Purity, formulations and chromatography (8.1) Flashcards
In Chemistry, what is a pure substance?
a single element or compound, not mixed with any other substance
Pure elements and compounds melt and boil at (…) temperatures
specific
What can be used to distinguish pure substances from mixtures?
Melting point and boiling point data
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
How can boiling and melting point data be used to distinguish pure from impure substances?
Pure substances have a sharp melting point but mixtures (impure substances) melt over a range of temperatures (depending on proportions/ratio of substances within mixture)
What is a formulation?
a mixture that has been designed as a useful product
may have to give additional info found on next two cards
How are the useful products (not chemically created products) created from formulations designed for purpose?
Many products are 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
7 needed
What are examples of formulations?
- fuels
- cleaning agents
- paints
- medicines
- alloys
- fertilisers
- foods
What are the two uses of chromatography?
separate mixtures (of soluble compounds) and can give information to help identify substances
What are the two phases of chromatography?
stationary phase and mobile phase
What is the stationary phase of chromatography?
Phase in chromatography that does not move, for instance, the paper in paper chromatography.
What is the mobile phase of chromatography?
the solvent that moves through the paper, carrying different substances with it
Separation in chromatography depends on what?
the distribution of substances between the phases
What is the Rf value?
The ratio of the distance moved by a compound (centre of spot from origin) to the distance moved by the solvent
How is the Rf value calculated?
cannot be above 1
What can be used to help identify the compounds in chromatography?
The fact that different compounds have different Rf values in different solvents
Describe the difference in observations on a chromatogram for mixtures and pure substances
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
How far the substance travels up the solvent on a chromatogram depends on what?
The distribution between the phases.
If the substances are more attracted to the mobile phase, they will travel up the chromatogram faster and spend more time in the mobile phase, if they are more attracted to the stationary phase, they will travel up slower and spend mroe time in the stationary phase
Why should a pencil line, not a pen line, be drawn in paper chromatography?
The ink (of the pen) will mix with the sample and run into the chromatogram, so results cannot be properly observed
Why should the mobile phase (solvent) be placed underneath the pencil line in paper chromatography?
The substances (solutes e.g. ink) will diffuse into the water and wash away, so no results are produced on the chromatogram
