Chromatography Rf Worksheet Generator

A chromatogram is read by distances: how far the solvent travelled from the start line, how far each spot travelled, and which spots of a mixture sit level with spots of known standards. This draws synthetic chromatograms — lettered standards, a mixture X with numbered spots, a start line and a solvent front — beside their own millimetre scale, and asks for the solvent distance, an Rf value, and what X could contain. Standard sheets include a spot that matches no standard; stretch sheets have two standards too close for the solvent to separate, and a spot that never left the start line.

Level

How many chromatograms

1 to 4, one to a printed page.

Sheet code (optional)

Leave empty for a fresh sheet. The same code and settings make the same sheet again while the generator is unchanged. The code is a seed: deterministic, not cryptographic, and not a secret.

The chromatograms are synthetic: the standards are lettered, not real substances. Read positions to the nearest millimetre from the scale drawn beside each one; spots 2 mm apart or closer cannot be told apart. Every spot is drawn in the same grey, so the sheet does not depend on colour.

Paper size

Print size

Margin

Millimetres of blank edge, 5 to 40.

Turn the paper sideways

How to print this, or save it as a PDF

There is no PDF to download, and there does not need to be. Open the print command in your browser and choose “Save as PDF” as the destination. Your browser decides whether the page address and date print across the top and bottom; if they appear, turn off “Headers and footers” in the print dialog.
Set the scale to 100%, not “fit to page”. This sheet is already the exact size of the paper you chose, so anything that resizes it makes every measurement on it wrong.
Leave the paper size in the dialog set to the same one you chose here.

The sheet will appear here.

What this generator does

Places the standards' spots at whole millimetres well apart, builds mixture X from some of those positions (and, by level, a spot matching none, a spot on the start line and a pair of standards only 2 mm apart), and draws it all to scale. Every answer is then worked out again from the drawn positions alone, using the reading rule printed on the sheet.

How to use this tool

Choose a level and how many chromatograms.
Press Make the sheet, then Show the answers to check.
Print the questions and the answers, one chromatogram to a page, or type a sheet code to make the same sheet again.

Understanding the controls

Level: Gentle has three standards and every spot of X matches one; standard has four standards and a spot of X that matches none; stretch adds two standards too close to separate and a spot that stays on the start line.
How many chromatograms: 1 to 4. Each prints on its own page with its questions, and the answers follow.
Sheet code: Leave empty for a fresh sheet from the browser's secure generator; with a code, the same code and settings make the same sheet again while the generator is unchanged.

Worked examples

Code harbour, standard, chromatogram 1: The solvent travelled 80 mm. X's spots are at 38, 48 and 64 mm: spot 2 has Rf 48 ÷ 80 = 0.60; X could contain D (38) and C (64), and the spot at 48 mm matches no standard.
Code harbour, stretch, chromatogram 1: Standards A and B are at 26 and 24 mm, so X's spot at 24 mm could be either: this solvent cannot separate them. Spot 1 never left the start line.

Common use cases

Rf calculation practice with a different chromatogram each time
Interpreting matches, non-matches and poor separation
Homework on what a chromatogram can and cannot show

How this generator works

Rf is the distance from the start line to the centre of the spot divided by the distance from the start line to the solvent front. Positions are read to the nearest millimetre, and the sheet's rule is that spots 2 mm apart or closer cannot be told apart; spots of X are never drawn between 3 and 6 mm from a standard, so every reading is either clearly level or clearly not. A spot of X level with a standard could be that substance; level with two standards, either; level with none, something else.

Randomness and fairness

Positions come from the browser's secure generator, or a seeded one when you type a code. A code repeats a sheet while the generator is unchanged. Codes are deterministic, not cryptographic, and not a secret.

For how randomness is produced across the whole site, see how Generate Random works.

Assumptions this tool makes

All lanes ran on the same paper with the same solvent, so their Rf values can be compared.
The standards are lettered placeholders, not real substances, and the chromatograms are synthetic.

Limitations and good to know

Spots are neat ellipses; real spots streak, spread and overlap.
One solvent per chromatogram; two-way chromatography and locating agents are not covered.
A worksheet for interpreting chromatograms, not instructions for running one.

Common mistakes

Measuring from the bottom of the paper: Both distances are measured from the start line, where the spots were put on.
Measuring to the top of a spot: Measure to the centre of the spot.
Taking a match as proof: Different substances can travel the same distance in one solvent; a match is evidence, and a second solvent is a better test.

Privacy and your data

Sheets are built in your browser. With analytics consent, a count records how many chromatograms a sheet had; the sheet and any code are not sent.