Vegetables，such as carrots，contain sugars． Potassium manganate（VII）solution can be used to identify the presence of sugars． The sugars change the colour of the potassium manganate（VII）solution from purple to colourless． You will measure the time taken for potassium manganate（VII）solution to turn colourless with sugar solutions of known concentration．You will use the results to estimate the concentration of sugars in a carrot extract． You are provided with the materials shown in Table 1．1． Table 1.1 If any solution comes into contact with your skin，wash off immediately with cold water． It is recommended that you wear suitable eye protection and wear gloves to protect your hands when using $$\(\mathbf{A}\)$$ and $$\(\mathbf{K}\)$$ ． You will need to： －prepare different concentrations of sugar solution －record the time taken for $$\(\mathbf{K}\)$$ to become colourless（end－point）for each of the different concentrations of sugar solution and for the carrot extract，C －use your results to estimate the concentration of sugars in the carrot extract，C． You will need to use proportional dilution to make five different concentrations of sugar solution． You will need to prepare $$\(10 \mathrm{~cm}^{3}\)$$ of each concentration，using $$\(\mathbf{S}\)$$ and $$\(\mathbf{W}\)$$ ． Table 1.2 shows two of the concentrations of sugar solution you will use and how to prepare them． Decide which three other concentrations of sugar solution you will use． Complete Table 1.2 to show how you will prepare the other concentrations of sugar solution you will use. Table 1.2 Carry out step 1 to step 11 . step 1 In the beakers provided, prepare the concentrations of sugar solution, as shown in Table 1.2. step 2 Label the test-tubes with the concentrations of sugar solution prepared in step 1. step 3 Put $$\(1 \mathrm{~cm}^{3}\)$$ of $$\(1.0 \mathrm{~mol} \mathrm{dm}^{-3}\)$$ sugar solution into the appropriately labelled test-tube. step 4 Repeat step 3 with each of the other concentrations of sugar solution. step 5 Put $$\(1 \mathrm{~cm}^{3}\)$$ of $$\(\mathbf{A}\)$$ into each of the test-tubes. Shake gently to mix. The reaction will start as soon as you put $$\(\mathbf{K}\)$$ into the test-tubes (step 6). Keep the timer running continuously until the end of step 7. step 6 Put $$\(1 \mathrm{~cm}^{3}\)$$ of $$\(\mathbf{K}\)$$ into each of the test-tubes and start timing. Shake gently to mix. step 7 Measure the time taken for each concentration to reach the end-point. As each end- point is reached record the time taken in (a)(ii). If an end-point has not been reached after 600 seconds, record the time as 'more than 600'. (ii) Record your results in an appropriate table. step $$\(8 \quad\)$$ Label a test-tube $$\(\mathbf{C}\)$$ and put $$\(1 \mathrm{~cm}^{3}\)$$ of $$\(\mathbf{C}\)$$ into this test-tube. step 9 Put $$\(1 \mathrm{~cm}^{3}\)$$ of $$\(\mathbf{A}\)$$ into the test-tube. Shake gently to mix. step 10 Put $$\(1 \mathrm{~cm}^{3}\)$$ of $$\(\mathbf{K}\)$$ into the test-tube and start timing. Shake gently to mix. step 11 Measure the time taken to reach the end-point. Record the time taken in (a)(iii). (iii) State the time taken to reach the end-point for $$\(\mathbf{C}\)$$. time taken ..................................................... (iv) Estimate the concentration of sugars in $$\(\mathbf{C}\)$$. concentration of sugars in $$\(\mathbf{C}\)$$ ....................................... $$\(\mathrm{moldm}^{-3}\)$$ (v) Suggest how the procedure could be modified to improve the accuracy of your estimate in (a)(iv). ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . (vi) A student used the same procedure to compare the concentration of sugars in three vegetables: carrot, potato and onion. State one variable that needs to be standardised in the procedure. ....................................................................................................................................... . ................................................................................................................................. (vii) Suggest how the student could extend this investigation to estimate the concentration of starch in a vegetable extract. ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . .................................................................................................................................

Answer:

Knowledge points:

Solution: