C12 - Chemical Analysis

What is an impure and pure substance?

Pure - contain only one substance, can be a compound or element

impure - a mixture of two or more different elements or compounds

Pure elements and compounds melt and boil at …?

Specific temperatures, and these fixed points are used to identify them

What can melting and boiling point data be used for?

used to distinguish pure substances from mixtures (that melt or boil over a range of temperatures)

What are formulations?

Formulations are useful mixtures, made up in definite proportions, designed to give a product the best properties to carry out its specific function.

Name a method scientists can use to identify unknown substances in solution?

Paper chromatography

What can retention factor (R) be used for?

Can be measured and matched against databases to identify specific substances.

Rf =

distance moved by substance/distance moved by solvent

Name a method of testing for hydrogen

A lighted splint pops

Name a method of testing for Oxygen

relights a glowing splint

Name a method of testing for Carbon dioxide

turns limewater milky (cloudy)

Name a method of testing for Chlorine gas

bleaches damp blue litmus paper white

What substances could be identified through flame test?

Some metal ions (including most Group 1 and Group 2 cations) can be identified in their compounds using flame tests

What can sodium hydroxide solution identify?

metal ions that form insoluble hydroxides in precipitation reactions

How can you identify carbonates?

By adding dilute acid, which produces carbon dioxide gas. The gas turns limewater milky (cloudy)

How can you identify halides?

By adding nitric acid, then silver nitrate solution. This produces a precipitation of silver halide (chloride = white, bromide = cream, iodide = yellow.

How can you identify sulfates?

By adding hydrochloric acid, then barium chloride solution. This produces a white precipitate of barium sulfate.

What do modern instrumental techniques provide?

Fast, accurate and sensitive ways of analysing chemical substances

Name an example of an instrumental method?

Flame emission spectroscopy

What can flame emission spectroscopy identify?

This method tell us which metal ions are present from their characteristic line spectra , and also the concentration of the metal ions in a solution.

Name some examples of formulations?

fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.

What is the stationary and the mobile phase?

The 'mobile phase' refers to the molecules that can move

.A substance which is more soluble in the mobile phase will spend more time in the mobile phase. This means it will move faster, and travel a further distance up the paper

The 'stationary phase' refers to the molecules that can't move.

A substance which is less soluble in the mobile phase will spend more time in the stationary phase, so move slower, and not travel very far up the paper.

What colour is each metal ion under a flame?

Lithium - red

sodium - yellow

potassium - lilac/purple

Calcium - orange-red

copper - blue-green