Purity, formulations and chromatography + Identification of common gases

In chemistry, what is a pure substance?

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

What do pure elements and compounds melt and boil at?

Specific temperatures. Melting point and boiling point data can be used to distinguish pure substances from mixtures.

In everyday language, what can a pure substance mean?

A substance that has had nothing added to it, so it is unadulterated and in its natural state, eg pure milk.

What is a formulation?

A mixture that has been designed as a useful product.

What are many products?

Complex mixtures in which each chemical has a particular purpose.

How are formulations made?

By mixing the components in carefully measured quantities to ensure that the product has the required properties. Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods

What can chromatography can be used to separate?

Mixtures and can give information to help identify substances.

What can chromatography involve?

A stationary phase and a mobile phase.

What does seperation depend on?

The distribution of substances between the phases.

What is an Rf value?

The ratio of the distance moved by a compound (centre of spot from origin) to the distance moved by the solvent.

What is the equation for Rf value?

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

What do different compounds have?

Different Rf values in different solvents, which can be used to help identify the compounds.

What might the compounds in a mixture may separate into?

Different spots depending on the solvent but a pure compound will produce a single spot in all solvents.

What is the test for hydrogen?

The test for hydrogen uses a burning splint held at the open end of a test tube of the gas. Hydrogen burns rapidly with a pop sound.

What is the test for oxygen?

The test for oxygen uses a glowing splint inserted into a test tube of the gas. The splint relights in oxygen.

What is the test for carbon dioxide?

The test for carbon dioxide uses an aqueous solution of calcium hydroxide (lime water). When carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy).

What is the test for chlorine?

The test for chlorine uses litmus paper. When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white.