L5 - Experimental Design

Activate Learning 

Gather in your groups and look at the EXAMPLE 6 below. 

Read the proposed answer below and note down your observations of what is found in each of the following sections:
(a) Equipment list

(b) Diagrams
(c) Procedure
(d) Analysis of data
(e) Risk Assessment and Management  

Promote thinking and discussion 

Discuss, in your groups, how you should write Section 2: METHODS of your own project. 

Facilitate Demonstration of Learning 

After your discussion, pen down the Section 2: METHODS in your proposals. Include all necessary components that you should find in the model answer.  

If you need to draw or edit a picture, you can download and use MacPaint
http://paintbrush-mac.en.softonic.com/mac/download

Monitor and provide feedback

Your teacher will provide you with the feedback of Section 2: METHODS section after you have submitted your draft proposals for review.

EXAMPLE 6 

A student wanted to find out what temperature is the best for making the biggest crystals. (The aim)

His/her hypothesis is that the lower the temperature, the bigger is the crystal grown.

The variables are: 

The independent variable is temperature.

The dependent variable is the mass of copper sulfate crystals.

The constants are:

(a) the concentration of the copper sulfate solution used

(b) the total volume of the copper sulfate solution used

(c) the humidity of the environment above the beaker

(d) the mass of the seeding crystal

(e) the shape of the seeding crystal  

Equipment list:  

-       clean beaker (250 ml) x 10

-       copper sulfate in powder form (250 g) 

-       stirrer x 1 

-       Bunsen burner x 1 

-       Lighter x 1 

-       Weighing machine x 1

-       Magnifying glass x 1

-       Silica gel x 10 packets of 50g each 

-       refrigerator (-10 degree Celcius to room temperature) x1 

-       incubator oven ( room temperature to 50 degrees Celcius) x1 

-       chopsticks x 100

      Diagrams

Fig. 2.1 Experimental setup

Procedure:

1.    Set up the experiment as shown in the diagram above.

2.    Pour 50 grams of copper sulfate crystals into a beaker of 200 ml of distilled water and dissolve it using a stirrer.

3.    Ensure that the concentration of copper sulfate is saturated, heat the beaker using a Bunsen flame so that we can dissolve the maximum amount of copper sulfate.

4.    Stop the heating process when we observe that the crystals cannot dissolve any further due to heating and stirring. 

5.    Pour equal amounts of the copper sulfate solution into 6 different beakers of different amounts. (e.g. 25 ml each)

6.    Make sure that the seeding crystals used to make the big crystals are of the same shape by using a magnifying glass to inspect.

7.    Make sure that the seeding crystals used to make the big crystals are of the same mass by using a weighing machine.

8.    Place the seeding crystals into the 6 different beakers.

9.    Place the 6 different beakers into the refrigerator and the incubator ovens set according to the temperatures specified.

10. Ensure that the humidity of the space above the beakers remains the same, place a packet of moisture absorber (silica gel) in each of the refrigerator and the oven so as to make sure that the humidity is low. This is to make sure that there is no condensation of water vapor in the refrigerator and oven into the beaker of copper sulfate.

11. Wait patiently for a period of 5 days without disturbing the 6 beakers of copper sulfate solution.

12. Remove the beakers from the refrigerators or ovens and remove the seeded crystal using a pair of chopsticks carefully after 5 days.

13. Measure the final mass of the grown crystal using a weighing machine.

14. Repeat the experiment again using a similar setup and measure the average mass of the grown crystal again.

Analysis of data:

15. Tabulate the data and calculate the average mass of the grown crystal. 

Table 2.1: Table of values for average mass of crystals against the temperature.

16. Plot a graph of the average mass of the crystal against the temperature in which it is grown.

Fig. 2.2 Graph of average mass of crystal against temperature. 

17. From the graph, we can find out which temperature can make the biggest crystals. (The aim)