Activated charcoal is a form of carbon with a very high surface area. It can be used to remove impurities from mixtures. It does this by a process called adsorption, where particles of the impurity bond (adsorb) to the activated charcoal surface. A student wanted to determine the ability of activated charcoal to adsorb a blue dye (the impurity) from aqueous solution. The equation that links the mass of activated charcoal with the amount of blue dye adsorbed is shown. log (D/m) = A + b log [X] D = difference in concentration of dye (in g dm⁻³) before and after adsorption m = mass of activated charcoal (in g) [X] = final concentration of dye (in g dm⁻³) after adsorption A and b are constants The student used the following procedure to investigate the ability of activated charcoal to adsorb a blue dye from an aqueous solution. • Place a 50.0 cm³ sample of a 25.00 g dm⁻³ solution of blue dye in a conical flask. • Add a weighed mass of activated charcoal to the flask. • Stir the contents of the flask for three minutes and then leave for one hour. • Filter the mixture. • Determine the final concentration of the blue dye, [X], by colorimetry. • Repeat the procedure using different masses of activated charcoal.

1. (a)The final concentrations of blue dye after carrying out the procedure, [X], are shown in the table.
2. (a)(i)Process the results to complete the table. Record your data to two decimal places. mass of | initial | final | difference in | D | log(D/m) | log [X] activated | concentration | concentration | concentration | -- | --------- | --- charcoal, m | of blue dye | of blue dye, [X] | of blue dye, D | m | | /g | /g dm⁻³ | /g dm⁻³ | /g dm⁻³ | | | ---|---|---|---|---|---|--- 0.20 | 25.00 | 0.96 | | 120.20 | 2.08 | 0.25 | 25.00 | 0.69 | | 97.24 | 1.99 | 0.30 | 25.00 | 0.60 | | 81.33 | 1.91 | 0.35 | 25.00 | 0.41 | | 70.26 | 1.85 | 0.40 | 25.00 | 0.33 | | 61.68 | 1.79 | 0.45 | 25.00 | 0.27 | | 54.96 | 1.74 | 0.50 | 25.00 | 0.23 | | 49.54 | 1.69 | 0.55 | 25.00 | 0.20 | | 45.09 | 1.65 | 0.60 | 25.00 | 0.17 | | 41.38 | 1.62 |[3]
3. (a)(ii)By considering the data in the first three columns, state the effect of increasing the mass of activated charcoal, m, on the amount of adsorption that occurs. Explain this effect.[2]
4. (b)Plot a graph on the grid to show the relationship between log (D/m) and log [X]. Use a cross (x) to plot each data point. Draw the straight line of best fit.[2]
5. (c)Circle the most anomalous point on the graph. Suggest a reason why this anomaly may have occurred during the experimental procedure.[2]
6. (d)(i)Use the graph to determine the gradient of the best-fit line. State the co-ordinates of both points you used in your calculation. Determine the value of the constant b. co-ordinates 1 ...................................... co-ordinates 2 ...................................... gradient = ...................................... b = ......................................[2]
7. (d)(ii)Use the graph to determine a value for A. A = ......................................[1]

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