GCSE Chemistry: chemical analysis

Flashcards covering vocabulary and key concepts from the GCSE Chemistry lecture on Atomic Structure and the Periodic Table.

Pure substance

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

Testing for purity

Comparing the melting and boiling point with the known pure substance.

Effect of impurities on melting/boiling points

Impurities lower the melting point and raise the boiling point, widening the range.

Formulation

A mixture that has been designed as a useful product.

Examples of formulations

Paint, fuels, medicines, cleaning agents, alloys.

Importance of formulations

Each component is present in a measured quantity to ensure the product has the required properties.

Chromatography

A technique used to separate and identify substances in a mixture.

Phases in chromatography

Mobile phase (solvent) and stationary phase (paper).

Rf value

Rf = distance moved by substance / distance moved by solvent.

Test for hydrogen

A lit splint makes a squeaky pop.

Test for oxygen

A glowing splint relights.

Test for carbon dioxide

Turns limewater cloudy.

Test for chlorine

Bleaches damp litmus paper white.

Flame test

Identifies metal ions based on flame colour.

Flame colour of lithium

Crimson red.

Flame colour of sodium

Yellow.

Flame colour of potassium

Lilac.

Flame colour of calcium

Orange-red.

Flame colour of copper

Green.

Precipitate formed by calcium with NaOH

White.

Precipitate formed by aluminium with NaOH

White at first, then dissolves in excess NaOH.

Precipitate formed by magnesium with NaOH

White.

Precipitate formed by copper(II) with NaOH

Blue.

Precipitate formed by iron(II) with NaOH

Green.

Precipitate formed by iron(III) with NaOH

Brown.

Test for carbonates

React with acid to form carbon dioxide, which turns limewater cloudy.

Test for sulfates

Add HCl and barium chloride; a white precipitate forms.

Test for halides

Add nitric acid and silver nitrate: chloride (white), bromide (cream), iodide (yellow).

Advantages of instrumental analysis

Accurate, sensitive, fast.

Flame emission spectroscopy

An instrumental method to identify metal ions and determine their concentration.

Function of flame emission spectroscopy

Each metal ion produces a characteristic line spectrum when heated.

Intensity of lines in a spectrum

Indicates the concentration of the metal ion.