A student investigated the effect of acid concentration on the rate of diffusion in agar jelly. The student was given three test-tubes containing bromothymol blue indicator in agar jelly. Bromothymol blue is a blue indicator that turns yellow in the presence of an acid. The student used this method: Step 1 label three beakers A1, A2 and A3 Step 2 put $$\(20 \mathrm{~cm}^{3}\)$$ of 1 mol per $$\(\mathrm{dm}^{3}\)$$ hydrochloric acid solution into beaker $$\(\mathbf{A 1}\)$$ Step 3 put $$\(2 \mathrm{~cm}^{3}\)$$ of 1 mol per $$\(\mathrm{dm}^{3}\)$$ hydrochloric acid solution into beaker A2 Step 4 add $$\(18 \mathrm{~cm}^{3}\)$$ of distilled water to the hydrochloric acid solution in beaker A2 Step 5 use a clean syringe to transfer $$\(2 \mathrm{~cm}^{3}\)$$ of the solution from beaker A2 to beaker A3 Step 6 add $$\(18 \mathrm{~cm}^{3}\)$$ of distilled water to beaker $$\(\mathbf{A 3}\)$$ Table 1.1 shows the final concentrations of the hydrochloric acid solution in each beaker. In an experiment, a student cut different-sized cubes of agar containing bromothymol blue indicator. The student placed the cubes in hydrochloric acid and measured the time taken for each cube to become yellow. The results are shown in Table 1.2. (i) Complete Table 1.2 by calculating the volume of the 4 mm cube. \begin{tabular}{l} z \\ \hline \end{tabular} Write your answer in Table 1.2. \begin{tabular}{l} z \\ \hline \end{tabular} \begin{tabular}{l} 느 \\ \hline \end{tabular} (ii) Plot a line graph on the grid of the length of the cube sides against the time taken for the cubes to become yellow. (iii) Use your graph to estimate the time taken for a cube with a side length of 3 mm to become yellow. Show on your graph how you obtained your answer. .......................................................... S (iv) State two variables that should have been kept constant in this investigation. 1 ..................................................................................................................................... ....................................................................................................................................... . 2 ..................................................................................................................................... ....................................................................................................................................... .

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