Chemical Analysis Flashcards
What is the definition of purity in chemistry?
A pure substance contains only one compound or element throughout, not mixed with anything else.
This differs from everyday definitions of purity.
How can the purity of a substance be tested?
By measuring its melting or boiling point and comparing it with the known melting or boiling point of the pure substance.
This information can be found in a data book.
What effect do impurities have on the melting point of a substance?
Impurities lower the melting point and increase the melting range of the substance.
This indicates that the sample is not pure.
What effect do impurities have on the boiling point of a substance?
Impurities increase the boiling point and may cause the sample to boil at a range of temperatures.
What are formulations?
Formulations are mixtures with exact amounts of components, made by following a ‘formula’.
They serve a precise purpose.
List the components typically found in paint formulations.
- Pigment
- Solvent
- Binder (resin)
- Additives
Why are formulations important in the pharmaceutical industry?
They ensure drugs are delivered to the correct part of the body at the right concentration and have a suitable shelf life.
In what everyday products can formulations be found?
- Cleaning products
- Fuels
- Cosmetics
- Fertilisers
- Metal alloys
- Food and drink
True or False: The composition of a formulation is often indicated on its packaging.
True
Fill in the blank: A chemically pure substance will melt or boil at a _______ temperature.
[specific]
What was the measured melting point range of the student’s aspirin sample?
128-132 °C
What are the melting and boiling points of pure aspirin?
- Melting point: 136 °C
- Boiling point: 140 °C
Give two reasons why the melting point measured shows that the sample is not pure.
- The melting point is lower than the pure substance’s melting point.
- The melting range is wider than that of a pure substance.
Suggest a value for the boiling point of the sample based on its purity.
[value based on the context of impurities]
What is chromatography?
An analytical method used to separate the substances in a mixture.
What are the two phases in chromatography?
- Mobile phase
- Stationary phase
What is the mobile phase in chromatography?
A liquid or a gas where the molecules can move.
What is the stationary phase in chromatography?
A solid or a really thick liquid where the molecules can’t move.
What forms during a chromatography experiment?
An equilibrium between the mobile and stationary phases.
What determines how quickly a chemical moves in chromatography?
How it is distributed between the mobile and stationary phases.
What happens to chemicals that spend more time in the mobile phase?
They will move further up the stationary phase.
What is the stationary phase in paper chromatography?
Chromatography paper, often filter paper.
What is the mobile phase in paper chromatography?
The solvent (e.g., ethanol or water).
What factors influence the time molecules spend in each phase?
- Solubility in the solvent
- Attraction to the paper
