Lesson 1: Chromatography Flashcards
What is a “chromatogram?”
A chromatogram is the dried result of soluble dyes travelling up the paper.
Why do you put a lid on the beaker?
- To reduce solvent evaporation
What is the solvent front?
- Marked point where the solvent rises to.
What are the 2 main types of solvents you use in chromotography?
- Water
- Ethanol
What is the Rf value?
- The Rf value is the ratio of distance moved by the compound to the distance moved by solvent.
How do you calculate the Rf value ?
Rf = distance moved by chemical/ distance moved by solvent
How can you use Rf value to identify a chemical?
- Look in a data book.
Why is it difficult to always find a chemical from its Rf value?
- Many chemicals have the same Rf value.
- If the chemical isn’t identified yet, it won’t be in the data book.
What would you have to do if the Rf value of an unknown chemical is the same as others?
- Use a different solvent to narrow it down.
What is the “mobile phase”?
- Moving part —> solvent
What is the “stationary phase”?
- Stationary part —> paper
Why don’t you just measure the length from baseline to centre of compound when identifying a chemical?
- The length depends on how long it’s been kept.
- So you do a ratio
What will happen when a pure substance is used?
- There will be a single dot.
What 2 factors affect the Rf value?
- Solvent (mobile phase)
- Paper (stationary phase)
Why are there sometimes different Rf values fo pure substances?
- If you change the solvent/ paper, this will affect the Rf value.
