Chemical Analysis Flashcards
Pure in everyday life
a pure substance consist only of that substance
Pure in chemistry
a pure substance consists only of one element or one compound
Pure Substance B and M Point
Pure substances have a sharp melting point and boiling point
Impure Substance B and M point
Decreases melting point and increases boiling point and increases the range.
Formulation
A formulation is a mixture which has been designed as a useful product.
Chromotography
Paper chromatography is used to separate mixtures of soluble substances and to provide information on the possible identity of the substances present in the mixture.
Mobile Phase
the mobile phase is the solvent that moves through the paper, carrying different substances with it
Stationary Phase
the stationary phase is contained on the paper and does not move through it
Why do they move at different rates
The different dissolved substances in a mixture are attracted to the two phases in different proportions. This causes them to move at different rates through the paper.
What’s the difference between a pure and impure substances on a chromatogram
A pure substance produces one spot on the chromatogram.
An impure substance produces two or more spots
Two substances are likely to be the same if
they produce the same number of spots, and these match in colour
the spots travel the same distance up the paper (have the same Rf value)
Rf value use
Rf values can be used to identify unknown chemicals if they can be compared to a range of reference substances.
The Rf value is always the same for a particular substance if run in the same solvent system.
Rf equation
Rf = distance travelled by substance/ distance travelled by solvent
Precipitate
a substance to be deposited in solid form from a solution
Why are instrumental methods better ?
- more accurate
- more rapid
- more sensitive
