Chemical Analysis - P2T8

Chromatogram

A graph that shows the result of separating the components of a mixture by chromatography.

Chromatography

A technique used to separate mixtures due to the distribution of the substances between the stationary and mobile phase. It can give information to help identify substances.

Flame emission spectroscopy

An instrumental method used to analyse metal ions in solutions.

Flame test

Qualitative test used to identify metal ions (cations). Carried out by inserting a nichrome wire loop with the unknown compound on into a flame and observing the colour.

Formulation

A mixture that has been designed as a useful product. They are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.

Impure substance

A substance made up of two or more elements or compounds that are not bonded together chemically.

Instrumental methods

What methods can be used to detect and identify elements and compounds?

Litmus paper

Paper stained with litmus which can be used to indicate the acidity or alkalinity of a substance. Used in the test for chlorine.

Mobile phase

When the molecules can move during chromatography. It is always a liquid or gas.

Precipitation

The creation of a solid from a solution.

Pure substance

A single element or compound, not mixed with any other substance. In everyday language, a ____ can mean a substance that has had nothing added to it, so it is unadulterated and in its natural state.

Rf value

The ratio of the distance moved by a compound to the distance moved by the solvent.

Stationary phase

Where the molecules are still during chromatography. It is a solid or a liquid supported on a solid.

Copper test

When heated, ____ salts produce a characteristic blue flame. ____ ions form a blue solution.

Chlorine test

Add ____ water to a solution of sodium chloride (NaCl). The____ turns the solution yellow-green.

Hydrogen test

When what gas is added to a flame, it burns with a 'pop' sound.

Advantages of using instrumental methods instead of chemical tests

• (more) accurate

• (more) sensitive

• fast(er)

• determine the concentration of ions present

• requires a small(er) sample

How to work out Rf value?

Distance travelled by substance / Distance travelled by solvent

(smaller/ bigger)

Flame test Lithium Li⁺

Crimson flame

Flame test Sodium Na⁺

Yellow flame

Flame test Potassium K⁺

Lilac flame

Flame test Calcium Ca²⁺

Orange-red flame

Flame test Copper(II) Cu²⁺

Green flame

Sodium hydroxide test Calcium Ca²⁺

White precipitate, does not dissolve in excess NaOH

Sodium hydroxide test Magnesium Mg²⁺

White precipitate, does not dissolve in excess NaOH

Sodium hydroxide test Aluminium Al³⁺

White precipitate, dissolves in excess NaOH

Sodium hydroxide test Copper(II) Cu²⁺

Blue precipitate

Sodium hydroxide test Iron(II) Fe²⁺

Green precipitate

Sodium hydroxide test Iron(III) Fe³⁺

Brown precipitate

Carbonate test Any carbonate CO₃²⁻

Add dilute acid → bubbles of gas → turns limewater cloudy

Sulfate test Any sulfate SO₄²⁻

Add dilute HCl then barium chloride → white precipitate

Halide test (chloride) Sodium chloride Cl⁻

Add dilute nitric acid then silver nitrate → white precipitate

Halide test (bromide) Sodium bromide Br⁻

Add dilute nitric acid then silver nitrate → cream precipitate

Halide test (iodide) Potassium iodide I⁻

Add dilute nitric acid then silver nitrate → yellow precipitate