You are going to investigate the effect of acid concentration on the rate of diffusion. Bromothymol blue is an indicator that turns yellow in the presence of an acid. Read all the instructions but DO NOT DO THEM until you have drawn a table for your results in the space provided in 1(a)(iii). You should use the safety equipment provided while you are doing the practical work. Step 1 Label three beakers A1, A2 and A3. Step 2 Add $$$20 \mathrm{~cm}^{3}$$$ of 1 mol per $$$\mathrm{dm}^{3}$$$ hydrochloric acid solution to beaker $$$\mathbf{A 1}$$$. Step 3 Add $$$2 \mathrm{~cm}^{3}$$$ of 1 mol per $$$\mathrm{dm}^{3}$$$ hydrochloric acid solution to beaker $$$\mathbf{A 2}$$$. Step 4 Add $$$18 \mathrm{~cm}^{3}$$$ of distilled water to the hydrochloric acid solution in beaker $$$\mathbf{A} 2$$$ and mix well. 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 $$$\mathbf{A} 3$$$ and mix well. 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. Write your answer in Table 1.2. (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 .................................................................................................................................... ....................................................................................................................................... .

Biology

IGCSE&ALevel

CAIE

Exam No：0610_s24_qp_52 Year：2024 Question No：1(b)

Answer:

Knowledge points:

4.1.1 List the chemical elements that make up: – carbohydrates – fats – proteins

4.1.10 Describe the roles of water as a solvent in organisms with respect to digestion, excretion and transport

4.1.2 State that large molecules are made from smaller molecules, limited to: – starch and glycogen from glucose – cellulose from glucose – proteins from amino acids – fats and oils from fatty acids and glycerol

4.1.3 Describe the use of: – iodine solution to test for starch – Benedict’s solution to test for reducing sugars – biuret test for proteins – ethanol emulsion test for fats and oils – DCPIP test for vitamin C

4.1.4 Describe the use of: – iodine solution to test for starch – Benedict’s solution to test for reducing sugars – biuret test for proteins – ethanol emulsion test for fats and oils – DCPIP test for vitamin C

4.1.5 Describe the use of: – iodine solution to test for starch – Benedict’s solution to test for reducing sugars – biuret test for proteins – ethanol emulsion test for fats and oils – DCPIP test for vitamin C

4.1.6 State that water is important as a solvent

4.1.7 Explain that different sequences of amino acids give different shapes to protein molecules

4.1.8 Relate the shape and structure of protein molecules to their function, limited to the active site of enzymes and the binding site of antibodies

4.1.9 Describe the structure of DNA as: – two strands coiled together to form a double helix – each strand contains chemicals called bases – cross-links between the strands are formed by pairs of bases – the bases always pair up in the same way: A with T, and C with G (full names are not required)

Answer:

Knowledge points:

Solution:

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