1. Learning Objective Carry out and describe chromatography
To be able to:
Carry out and describe chromatography
Key Words:
Chromatography, mixture, ratio

2. Chromatography Exam question Sunday, 26 May 2019
Date and title in books. You need a pen, pencil & ruler.
Starter Activity – 5 minutes
Exam question

3. (F)
Target 9-1
Identify how chromatography is carried out in a science lab
(F/H)
Target 4-9
Describe how chromatography works
(H)
Target 5-9
Calculate Rf values using given information
Extension: Application of Knowledge
Target 8/9
Compare gas chromatography and liquid chromatography
Learning Outcomes

4. What is chromatography?
The process of separating a mixture by passing it through a medium in which the components pass at different speeds.
Important Definition

6. Task
We are going to carry out chromatography on a sample of pen ink. We will use our chromatograms later in the lesson.

7. Rf Values
We want to calculate how far compound (colour of ink in our case) has travelled, compared to how far the solvent (water in our case) has travelled. We call this the Rf value.
Rf = distance moved by a substance
distance moved by solvent

8. Rf = Distance travelled by component/Distance travelled by solvent
Calculating Rf Values
6cm
This sample contained green ink and orange ink
This sample contained green ink
2cm
Rf = 2/6 = 0.3 (1sf)
Rf = Distance travelled by component/Distance travelled by solvent

9. Using Rf Values
Different compounds have different Rf values. We can look up the Rf value of an unknown compound in order to identify it. By looking up the Rf values of the green and orange inks in the example we could find out exactly which inks they were.

10. Gas vs liquid chromatography
Gas chromatography is used in chemical industries.
Why might they use a gas instead of a liquid?
They are detected by a computer, so it makes the results more accurate
They are much faster
They are more sensitive (only a small amount of substance is needed)