Assessment in the Diploma Program Assessment is by means of examination and practical for both higher and standard level chemistry courses. Examination weighting - 76%  Practical work weighting - 24% 

IB Chemistry: Lab Report Format Writing good lab reports is very important in IB as they make out a big part of your final grades in the experimental science subjects. The key to writing a good lab report is to find out what is asked for and include all those parts in your report.

IB Chemistry: Lab Report Format Introduction First you should give the aim of the investigation. It should be clear and concise. If the teacher states the aim you should not just copy that down, you need to change it to get a full score.  Second, you do not need to write the hypothesis and prediction of the investigation. But you have to write the research question clearly. If you are writing, the hypothesis needs to be very clear, giving an exact and complete description of what might happen (and why). The prediction is written like: If ……..  You can also give a general background to the study if you feel like it ís relevant and necessary

Independent Variable The independent variable is the one that you alter throughout your experiment. For an example, if you investigate the effect of temperature on yeast fermentation, then the different temperatures that you use are the independent variable.   

Dependent Variable The dependent variable is the variable that you measure. Using the yeast example, the dependent variable would be the amount of CO2 produced by the yeast (this shows how well the fermentation is going).  

Controlled Variables The controlled variables are the ones that you try to keep constant throughout your experiment so that they do not affect your experiment. If investigating the effect of temperature in yeast fermentation, the controlled variables would be the amount of yeast and water, the time for fermentation, etc.

Investigations suitable for design The possible dependent and independent variables are given in the suggestions below so as to aid students to plan and write lab report for the assessment of design. These variables are not to be given to the students when setting the task, however. In order to make an exercise on the dependent and independent variables we are sharing these examples with you.

Investigations with many possible independent variables that are suitable for larger groups

Investigations with many possible independent variables that are suitable for larger groups

IB Chemistry: Lab Report Format Materials and Methods First give a list of all the equipment used in the experiment. Give the size of beakers/measuring cylinders, etc, used, give the names of any chemicals that are used in the experiment. You can use a diagram (picture) to show the experimental set up if you find it necessary. Now you should describe the method. It should be written in past tense (i.e. not written as a guide on how to carry out the experiment again, but rather, how you did it). The steps in the experiment are either self-evident or explained.

IB Chemistry: Lab Report Format Materials and Methods In this part you should explain the different variables. Write how the independent variable was varied. Using the yeast example, the independent variable can be varied by placing the fermentation tubes in hot water baths of different temperatures. Write how changes of the dependent variable were monitored. You should write how you got your results, e.g. by reading from the scale on the fermentation tube to see how much CO2 that has been produced.

IB Chemistry: Lab Report Format Materials and Methods Write how the controlled variables were controlled. Using the yeast example, you write that you made sure that the amount of yeast used in each fermentation tube was the same (because you used a scale), that you used a watch to make sure that the time that the tubes were allowed to ferment was the same for all tubes. Write how you made sure that the sufficient relevant data was recorded. Describe the method for data collection, i.e. if you had several trials, if you used controls, methods of measurements, if your calculations are correct, etc.

IB Chemistry: Lab Report Format Data collection/quantitative data Record all your raw data in tables. The tables should be numbered and named. Tables should have captions in which you briefly describe the contents of the tables and how you recorded the results. Titles, labels (trial 1, trial 2, etc.) should be used. units and the uncertainties should be given in the captions of the tables. Uncertainties should be consistent throughout the data. Use “dots” to show decimal points, NOT “commas!”

Data collection/qualitative data While Record all your qualitative data (collected by using your 5 senses) use past tenses. Be specific! Make it comprehensible. Use a paragraph style. E.g. Color of solutions, color of solid crystals, size of crystals, lustre/ appearance of crystals, was the process exothermic/ endothermic?observation of any gas release or bubbles during the rxn, any color change or sound during the rxn, any smell?(Note:you’re not allowed to smell any chemicals!)

IB Chemistry: Lab Report Format Data Processing and presentation The data should be processed (calculated) correctly and clearly by using 3 step problem solving method) Label the calculations for each trial present in tables (as above) and graphs.  If you use graphs, they should have a caption in which you describe the contents of the graph. The axes of the graphs have to be labelled with units and uncertainties. the points have to be plotted correctly and best-fitting line/curve has to be used. Make sure that you use the correct type of graphs. If both variables are continuous, use a point graph.  State the sources of the values of constants like Cwater, R, etc.  

Data Processing and presentation Present the results of your calculations in a table with appropriate uncertainties. Do the error propagation (calculation of uncertainties for the results of the calculations and calculation of % error) Units and significant figures have to be kep track of throughout the calculations Use dots to show the place of the decimal point

IB Chemistry: Lab Report Format Conclusion Write a conclusion based on an interpretation of the gathered results and relate your conclusion to the research question, purpose, or hypothesis. State theoretical values of your results with its sources. Compare your results with each other, and with the literature value.

Conclusion State % error Compare % error with the mean value of the % uncertainties

IB Chemistry: Lab Report Format Evaluation/Discussion Are the results accurate?Explain. Are the results precise? Explain.(are all the results within the limits of +/- uncertainty values of the mean value?) Why do you have a big value of % error? (If % uncertainty of the mean value is smaller than % error, the % error is big)

Evaluation/Discussion Explain the possible reasons for this big % error in terms of: Measurement techniques (hint: if your results aren’t precise, that means you have poor measurement techniques. You should have more trials if you have imprecise results) Random errors( due to uncertainties of the equipments. You should use more precise equipments and have more trials to reduce this) “systematic” errors (hint: if results aren’t accurate,that means you have sys errors.These are due to the apparatus that wasn’t good enough and used in the experiment , any flaw in the procedure like not collecting the data to draw a graph to determine the value of ΔH, etc.). You have to indicate the direction effect of the sys errors on the results, if possible. “assumptions” of the experiment. Were there any assumptions affecting the results in the experiment? Could you control the controlled variables during the experiment? Evaluation/Discussion

Evaluation/Discussion Write about the source of error, but do not include personal mistakes. Do NOT say human error!!!

Evaluation/Discussion Suggest realistic improvements (that can be carried out in the school lab) to reduce/eliminate the errors and explain how these improvements will reduce/ eliminate the errors Improve the control of the variables. Any flaw in the procedure !!!Suggestions should be specific, not vague. Discuss further investigations that are of interest and  can be carried out and new questions that could be posed.

Interpreting the relevant assessment criteria Data collection and processing: Aspect 1 (recording raw data) Table 1: DCP aspect 1 = “partial” Final volume / cm3 42.5 41.5 Initial volume / cm3 2.5 1 Volume of base required / cm3 40.0 40.5 Colour of solution at end point light pink dark pink

Some appropriate raw data is recorded but there are no uncertainties and the number of decimal places is inconsistent. Either of these factors reduces the level of achievement for aspect 1 of data collection and processing to partial/1.

Table 2: DCP aspect 1 = “partial” Run 1 Run 2 Run 3 Initial volume / cm3(±0.1 cm3) 0.0 2.7 1.0 Final volume / cm3(±0.1 cm3) 42.2 42.7 41.5 Volume of base required / cm3(±0.2 cm3) 40.0 40.5 Some appropriate raw data is recorded with units and uncertainties. However, relevant qualitative observations were not recorded and the level of achievement for aspect 1 of data collection and processing is partial/1.

Table 3: DCP aspect 1 = “complete”   Trial 1 Trial 2 Trial 3 Initial volume / cm3 (±0.05 cm3) 1.00 2.55 0.00 Final volume / cm3 (±0.05 cm3) 42.50 43.25 40.50 Total volume of base required / cm3 (±0.1 cm3) 41.5 40.7 40.5 Colours of solutions: acid, base and phenolphthalein indicator were all colourless. At the end point, the rough trial was dark pink. The other two trials were only slightly pink at the end point. The student records appropriate qualitative and quantitative raw data, including units and uncertainties. The level of achievement for aspect 1 of data collection and processing is complete/2.

Data collection and processing: Aspect 3 (presenting processed data) Figures 1 and 2: DCP aspect 3 = “complete”

Figure 1 is a graph of the gas law data showing the significant uncertainty. The computer drew the uncertainty bars based on the student entering the correct information, which in this case was 0.5 mm for each value. Figure 2 does not show the uncertainty bars. In chemistry, students are not expected to construct uncertainty bars. In both graphs the title is given (although it should be more explicit), and the student has labelled the axes and included units. The level of achievement for aspect 3 of data collection and processing for both graphs is complete/2.

Figure 3: DCP aspect 3 = “partial” In figure 3, the student does not include a title for the graph, and the units are missing. The level of achievement for aspect 3 of data collection and processing is partial/1.

Figure 4: DCP aspect 3 = “not at all” In the examples shown in figure 4, the first student has failed to draw a best-fit line graph and the second has drawn no line at all. The units and the titles of the graphs are missing. In the second graph, poor use is made of the x-axis scale/ The level of achievement for aspect 3 of data collection and processing for both graphs is not at all/0.

Conclusion and evaluation: Aspects 1, 2 and 3 (concluding, evaluating procedure and improving the investigation) When attempting to measure an already known and accepted value of a physical quantity, such as the charge of an electron, the melting point of a substance, or the value of the ideal gas constant, students can make two types of comments:

The error in the measurement can be expressed by comparing the experimental value with the textbook or literature value. The experimental results fail to meet the accepted value (a more relevant comment).

Figure 5: CE aspect 1 = “partial”, aspect 2 = “not at all”

Conclusion and evaluation: Intermolecular bonds are being broken and formed which consumes energy. There is a definite correlation between the melting point and the freezing point of a substance. If good data is collected, the melting point should be the same as the freezing point. A substance should melt, go from solid to liquid, at the same temperature that it freezes, goes from liquid to solid. Our experiment proved this is true because, while freezing, the freezing point was found to be 55 °C, and when melting, the melting point was also found to be 55 °C (see graph). states a conclusion that has some validity. No comparison is made wThe student ith the literature value. There is no evaluation of the procedure and results. The level of achievement for aspect 1 of conclusion and evaluation is partial/1. The level of achievement for aspect 2 is not at all/0.

Figure 6: CE aspects 1, 2 and 3 = “complete”

Melting point = freezing point = 55.0 ± 0.5 °C Conclusion and evaluation: Literature value of melting point of para-dichlorobenzene = 53.1° C (Handbook of Chemistry and Physics). The fact that % difference > % uncertainty means random errors alone cannot explain the difference and some systematic error(s) must be present. Melting point (or freezing point) is the temperature at which the solid and the liquid are in equilibrium with each other: (s) ⇌ (l). This is the temperature at which there is no change in kinetic energy (no change in temperature), but a change in potential energy. The value suggests a small degree of systematic error in comparison with the literature value as random errors alone are unable to explain the percentage difference.