AQA · Chemistry · 8462
GCSE Chemistry (AQA): Paper Chromatography
Topic 8 — Chemical Analysis. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - Paper Chromatography"; each card deep-links to the moment in the video it came from. Lesson 8.02 of Cognito's AQA GCSE Combined Science (Trilogy) and Chemistry course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-c_8.02.
14 flashcards · Free to study · No account needed
Study this deck
Preparing your cards…
All questions and answers
Read through the full deck, or practise recalling each answer above.
How many spots does a pure substance produce on a chromatogram?
Show answer
One — a pure substance contains only one chemical, so it cannot separate out.
What is the mobile phase in chromatography?
Show answer
The substance the molecules can move in — always a liquid or a gas. In paper chromatography it is the solvent.
Why must the solvent level be below the baseline in paper chromatography?
Show answer
So the ink spots are not submerged and dissolved straight into the solvent instead of travelling up the paper.
What is the equation for the Rf value?
Show answer
Rf = distance travelled by the substance ÷ distance travelled by the solvent.
Why do more soluble substances travel further up chromatography paper?
Show answer
They spend more time in the mobile phase (dissolved in the solvent) and less time bound to the paper, so they move faster.
The pattern of separated spots left on the dried paper after chromatography is called a ?.
Show answer
chromatogram
Which two experimental conditions must be stated alongside an Rf value?
Show answer
The solvent used and the type of paper used — changing the mobile or stationary phase changes the Rf value.
What is the stationary phase in paper chromatography?
Show answer
The paper — a substance the molecules cannot move in (usually a solid or a very thick liquid).
Why must the baseline in paper chromatography be drawn in pencil?
Show answer
Pencil is insoluble, so it will not dissolve in the solvent and travel up the paper.
A spot moves 6 cm while the solvent moves 10 cm — what is its Rf value?
Show answer
0.6 (6 ÷ 10). Rf values have no units.
What is chromatography used for?
Show answer
Separating the different substances in a mixture so they can be identified.
Why is the Rf value used instead of the distance a substance travelled?
Show answer
The actual distance depends on how long the experiment is left running, whereas the ratio is constant for a given substance, solvent and paper.
Why is a lid placed on the beaker during paper chromatography?
Show answer
To stop the solvent evaporating.
In paper chromatography, what happens to a substance that is insoluble in the solvent?
Show answer
It stays on the baseline, because it cannot dissolve and move up the paper.
Want to create your own cards? Create a free account. AI generation uses credits.