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Question 1
In paper chromatography, which of the following correctly identifies the stationary phase and mobile phase?
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Correct answerCorrect!Incorrect
AStationary phase: absorbent paper; Mobile phase: liquid solvent
Step-by-step walkthrough
Choose a solution method
Method #1Direct Approach
Step 1: Define the two phases
In chromatography, the stationary phase is the material that stays still, while the mobile phase is the material that moves through it carrying the substances.
Step 2: Match to paper chromatography
In paper chromatography specifically, the absorbent paper does not move — it is the stationary phase. The liquid solvent travels up the paper by capillary action — it is the mobile phase.
Step 3: Choose the correct answer
The correct answer is: Stationary phase: absorbent paper; Mobile phase: liquid solvent. The sample mixture is neither a phase — it is what gets separated by the two phases.
Method #2Process of Elimination
Step 1: What is being asked?
The question asks us to correctly pair the stationary and mobile phases specifically in paper chromatography.
Step 2: Eliminate reversed options
'Stationary phase: liquid solvent; Mobile phase: absorbent paper' is wrong — the solvent moves, so it cannot be stationary. The paper does not move, so it cannot be the mobile phase.
Step 3: Eliminate options involving the sample
'Stationary phase: the sample mixture; Mobile phase: absorbent paper' and 'Stationary phase: liquid solvent; Mobile phase: the sample mixture' are both wrong — the sample mixture is what gets separated, not a phase in the system.
Step 4: Select the correct answer
The remaining option — 'Stationary phase: absorbent paper; Mobile phase: liquid solvent' — is correct and matches the definitions.
Question 2
A student runs a paper chromatography experiment. The solvent front travels 9.0 cm from the baseline. A red spot travels 6.3 cm from the baseline. What is the Rf value of the red substance?
No clue? Show me the answer
Correct answerCorrect!Incorrect
A0.70
Step-by-step walkthrough
Choose a solution method
Method #1Direct Approach
Step 1: Recall the Rf formula
The Rf value is calculated using: $R_{f} = \frac{distance travelled by substance}{distance travelled by solvent front}$
Step 2: Substitute the values
Distance travelled by the red spot = 6.3 cm, distance travelled by solvent front = 9.0 cm. $R_{f} = \frac{6.3}{9.0}$
Step 3: Calculate the result
$R_{f} = \frac{6.3}{9.0} = 0.70$ The Rf value is 0.70 (no units, since it is a ratio).
Method #2Process of Elimination
Step 1: What is being asked?
We need to calculate the Rf value, which must be between 0 and 1 since a substance can never travel further than the solvent front.
Step 2: Eliminate values greater than 1
1.43 is greater than 1, which is impossible for an Rf value. This would suggest the substance travelled further than the solvent, which cannot happen.
Step 3: Check the calculation for remaining options
0.63 would come from $\frac{6.3}{10}$ (wrong denominator). 0.57 would come from $\frac{6.3}{11}$ (also wrong). Only 0.70 comes from $\frac{6.3}{9.0}$ , which uses the correct values.
Step 4: Select the correct answer
The correct Rf value is 0.70, calculated correctly as $\frac{6.3}{9.0}$ .

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Step-by-step walkthrough

Step 1: Define the two phases

Step 2: Match to paper chromatography

Step 3: Choose the correct answer

Step 1: What is being asked?

Step 2: Eliminate reversed options

Step 3: Eliminate options involving the sample

Step 4: Select the correct answer

Step-by-step walkthrough

Step 1: Recall the Rf formula

Step 2: Substitute the values

Step 3: Calculate the result

Step 1: What is being asked?

Step 2: Eliminate values greater than 1

Step 3: Check the calculation for remaining options

Step 4: Select the correct answer

12 more questions in this topic