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

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

(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

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

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

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

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

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.

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)