Chemistry Paper 2 Topic 8 – Chemical Analysis
Purity and Formulations
In chemistry, a pure substance is something that only contains one compound or element
throughout – not mixed with anything else.
The Boiling or Melting Point shows how Pure a Substance is:
A chemically pure substance will melt or boil at a specific temperature.
You can test the purity of a sample by measuring its melting and boiling point and
comparing it with the melting or boiling point of the pure substance.
The closer your measured value is to the actual melting or boiling point, the
purer your sample is.
Impurities in your sample will lower the melting point and increase the melting
range of your substances.
Impurities in your sample will also increase the boiling point and may result in your
sample boiling at a range of temperatures.
Formulations are mixtures with exact amounts of components, with a precise purpose.
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.
They are vital in the
pharmaceutical industry; 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’s its
consumable and has a long enough shelf life.
In everyday life, formulations can be found in cleaning products, fuels, cosmetics, fertilisers,
metal alloys and even food and drink.
Information about a products composition (e.g. ratios or percentages of each component),
informs you of the product’s formulation and helps you choose a products with the right
composition for your particular use.
Paper Chromatography
Chromatography is an analytical method used to separate the substances in a mixture. You
can then use it to identify the substances. Despite there being different types of
chromatography, they all have the same two ‘phases’.
During a chromatography experiment, the substances in a sample constantly move between
the mobile and stationary phases – 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. 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 stationary
phase.
, Chemistry Paper 2 Topic 8 – Chemical Analysis
The chemicals that spend more time in the mobile phase than the stationary phase will
move further through the stationary phase.
The components in a mixture will normally separate through the stationary phase, so as 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.
Rf Value:
The result of chromatography analysis is called a chromatogram.
An Rf value is the ratio between the distance travelled by the dissolved substance
(the solute) and the distance travelled by the solvent. The further though the
stationary phase a substance moves, the larger the R f value.
Purity and Formulations
In chemistry, a pure substance is something that only contains one compound or element
throughout – not mixed with anything else.
The Boiling or Melting Point shows how Pure a Substance is:
A chemically pure substance will melt or boil at a specific temperature.
You can test the purity of a sample by measuring its melting and boiling point and
comparing it with the melting or boiling point of the pure substance.
The closer your measured value is to the actual melting or boiling point, the
purer your sample is.
Impurities in your sample will lower the melting point and increase the melting
range of your substances.
Impurities in your sample will also increase the boiling point and may result in your
sample boiling at a range of temperatures.
Formulations are mixtures with exact amounts of components, with a precise purpose.
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.
They are vital in the
pharmaceutical industry; 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’s its
consumable and has a long enough shelf life.
In everyday life, formulations can be found in cleaning products, fuels, cosmetics, fertilisers,
metal alloys and even food and drink.
Information about a products composition (e.g. ratios or percentages of each component),
informs you of the product’s formulation and helps you choose a products with the right
composition for your particular use.
Paper Chromatography
Chromatography is an analytical method used to separate the substances in a mixture. You
can then use it to identify the substances. Despite there being different types of
chromatography, they all have the same two ‘phases’.
During a chromatography experiment, the substances in a sample constantly move between
the mobile and stationary phases – 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. 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 stationary
phase.
, Chemistry Paper 2 Topic 8 – Chemical Analysis
The chemicals that spend more time in the mobile phase than the stationary phase will
move further through the stationary phase.
The components in a mixture will normally separate through the stationary phase, so as 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.
Rf Value:
The result of chromatography analysis is called a chromatogram.
An Rf value is the ratio between the distance travelled by the dissolved substance
(the solute) and the distance travelled by the solvent. The further though the
stationary phase a substance moves, the larger the R f value.
