Investigation - Solution Colour and Ion Concentration
Aim: To investigate whether solution colour can be used to reliably determine the concentration of coloured ions in a solution. Hypothesis: the concentration of permanganate ions in the solution is inversely proportional to the percentage transmission of light through the solution.
Dependent variable: concentration of permanganate ions.
Independent variable: percentage transmission of light through the solution.
20 ml of 0.00100 molL-1 potassium permanganate
20 ml distilled water
6 identical test tubes
1 Test tube rack
1 plastic pipette
10 ml measuring cylinder
1. Measure 5 ml of potassium permanganate with the measuring cylinder, place this into the 1st test tube. Then measure 2 ml of distilled water with a plastic pipette, also place in the 1st test tube. Stir the solution gently with the pipette to ensure that the potassium permanganate is evenly diffused through the solution. 2. Repeat step 1, but this time put 4 ml of potassium permanganate and 3 ml of distilled water instead into the 2nd test tube. Keep repeating step 1, with 4ml(KMnO4) and 3ml(H2O), 3ml(KMnO4) and 4ml(H2O), 2ml(KMnO4) and 5ml(H2O), 1ml(KMnO4) and 6ml(H2O), 0.5ml(KMnO4) and 6.5ml(H2O). Place these solutions in separate test tubes and arrange the solutions in chronological order with descending concentration. 3. Label each test tube so they don’t get mixed up.
4. Measure 7 ml of distilled water with measuring cylinder and place into the 7th test tube, this is used for calibration. 5. Calibrate the photometer by placing the test tube with distilled water in it, adjust the scale to 100% by pressing then calibrate button. 6. Place each of the 6 test tubes one by one into the photometer, record down the percentage transmission of light readings in a table, and repeat this step 3 times to complete 3 trials. 7. Finally, measure 7ml of the potassium permanganate with unknown...
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