a pure substance?

A substance where all the fundamental particle units are the same. They are homogeneous

Rf values go to how many decimal places?

2

What is a mixture?

Two or more substances not chemically bonded

How would you extract a solvent from a solution?

Simple distillation

How would you separate a mixture of miscible liquids with different boiling points?

Fractional distillation

How do you filter insoluble liquids from a liquid?

Filtration

How do you separate a solute from a solution?

Evaporation / Crystallisation

How do you separate a mixture of soluble solids?

Chromatography

How do you calculate an Rf value?

spot distance / solvent distance

Test for H2

A lit splint gives a squeaky pop sound

Test for O2

A glowing splint relights

Test for CO2

Bubble gas through limewater (calcium hydroxide solution); the limewater will turn cloudy

Test for Cl2

Damp red litmus paper is bleached (turns white)

Test for NH3

Damp red litmus paper turns blu

Chemical test for water

Anhydrous copper(II) sulphate changes from white to blue

Purity test for water

Heat until boils, should boil at exactly 100 degrees C

Flame test method

Dip a length of nichrome wire into concentrated hydrochloric acid and put it into a blue Bunsen flame. This cleans the wire.

Dip the wire into the acid again, then into the sample of a solid under test. Put this into the Bunsen flame and observe the colour flame.

Flame test: Li+

red

Flame test: Na+

yellow

Flame test: K+

lilac

Flame test: Ca²+

orange - red

Flame test: Cu²+

blue - green

Precipitate test for: CO3²-

Add dilute hydrochloric acid and look for fizzing. Test the gas given off (CO2) with limewater, which goes cloudy

Precipitate test for: So4²-

Add dilute hydrochloric acid then barium chloride solution (green). A white precipitate of barium sulphate will form

Precipitate test for: Cl-

Add dilute nitric acid followed by (grey) silver nitrate solution. A white precipitate of silver chloride is formed

Precipitate test for: Br-

Add dilute nitric acid followed by (grey) silver nitrate solution. A cream coloured precipitate of silver bromide is formed

Precipitate test for: I-

Add dilute nitric acid followed by (grey) silver nitrate solution. A yellow precipitate of silver iodide is formed

Precipitate test for: Cu²+

Add (purple) dilute sodium hydroxide solution. A blue precipitate of copper(II) hydroxide will form

Precipitate test for: Fe²+

Add (purple) dilute sodium hydroxide solution. A green precipitate of iron(II) hydroxide will form

Precipitate test for: Fe³+

Add (purple) dilute sodium hydroxide solution. A brown precipitate of iron(III) hydroxide will form

Cation test: NH4+

Add (purple) dilute sodium hydroxide solution and warm the mixture. Use damp red litmus paper to test for ammonia gas; the litmus goes blue

Cation test: H+

All acidic solutions contain this ion. Blue litmus paper goes red / universal indicator goes red, orange or yellow