Scientific Method Chemistry Tutorial

Key Concepts

• Scientific method refers to the process of thinking about scientific questions.
• This process of thinking about scientific questions includes:

  (a) making observations to accumulate information

  (b) deriving scientific laws by organising the information and looking for regularities or patterns

  (c) making an hypothesis to explain why the regularities or patterns exist

  (d) tesing the hypothesis by a suitable experiment and communicating the findings and probable explanations to others

• The scientific method is a cycle.

  By testing the hypothesis we make new observations which require us to look for patterns thereby formulating new laws which require new hypothesis that then need to be tested, etc.

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Observations

Seeing is NOT the same as observing.
To "see" is to use your eyes to perceive something, but to "observe" the same thing requires you to use as many of your senses as possible in order to really take notice of the thing.

Observation requires concentration and alertness.

The senses a Chemist uses to make observations are:

• sight

  (safety: wear eye protection in the Lab)

• smell

  (safety: gently waft the smell to your nose using your hand)

• hearing

  (safety: keep a suitable distance if safe to do so)

• touching

  (safety: only touch if considered safe to do so)

• tasting

  (safety: NEVER taste anything you found or produced in the Lab!)⁽¹⁾

Example of Observations: In a test tube, colourless dilute hydrochloric acid is added to a dark solid which is iron(2+) sulfide (iron(II) sulfide).
The following observations are made:

• sight :

  (a) bubbles appear in the solution originating at the surface of the iron(2+) sulfide (iron(II) sulfide)

  (b) the amount of solid iron(2+) sulfide (iron(II) sulfide) diminishes over time

• smell : the odour of rotten eggs is detected
• hearing : a fizzing sound may be heard
• touching : the test tube becomes warm
• tasting : never taste anything you found or produced in the Lab!

Observations also include making measurements.

Using the same example as the one above, the following measurements, additional observations, could be made:

• collecting the bubbles of gas and measuring its volume over time
• collecting samples of the gas-in-air mixture and measuring its concentration over time
• measuring the sound level over time⁽²⁾
• measuring the change in temperature of the solution in the test tube over time

Observations which are recorded are called scientific data.
This scientific data is essential for the next step in the process of the scientific method, that is, scientific data is essential for establishing scientific laws.

Scientific Laws

Deriving a scientific law requires that:

(a) the data (recorded observations) be organised

(b) the data be examined to determine whether there is a pattern

(a) Organising the Data: tables and graphs are commonly used to organise the data.

How you organise the data can influence the patterns you see in the data.

Example: 6 students added a small piece of solid iron(2+) sulfide (iron(II) sulfide) to dilute hydrochloric acid in a large test tube and recorded the volume of gas produced.

A table of all the results is shown below based on an alphabetical listing of the names of the students:

(b) Examine the organised data to see if there is a pattern

We can see a few possible patterns in the data:

(i) Students with names 5 letters long collected more gas than students with names only 4 letters long.

(ii) Students whose names start with "C" collected more gas than students whose names start with "J".

(iii) The amount of gas collected decreases the further along the alphabet the student's name occurs.

But which, if any of these patterns could help us predict the results of future experiments involving different people?

In order to find out, we need to set up a testable hypothesis, the next step in the scientific method.

Making an Hypothesis

An hypothesis is a statement of the possible answer to a scientific question we have asked.

In the example above we saw a number of different possible patterns in the data.
These patterns suggest the following possible questions:

(i) Do students with more letters in their name collect more gas?

(ii) Is the amount of gas collected dependent on the letters in a student's name?

For the first question a suitable hypothesis might be: "Students with longer names collect more gas"

For the second question a suitable hypothesis might be: "Student names that occur earlier in the alphabet collect more gas".

Testing the Hypothesis

Testing an hypothesis requires:

(i) the design of a suitable experiment

(ii) communicating the results of the experiment (in a lab report).

(i) Designing an Experiment to Test an Hypothesis

Hypothesis: "Students with longer names collect more gas"

Test: repeat the experiments using students with names beginning with "J", but who have different numbers of letters in their names, eg, Jo, Jan, John, James, Joshua, Janette

Possible results are shown in the table below:

The table has been organised using the increasing length of the names of the students.
The student with the shortest name has collected the most gas, but the student with the longest name has not collected the least amount of gas.

(ii) Communicating the Results

In our lab report we would conclude that there is no relationship between the number of letters in a student's name and the volume of gas collected.
We would suggest looking at the data again in order to see if there is a different pattern and therefore a different hypothesis that could be tested, as is discussed in the example below.

Worked Example of Using the Scientific Method in Chemistry

The observations from the original experiment involving Chris, Cindy, Clive, Jack, Jane and John were initially presented as a table listing the volume of gas collected by each student in alphabetical order.
This led to the hypothesis that the volume of gas collected was dependent on the length of a student's name.
On testing the hypothesis using a suitable experiment, the hypothesis was shown to be false.
We need to start the process of scientific method all over again:

(i) Making Observations:
Let us now look at the original data again, but this time, let's include the mass of iron(2+) sulfide (iron(II) sulfide) used by each student as shown in the table below:

(ii) Looking for patterns in the data:
If we now disregard the names of the students, we see a new pattern in the observations.
As the mass of iron(2+) sulfide (iron(II) sulfide) used in the experiment decreases, the volume of gas collected also decreases.
This raises the question, "Is more gas always collected if more iron(2+) sulfide (iron(II) sulfide) used?".

(iii) Making an hypothesis:
An hypothesis is a statement of the possible answer to a scientific question we have asked.
A possible hypothesis is, "The volume of gas collected is dependent on the mass of iron(2+) sulfide (iron(II) sulfide) used".

(iv) Testing the hypothesis:
A suitable experiment needs to be designed to test the hypothesis.
This experiment would require using the same volume of the same acid as before, but changing the amount of iron(2+) sulfide (iron(II) sulfide) added to the acid.
If it is found that the volume of gas collected does indeed increase if more iron(2+) sulfide (iron(II) sulfide) is used, then the hypothesis is supported and is found to be "true".⁽³⁾
If it is found that the volume of gas collected does not increase if more iron(2+) sulfide (iron(II) sulfide) is used, then the hypothesis is not supported and is found to be "false".
If the hypothesis is found to be false, the data needs to be re-examined to look for other patterns, then a new hypothesis will need to be made and tested.