C8 Flashcards
what is a pure substance?
a pure substance is something that only contains one compound or element.
How can you tell how pure a substance is?
the boiling or melting point
what are formulations?
Formulations are useful mixtures with a precise purpose that are made by following a ‘formula’ (a recipe). Each component in a formulation is present in a measured quantity, and contributes to the properties of the formulation so that it meets its required function.
what are the two phases of chromatography?
• A mobile phase — where the molecules can move. This is always a liquid or a gas.
• A stationary phase — where the molecules can’t move. This can be a solid or a really thick liquid.
what happens during chromatography?
1) During a chromatography experiment, the substances in the sample constantly move between the mobile and the stationary phases — an equilibrium is formed between the two phases.
2) The mobile phase moves through the stationary phase, and anything dissolved in the mobile phase moves with it. How quickly a chemical moves depends on how it’s ‘distributed’ between the two phases — whether it spends more time in the mobile phase or the stationary phase.
3) The chemicals that spend more time in the mobile phase than the stationary phase will move further.
4) The components in a mixture will normally separate through the stationary phase, so long as all the components spend different amounts of time in the mobile phase. The number of spots may change in different solvents as the distribution of the chemical will change depending on the solvent. A pure substance will only ever form one spot in any solvent as there is only one substance in the sample.
