8. Chemical Analysis

What is a pure substance in chemistry?

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

How can melting point and boiling point data be used in chemical analysis?

They can distinguish pure substances from mixtures because pure substances have specific melting and boiling points.

What does "pure" mean in everyday language?

A substance that is unadulterated and in its natural state, like pure milk.

What is a formulation?

A mixture designed as a useful product where each chemical has a particular purpose.

Give examples of formulations.

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

What is chromatography used for?

Separating mixtures and helping identify substances.

What are the two phases in chromatography?

The stationary phase and the mobile phase.

How is separation achieved in chromatography?

By the distribution of substances between the stationary and mobile phases.

How do you calculate the Rf value in chromatography?

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

Why are Rf values useful?

Different compounds have different Rf values in different solvents, which helps identify compounds.

What indicates a pure compound in chromatography?

A single spot in all solvents.

How can chromatography distinguish pure substances from impure substances?

Pure substances produce one spot; mixtures produce multiple spots.

What is the test for hydrogen gas?

Holding a burning splint at the open end of a test tube; hydrogen burns with a pop sound.

What is the test for oxygen gas?

Inserting a glowing splint into the gas; the splint relights in oxygen.

What is the test for carbon dioxide gas?

Bubbling carbon dioxide through limewater, which turns milky.

What is the test for chlorine gas?

Damp litmus paper is bleached and turns white when exposed to chlorine gas.

Why are instrumental methods important in chemical analysis?

They provide fast, sensitive, and accurate analysis, especially for small amounts of chemical.