the solvent moves 9.0 cm
Calculate the R value for the colour from flower B.
Use the equation: R = distance moved by colour / distance moved by solvent
How to approach this question
1. Identify the "distance moved by colour" from the information provided.
2. Identify the "distance moved by solvent" from the information provided.
3. Substitute these two values into the given equation for the R value.
4. Calculate the result.
Full Answer
R = 7.2 cm / 9.0 cm
R = 0.8
The R value is a ratio that compares the distance travelled by a substance to the distance travelled by the solvent front. The formula is given:
R = distance moved by colour / distance moved by solvent
From the question:
- Distance moved by colour (from flower B) = 7.2 cm
- Distance moved by solvent = 9.0 cm
Substitute the values into the equation:
R = 7.2 / 9.0
R = 0.8
The R value has no units because it is a ratio of two distances.
Common mistakes
✗ Inverting the fraction (dividing 9.0 by 7.2). The R value must be less than 1.
✗ Calculation errors.
✗ Giving units for the R value.
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