The Aim ^🔗

What is the objective of your experiment?

An aim describes what you will be investigating (the purpose of the experiment). Keep it simple but specific. One sentence long.

e.g. The aim of this experiment is to investigate the relationship between [concentration/surface area/temperature] and the rate of reaction for [your reactants here].

The aim of this experiment is to investigate the relationship between surface area and the rate of reaction for calcium carbonate and hydrochloric acid.

The Hypothesis ^🔗

A prediction for the outcome of the experiment.

• It should be specific and testable
• It must make a prediction about the effect of your independent variable on your dependent variable.

e.g. I think that [your dependent variable here] will [increase/decrease] when the [your independent variable here] is [increased/descreased].

I think that the rate of reaction will be highest with calcium carbonate powder. For example, the time taken to produce 10ml of gas will be the lowest with calcium carbonate powder.

Independent Variable ^🔗

The variable that you will change throughout the experiment.

• You will only change one thing about one reactant.
• For Year 11 this will be one of: surface area, temperature, concentration or presence of a catalyst
• Where possible you should include the 3-5 increments you will use, plus the unit.

e.g. We will change the temperature of the hydrochloric acid. We will use 10C, 20C, 30C, and 60C.

Dependent Variable ^🔗

The variable being measured.

• It should have a well-defined endpoint (e.g. 10ml of gas)
• Include the equipment used to measure it.
• Include a unit.
• It is a way to indirectly measure the rate of reaction. The more quickly the endpoint is reached, the higher the rate of reaction.

e.g. We will measure the time taken to produce $10ml$ of carbon dioxide gas as an indirect measure of the rate of reaction.

Control Variables ^🔗

Things that you are keeping constant in between trials.

• Control variables allow a test to be fair
• Control variables allow a method to be reliable (consistent)
• Without control variables, you cannot be sure that the thing you are changing was the sole influence on your measurements. There may have been other influences.
• Include at least four control variables in your report and explain how you will control them and how they would influence your measurements if not controlled.

For example:

• We will use the same volume of hydrochloric acid each time.
  • How: We will measure it with a measuring cylinder (in mls).
  • Why: If the volume of acid used each time was different there would be a different number of hydrochloric acid molecules available to react. This would affect the number and frequency of of possible collisions and therefore the rate of reaction.

Method ^🔗

A method should be a sequential set of steps that any uninformed person could follow to perform the exact same experiment.

• Give a list of necessary equipment (be specific about beaker sizes etc.)
• Use numbered, short, steps
• Give directions as commands.
  • “Measure 3g of calcium carbonate powder with a balance into a beaker.”
• Some steps may be repeated while the independent variable is changed.
  • “Repeat steps 3-7 three times for each of large chips, small chips and powder of calcium carbonate.”
• Indicate when something is to be recorded and how to calculate the relevant average.
• Indicate if equipment needs to be washed/reset between trials.

Data + Results ^🔗

• Design a table to record your results before you start the experiment/whakamātau.
• Think about how many trials you will do, as well as an average.
• This is also a place to make a note of anything unusual that occurred during your experiment, or if anything went wrong etc.

A table might look something like this:

Calculations ^🔗

When calculating an average, you should give an example of how you did it so that another Scientist can see the process.

Calculating an Average: Add up all your trials and divide by the number of trials.

E.g. To calculate the averages for our results we took the three trials, added them together and divided by three like so: (3.5 + 3.0 + 3.3) / 3 = 3.27s

Graphs ^🔗

• You will draw a graph by hand in the test.
• A graph should have the following:
  • Independent (thing you are changing) on the x-axis
  • Dependent (thing you are measuring) on the y-axis
  • Plot the averages
  • A title
    • Describe the aim of the experiment. E.g. “Relationship between Surface Area and Rate of Reaction with Antacid Tablets”
  • X and Y axis labels + units
  • Data points indicated with crosses
  • A smoooth line of best fit
  • DO NOT JOIN THE DOTS
  • X and Y axes starting at zero
  • Even scale on the X and Y axes

Conclusion ^🔗

• Link your aim and hypothesis to the data you gathered.
• Summarise your data by stating the trend.
• Give an example comparison of two data points.
• Explain whether this supported your hypothesis or not and whether you achieved your aim.

e.g. In our experiment we investigated [your aim here] and we found that when [your data summary here]. This is reflected in our data, for example [your example data here]. This [supports/does not support] our hypothesis that [your hypothesis here].

Discussion/Evaluation ^🔗

• Discuss any mistakes that were made (past tense)
• Discuss improvements/changes to your method that were made (past tense)
• Discuss future improvements that could be made to your method
• Discuss what your findings suggest about what you are modelling - this is where you bring in some Science and research!.
  • For Year 11 this means a discussion of collision theory and rates of reaction specific to this experiment.
  • Consider writing the following:
    • A description of the how a reaction occurs (collision + activation energy + orientations)
    • A description of how your independent variable affects collision theory. This would include effects on the number of collisions, probability of successful collisions where appropriate.
    • A description of your data trend compared to accepted theories (what you got taught in class)
    • A description of how your measurement of something (e.g. gas) is a vaild way to measure the rate of reaction. E.g. Gas production is a direct result of a successful collision, and is therefore valid.
• Discuss the reliability of your data
• Discuss the validity of your method

Reliability ^🔗

• What does it tell you?
  • The extent to which the results can be reproduced when the research is repeated under the same conditions.
• How is it assessed?
  • By checking the consistency of results between each trial of the increments of the independent variable.
• How does it relate to validity?
  • A reliable measurement is not always valid: the results might be reproducible, but they’re not necessarily correct.

e.g. Looking at our results we can see that each trial of the different increments of our independent variable are similar to each other. This means that our dependent variable is well controlled. These results should therefore be reproducible by other scientists. However, this does not indicate that these results are correct or valid.

If you are getting a wide variety in results, you may need to re-work your method by adding further control variables or clearer instructions so the trials are closer together.f

Validity ^🔗

• What does it tell you?
  • The extent to which the results really measure what they are supposed to measure (model vs real world).
• How is it assessed?
  • By checking how well the results correspond to established theories and other measures of the same concept. Do your results match previous research/experiments? Do they match the theory you learned about in class?
  • By checking that you have sufficient control variables that you are confident the only thing that could have affected the rate of reaction was your independent variable.
• How does it relate to reliability?
  • A valid measurement is generally reliable: if a test produces accurate results, they should be reproducible.

e.g. Theories, research and past experiments show that when the surface area of a reactant is increased, the rate of reaction is also increased. Our data shows the same trend. This indicates that our experiment is sufficiently controlled and that we are actually measuring the influence of surface area on the rate of reaction.

This experiment is actually measuring the rate of reaction because we controlled the other factors that can impact the rate of reaction (concentration, temperature, and presence of a catalyst). We can be relatively certain that surface area was the main influence on the rate of reaction in our experiment.