Planning & Designing Experiment Information

HOW TO PLAN AN EXPERIMENT

What is Planning and Designing ?
This is where the student design an experiment to test a hypothesis .
The student may carry out the experiment although this is not necessary .

What is a hypothesis ?
A hypothesis is a intelligent guess .

How do you come up with an hypothesis ?
The student is given a statement describing a situation or a problem . The student is asked to suggest an explanation for the situation or problem . The explanation or hypothesis must be a one sentence stated in a positive way .
e.g. You are given a colourless liquid which has a sour odour .
Hypothesis : The liquid is an acid .

What’s after the hypothesis ?
The student comes up with an aim . The aim must be to prove or determine something . It must be based on the hypothesis .
e.g. To identify an unknown liquid as an acid .
You then come up with an method to test the hypothesis .

How do you determine a method ?
The method must have three elements .
1.    It must be simple and easy to carry out .
2.    The results must be reproducible . that is every time it is carried out the same results are obtained .
3.    The results must be clear and definite .

What to be considered in designing the experiment ?
There are in every experiments , factors . Factors affect the outcome of experiments .
Some factors cannot be changed and those which can are called variables .
Factors include :

Light
Temperature
Concentration
Surface area
Volume
Mass
Length
Time

More on Variables
Variables are of three types
1.    Controlled – not changed
2.    Manipulated – changed by the experimenter
3.    Responding – changes by the conditions of the experiment

E.g. If I was to react an acid with a metal . The acid will dissolve the metal . If I was to keep the concentration and amount of acid and metal constant and change the temperature the variable that respond would be the time ( the time taken for the metal to completely disappear ) .

In writing up a P&D experiment you must state all the variables and which are controlled , manipulated and responding . Only one variable may be manipulated at a time .
At times you may not change any variable in an experiment , this is called a control .

Types of Method
There are three formats in which we can do an P&D experiment .
1.    You can do a Expected vs. Actual Format
You can set up a table as follows

Test	Expected	Actual	Inference
Add a few drops of indicator	The indicator will change to blue	The indicator changed to red	The substance is not an alkali

The test is the test which you will carry out . The Expected is what you would expect the results to be if your hypothesis is true . The Actual is what really occurred . The Inference is what you deduce by the actual results .

2. You can do a Comparison Format
You set up a table as follows

Test	Hydrochloric acid	Liquid A	Inference
Add sodium carbonate	effervescence occured	effervescence occured	A could be an acid
Add blue litmus	changed to red	changed to red	A could be an acid

You test a known substance and then the unknown an compare the results .

3. You can do a Normal Format
Just carry out the experiment and then refer to supporting material to draw conclusions .

What is next ?
If you are not required to carry it out you stop after method and just write your Discussion about the method you have chosen .

If you carry out the experiment the Discussion will not only include the method but the results as well . Please explain the results .
The conclusion will be whether the hypothesis is true or not .It is based off the inferences .

Outline of P&D experiment

Title
Problem Statement
Hypothesis
Aim
Outline : Factors & Variables ; Which are controlled and manipulated ? Which will respond ?
Apparatus
Method
Results
Discussion : What led you to the hypothesis ? Why this method ? How did you control the variables ?
Sources of Error
Conclusion

Example 1
Title : Planning & Designing 4

Problem Statement : You are given a silver looking pebble and asked to determine what this substance might be .

Hypothesis : The substance is a metal

Aim : To identify an unknown as a metal

Outline : If the substance is a metal we have to look at the properties of metals and carry out tests for these properties . All the factors will remain constant and we will Just perform different tests .

Method :
Divide the substance into several small but equal pieces
Add acid - metals will effervesce
Place in a circuit - metals will conduct an electric current

Discussion : The substance is silver in colour which is indicative of metals .

Example 2
Title : Planning & Designing 5

Problem Statement :
You are given a salt and asked if the salt will dissolve in water more at high temperatures .

Hypothesis : The salt will dissolve more at room temperature .

Aim : To determine the solubility of a salt at different temperatures .

Outline :
The factors to be considered are ; the amount of salt , the volume of water , he temperature , the time taken to dissolve , We control the volume of water , amount of salt and time to dissolve . We manipulate the temperature . The amount of salt that remains undissolved is responding .

Method :
Weigh out four equal amounts of the salt . Measure out four equal volumes of water . Prepare the water to the following temperatures , 0 degrees Celsius ( use ice ) , room temp 30 degrees Celsius , 60 degrees Celsius ( warm slightly ) and 90 degrees Celsius ( boil ) .

Place the salt in each container of water and stir for 20 seconds . Immediately pour the solution through a filter paper . Allow the residue to dry and reweigh .

Discussion : The one with the highest mass was most insoluble .