TOPIC 8 - CHEMICAL ANALYSIS Flashcards
What is a pure substance?
Something that only contains one compound or element throughout.
What tells you how pure a substance is?
The melting and boiling point tells you how pure a substance is. A chemically pure substance will melt or boil at a specific temperature (the values can be found in a data book). The closer the point you measured is to the actual point, the more pure the sample is.
What are formulations?
Formulations are mixtures with exact amounts of components. 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.
Paint is a formulation composed of what?
Pigment
Solvent
Binder (resin)
Additives.
What are formulations important?
Pharmaceutical industry. E.g. by altering the formulation of a pill, chemists can make sure it delivers the drug to the correct part of the body at the right concentration, that it is consumable, and has a long enough shelf life.
What is chromatography?
Analytical method used to separate the substance in a mixture. You can use it to identify the substances.
What is the mobile phase of chromatography?
Where the molecules can move. This is always a liquid or a gas.
Solvent.
What is the stationary phase of chromatography?
Where the molecules can’t move. This can be solid or a really thick liquid.
The chromatography paper.
What happens during a chromatography experiment?
The substances are constantly moving between the mobile and stationary phase - an equilibrium is formed between the two phases.
The mobile phase moves through the stationary phase, and anything dissolved in the mobile phase moves with it.
What decides how quickly a chemical moves during chromatography?
How quickly a chemical moves depends on how it is distributed between the two phases - whether it spends more time in the mobile phase or the stationary phase.
The chemicals that spend more time in the mobile phase than the stationary phase will move further through the stationary phase.
When will components in a mixture normally separate during chromatography?
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.
What factors affect how long the molecules spend in each phase?
How soluble they are in the solvent.
How attracted they are to the paper.
Molecules with higher solubility in the solvent, and which are less attracted to the paper, will spend more time in the mobile phase - and they will be carried further up the paper.
What is a chromatogram?
The result of chromatography.
What is Rf value?
The ratio between the distance travelled by the dissolved substance (the solute) and the distance travelled by the solvent. The further through the stationary phase a substance moves, the larger the Rf value.
What is the formula for the Rf value?
Rf = distance travelled by substance (B) / distance travelled by the solvent (A).
What can the Rf value be used for?
Chromatography is often carried out to see if a certain substance is present in a mixture. To do this, you run a pure sample of that substance (a reference) alongside the unknown mixture. If the Rf values match, the substance may be present.
However, the Rf value is also dependent on the solvent - if you change the solvent the Rf value for a substance will change. So, you test both the mixture an the reference in a number of different solvents.
What is the test for chlorine gas?
Chlorine bleaches damp litmus paper, turning it white. (it may turn red for a moment first because a solution of chlorine is acidic).
