Using the given figure, the ratio of R_f values of sample A and sample C is x× 10⁻². Value of x is __________.

Solution

Chemistry ma’am · 4 steps

Read each spot's distance from the base line, divide by the solvent front, then take the ratio.

1. What Rf means. R_f is the distance moved by the spot divided by the distance moved by the solvent front. Both distances are measured from the base line.

   R_f = (distance moved by the substance)/(distance moved by the solvent front)

2. Read the figure. The solvent front is at 12.5 cm. Sample A is at 5.0 cm, so R_f(A) = 5.0/12.5 = 0.4. Sample C is at 10.0 cm, so R_f(C) = 10.0/12.5 = 0.8.
3. Take the ratio. R_f(A)/R_f(C) = 0.4/0.8 = 0.5 = 50 × 10⁻². The solvent front cancels, so this is also 5.0/10.0.
4. So. The ratio is 50 × 10⁻², so x = 50.

The common slip: 200. Dividing C by A instead of A by C gives a ratio of 2, which is 200 × 10⁻², so x comes out as 200.

The idea to keep. For the same plate, the solvent front distance is common to every spot, so a ratio of R_f values is just the ratio of the distances the spots moved.

Answer from the NTA final answer key. Solution by PrepWiser.