1. 1 Solving Problems in Science International Junior Science Olympiad (IJSO) Dr. Yu-San Cheung yscheung@cuhk.edu.hk Department of Chemistry The Chinese University of Hong Kong

2. 2 Observation  Hypothesis  Experiment  Analysis  Theory  Prediction  Experiment Modifying theory as needed Law Scientific Method

3. 3 Precision vs. Accuracy Precision( 精密度 ) -representing the agreement between repeated measurements of the same quantity Accuracy( 準確度 ) -representing the agreement between a measured value and the true quantity

4. 4 Significant figure: Multiplication and division: keep the smaller number of significant figure Decimal place: Addition and subtraction: keep the smaller number of decimal place

5. 5 Exercise Determine the answer for (a) to (f) below. Use the correct number of significant digits in your answer. a.7.2 mm x 1.56 mm = b.99.5 cm 2 x 0.0084 cm = c.63.6 g/ 2.7 cm 3 = d.288 g/16.9 cm 3 = e.0.001 g + 5.3 g + 162 g = f.32.58 cm 3 – 5.2 cm 3 =

6. 6 Control Experiment A method of scientific investigation to demonstrate a cause and effect hypothesis. For example, a phenomenon occurs after a certain treatment is given to a subject, and that the phenomenon does not occur in the absence of the treatment.

7. 7 Variable in Control Experiment Dependent variable Quantity to be measured; Quantity which is thought to be affected during the experiment; Results of the experiment. Independent variable Quantity to be varied; Quantity which is thought to affect the dependent variable(s); Quantity which can be manipulated or controlled. Controlled variable Quantity kept constant or unchanged.

8. 8 Experiment Set-up Control Group vs Experiment Group Control Group Set-up Procedures Control Variables Experiment Group Set-up Procedures Control Variables Independent Variables

9. 9 A Photosynthesis( 光合作用 ) Problem The following experiment is designed to find out whether light is necessary of photosynthesis. A.What is the hypothesis of this experiment? B.If starch is present in region A but absent in region B after exposing the plant to sunlight for several hours, what would your conclusion be? C.Which region is the control? Explain briefly.