Chemistry - CHEMICAL ANALYSIS (C8)

Pure Substances & Formulations -

What is a pure substance in chemistry?

A substance that contains only one element / compound.

Pure Substances & Formulations -

How can you tell if a substance is pure?

It has a specific, sharp melting + boiling point.

Pure Substances & Formulations -

What happens to melting/boiling points in an impure substance?

They change - melt over a range of temperatures / at a different point than expected.

Pure Substances & Formulations -

What is a formulation?

A mixture designed to produce a useful product w/ precise amounts of components.

Pure Substances & Formulations -

Give examples of formulations.

Paint, medicines, fuels, cleaning agents, cosmetics, alloys.

Chromatography -

What is chromatography used for?

To separate + identify substances in a mixture.

Chromatography -

What are the two phases in paper chromatography?

Mobile phase - solvent

Stationary phase - chromatography paper

Chromatography -

How does chromatography separate substances?

Based on how strongly they’re attracted to the stationary phase vs. how easily they dissolve in the solvent.

Chromatography -

What is an Rf value?

Rf = distance moved by substance / distance moved by solvent

Chromatography -

What is the maximum possible Rf value?

Less than 1 (it can’t be greater than 1).

Chromatography -

How can chromatography be used to identify substances?

By comparing Rf values to those of known substances under the same conditions.

Required Practical - Chromatography -

What solvent is typically used in the paper chromatography practical?

Water / ethanol, depending on the solubility of the inks.

Required Practical - Chromatography -

Why must the ink spots be above the solvent level?

So the ink does not dissolve directly into the solvent at the bottom.

Required Practical - Chromatography -

Why should a pencil be used to draw the baseline?

Pencil is insoluble + won’t affect the results.

Gas Tests -

What is the test for hydrogen gas?

Insert a lit splint - a squeaky pop sound confirms hydrogen.

Gas Tests -

What is the test for oxygen?

Insert a glowing splint - it relights in oxygen.

Gas Tests -

What is the test for carbon dioxide?

Bubble through limewater - turns cloudy/milky.

Gas Tests -

What is the test for chlorine gas?

Damp blue litmus paper turns red, then is bleached white.

Recap & Reasoning -

Why do different compounds separate on chromatography paper?

They have different solubilities + different attractions to the paper.

Recap & Reasoning -

What makes chromatography a useful method in chemical analysis?

It can detect multiple components in a mixture + identify unkowns using Rf values.