Topic 8 - Chemical Analysis Flashcards
What’s a pure substance?
Something that only contains one compound or element throughout
Is milk a pure substance?
No it contains calcium
A chemically pure substance will melt or boil at a _________ temperature
Specific
How can you test the purity of a sample?
Measure its boiling or melting point and compare it with the melting or boiling point of the pure substance - the closer the value, the purer the sample
Impurities in a sample will _______ the boiling point and may result in the sample boiling at a _______ of temperatures
Increase
Range
What are formulations?
Useful mixtures with a precise purpose that are made by following a formula (precise measurements)
Give examples of how formulations are used in everyday life
Formulation of a pill, cleaning products, fuels, cosmetics, food, drink
What’s an impure substance?
A mixture of elements and compound
What’s the mobile phase in chromatography?
The solvent that moves up the paper
What’s the stationary phase in chromatography?
The paper
How many spots will a pure substance form?
1
Do more or less soluble compounds move higher up the chromatography paper?
More soluble
What does it mean if a substance hasn’t moved off the start line?
It’s insoluble
What’s the top line on a chromatogram called?
Solvent front
How to calculate Rf value?
Distance travelled by substance / Distance travelled by solvent
So… dot / solvent
Explain how different dyes are separated by paper chromatography
- Substances have different solubilities in the mobile and stationary phase
- Substances that are more soluble in the mobile phase, move faster in the solvent and are carried further up the paper
- Substances more attracted to the stationary phase, move slower and stay closer to the start line
