Presentation on theme: "Planning an experiment & writing an experimental report."— Presentation transcript:
Planning an experiment & writing an experimental report
Plan When you are planning your experiment you should explain what you are trying to find out – this is the AIM of the experiment. Remember to mention what you are changing and what you are trying to find out.
Plan make sure the experiment is FAIR by changing only one variable – the is called the input variable or independent variable all the other variables should be unchanged – we say these are the controlled variables
Plan decide what you are going to MEASURE as the result of the experiment – this is called the outcome variable or dependent variable
Plan Use a ruler and a pencil to draw a LABELLED DIAGRAM diagram of the experiment Describe of how you will carry out your experiment and make sure you include any additional equipment or chemicals which you have not included in your diagram.
Safety Before you start your experiment you should discuss your plan and safety considerations with your teacher. While you are carrying out experiments your teacher will check that you are working safely.
Results During the experiment you should record your observations/measurements/results Tables of results should be drawn using a ruler and pencil. The table should have suitable headings and units.
Results Graphs should be plotted on squared graph paper again using a pencil and a ruler. The input variable (what you changed) should go along the x-axis and the outcome variable (what you measured as the result of the experiment) should go along the y-axis. Use a ruler to draw a line of best fit or draw a curve of best fit as best you can.
Conclusion Your conclusion should mention the connection (if any) between the input variable (what you changed) and the outcome variable (what you measured as the result of the experiment).
Evaluation Look at the results – are they as you expected? Maybe you could have done something differently. How could you improve your experiment? Did you control all the variables so you only changed one thing? Did you plan your experiment correctly to allow you to investigate what you intended to investigate? Did you use the correct equipment? Was the equipment available to you accurate enough to allow you to measure accurately? Was there some factor which you found difficult to control?
Example of Pupil Plan The task set: When acids react with (neutralise) alkalis, heat energy is released and a rise in temperature can be observed. You are being asked to investigate how the concentration of acid affects the size of the temperature rise. What are the input variable and outcome variable for this task?
Example of Pupil Plan concentration of acid = input variable size of the temperature rise = outcome variable
Example of Pupil Plan Plan I am only going to change the concentration of the acid. I will use 1 mol/l hydrochloric acid, 1.5 mol/l hydrochloric acid and 2 mol/l hydrochloric acid. Does this alter what the correct variable?
Example of Pupil Plan Plan Yes, this is correct so far. The concentration of the acid is going to be altered. concentration of acid = input variable
Example of Pupil Plan Plan I will keep everything else the same Same type of acid (hydrochloric acid) Same volume of acid (20cm 3 ) Same type of alkali (sodium hydroxide) Same concentration of alkali (2 mol/l) Same volume of alkali (20cm 3 ) Is this list complete?
Example of Pupil Plan Plan Yes, all the controlled variables are listed.
Example of Pupil Plan Measurements/observations Which is the best? (a) I will measure the temperature rise (b) I will measure the temperature before and then measure the temperature after 10 minutes (c) I will use a thermometer to measure the temperature before mixing the acid and alkali and measure the highest temperature after the chemicals are mixed
Example of Pupil Plan Measurements/observations (a) you need to subtract so that you can ‘calculate’ the temperature rise. You can ‘measure’ the temperature but not the temperature rise. (b) you need to be sure the reaction has taken place. The reaction may be over and the products cooling down after 10 minutes. (c)is the correct and it also clearly states a thermometer will be used temperature rise = the outcome variable
Example of Pupil Report Which is best? (a)Aim - to find out how the concentration of the acid affects the temperature (b)Aim - to find out how the concentration of the acid affects the temperature rise (c) Aim - to find out what affects the temperature rise.
Example of Pupil Report (b) is the best answer (a) uses temperature rather than temperature rise (b)mentions links both what is being altered (the concentration of the acid) to what is being observed (the temperature rise) (c) does not mention what is being altered.
Example of Pupil Report Method 20 cm 3 2 mol/l sodium hydroxide was added to a small beaker and the temperature noted. 20 cm 3 2 mol/l hydrochloric acid was added to the beaker of alkali.
Example of Pupil Report Method The highest temperature was noted. Which is the correct diagram?
Example of Pupil Report Method The first is a picture showing 3 dimensions. The second is best. It is a 2 dimensional drawing showing a ‘slice through’ the apparatus.
Example of Pupil Report Method The experiment was repeated using 1.5 mol/l hydrochloric acid then 1 mol/l hydrochloric acid. Is this correct?
Example of Pupil Report Method Yes. Only the concentration of the acid is being altered. concentration of acid = input variable
Example of Pupil Report Results Concentration of acid (mol) Temperature before (°C) Temperature after (°C) Temperature rise (°C) 222286 1.521.5264.5 12224.52.5 Is this correct?
Example of Pupil Report Results Concentration of acid (mol)Temperature before (°C)Temperature after(°C)Temperature rise (°C) 222286 1.521.5264.5 12224.52.5 The table has clear rows and columns. The headings are correct. All the raw results (the readings from the thermometer) are given. The temperature rise is correctly calculated each time. The units for concentration should be mol/l not mol.
Example of Pupil Report Results Is this correct?
Example of Pupil Report Results The student chose to change the concentration of the acid (the input variable). This is along the x-axis which is correct. The scale along the x-axis is not even. the distance between 1 and 2 is twice as long as teh distance between 0 and 1. There are no units up the y-axis. It should say °C The first point is plotted at 2.4 instead of 2.5. The crosses used to plot the points should be smaller and drawn with a SHARP pencil.
Example of Pupil Report Conclusion The concentration of the acid does affect the size of the temperature rise. Is this correct?
Example of Pupil Report Conclusion No. The conclusion is too vague. It dos not give a direction. It should be: The higher the concentration of the acid the higher the temperature rise.
Example of Pupil Report Evaluation The thermometer used had 1°C gradations. Using a thermometer with 0.1°C gradations would have allowed the temperatures to be measured more accurately. Only the temperature of the alkali was measured before mixing the. Measuring the temperature of the acid before the experiment too and averaging the starting temperatures would have been more accurate. Repeating the experiment several times and calculating an average for each concentration of acid used would give more reliable results. Some of the heat energy as lost to the surroundings. Insulating the beaker would have reduced the heat lost. Are each of these valid?
Example of Pupil Report Evaluation Yes, all the suggestions are valid.