Pupil sheet · Paper chromatography
Measure travel, then reveal what you cannot see — questions
Name ______________________ Date ____________
Try every question before you use a nudge. Write in full sentences where you are asked to explain.
1. Explain
A spot centre travelled 24 mm from the baseline. The solvent front travelled 60 mm from that same line. Fill the gaps to calculate Rf and state whether it has a unit.
Spot distance (top of the fraction) / mm
Front distance (bottom of the fraction) / mm
Rf
Unit of Rf
Nudge (only if you are stuck): Which distance belongs on top? What happens to equal distance units when you divide?
2. Explain
A removed, dry colourless chromatogram looks blank. Choose a useful next action and explain what it could reveal.
Circle one answer.
- Apply suitable locating agent to the removed dry paper
- Add locating agent to the developing reservoir instead of solvent
- Draw coloured spots wherever expected
What has already happened before the agent is applied?
Nudge (only if you are stuck): Have the substances already separated? Which later step makes their positions visible?
3. Calculate
The baseline is 12 mm above the paper's bottom edge. The spot centre is 42 mm above that edge; the front mark is 72 mm above it. Calculate Rf and show how you obtained both travel distances.
Spot distance from baseline
Front distance from baseline
Rf and working
Nudge (only if you are stuck): Where did the spot and solvent start? Which offset must you subtract from both readings?
4. Explain
A sample contains soluble colourless substances. Describe the complete method for separating them and making the separated spots visible. Include the front mark and drying stages.
Prepare the paper and solvent, with reasons
Develop and finish in order
Explain the key precaution and when to locate
Nudge (only if you are stuck): Which steps separate the sample? Which step only reveals where its components ended up?
5. Calculate
After locating, a colourless sample shows two spots. Baseline, lower centre, upper centre and front are 1.0, 2.8, 5.2 and 7.0 cm above the bottom edge. Calculate both Rf values. Explain why the earlier blank appearance didn't justify discarding it, and what two revealed spots show.
Both Rf calculations
Initially blank paper and composition after locating
Nudge (only if you are stuck): Subtract the same baseline offset from every reading. What can travel without leaving a coloured stain?