diwali
- 1. GENERALISED PRAC REPORT FEEDBACK Introduction: Many people didn’t provide much detail in the introduction. This section is designed to introduce the reader to your paper, and make sure that they are aware of the different aspects of the content so that they can follow along easily and understand what you are saying and doing. After the introduction, there should be no new concepts added, because the reader has not yet been introduced it. As a guide, you should write down the main points that are in the report (in this case, Spectrophotometry, absorbance, standard curve, and Beer-Lambert’s law), and then for each of those, define what its, how it works, why it is used, and any pros or cons. There are more than 2 ways to determine concentration of a substance, but we only looked at the standard curve method, and the Beer-Lambert law calculation The introduction should be concise, and not be repetitive Check to make sure that your writing flows well and makes sense. Don’t have ambiguous phrases that make your meaning unclear. Aims: The way this was done seemed to have the class split. The aims need to be one or two sentences at the end of the introduction which clearly identify what the focus of the project is. It needs to be in past tense, because you have done it and you are telling people what you have DONE, and it needs to be considered in all the other sections of the paper. Each section should reflect how you did your experiments and discussion to achieve the aim of the paper. The aim of this paper was to use DCIP in colorimetric spectrophotometry to compare and contrast two concentration detection methods; the standard curve method, and the Beer-Lambert method. If your aim is clear on the paper and in your mind, there is much more focus in the report and it is easier to determine what should be discussed and what shouldn’t. Methodology: Most people referenced the lab book, but quite a few people chose to write out the methods instead. As a word of caution, you are more likely to get something wrong if you do the unnecessary work. If you choose to write the methods, they should be… A maximum of half a page in length In paragraph form In your own words; and Clear and concise.
- 2. Results: Writing up the results is the easy part. You put in the tables and figures that are required to meet your aims, and include calculation that you used to get final results. You ALSO need to provide a brief description of your results. DO NOT start discussing or interpreting your results here. That is saved for the discussion. An example is… The standards used for the standard curve showed that the reliable linear range of detection was 0.000-0.789 (Fig.1, Table 1). All unknowns fell within this range, and therefore did not require further dilution. The unknown concentrations of DCIP were calculated in μmol/L with both the standard curve method (A=21.5 μmol/L, etc.) and the Beer-Lambert law method (A=15.0 μmol/L, etc.), and the summary and comparison of these results are shown in table 2. For each unknown, there was a consistent difference between methods, where the standard curve had a tendency to underestimate values when compared to the Beer-Lambert law method (A=6.5 μmol/L difference, etc.). Notice that there are no reasons given for what has been observed. From this, you don’t NEED to look at the tables unless you really want to look at the detailed data and calculations. I know that they trust their standard curve, and that the results can now easily be transferred into the discussion by talking about them in the same layout. Remember: Absorbance is ALWAYS reported as 3 decimal places (i.e. 0.320, 0.712, >2.000; not 0.32, 0.7115, >2). Use a line of best fit with your graphs to read your unknowns off Include as much information on your graph as sensibly possible (i.e., units, wave length, legends etc.) Make your calculations clear so that if you are doing something wrong, then they can be corrected NOW. Include table and figure legends. Table legends go ABOVE the table, figure legends go BELOW the figure. If you have included a table or figure, make sure you refer to it in the results paragraph and in the discussion section. When doing your graph in excel, use a scatter plot. This will make your axis to scale. You can then write click on the data points and add a R2 value and an equation to calculate the actual results of your unknowns directly from the graph. Discussion: This is the part where you show your knowledge in the area, and whether or not you understand the purpose and the concepts of the assignment. You need to begin by seeing if your initial results are valid. If they are not, give all realistic possible reasons for their invalidity, if they are, state what evidence you have (i.e. there is a strong linear correlation in the standard curve, and all the results fall within the linear range). The look at your results and think about what they mean. Do they make sense? Do they do what you expected them to? What does it mean? Think about why they might not
- 3. be what you expected, and offer causes of error or variation, whether it is due to the methodology, the environment, or if it makes sense, but wasn’t what you had expected. When comparing two methods, look at the pros and cons of each with a solid argument so that you can write a convincing conclusion at the end of the paper. More specific comments/corrections on submitted discussion points: A blank references the machine to zero. If you put a coloured solution into the machine and blank it, you will also get zero. Just because the machine reads zero, does not mean that no light is being absorbed. This simply means that the machine now knows what a solution with no chromophore (molecules that give the colour which we are measuring to the solution) looks like. If you are measuring the content of a red chromophore in a yellow solution, you would blank the machine to the untreated yellow solution. Light is still being absorbed, but the machine now knows that in this circumstance, any red light is not from the chromophore we want to detect (if this is confusing, ignore this. You will learn it at a later time). Consider the limitations of each method before determining your “preferred” method. Beer- Lambert’s law does not consider what you have blanked your solution against, nor does it account for variation of the laboratory environment or the person doing the test, where as the standard curve method does. On the other hand the standard curve requires more technical work to achieve the result, and is only correct if the standards are the actual concentration that they are thought to be. Conclusion: This just needs to be a sentence or so stating what you found from your report, and what it means. Make sure that this is clear and a separate paragraph, or even under a heading. Example: It was found that the standard curve method is more appropriate for use than the Beer-Lambert law method because the standard curve method allows for laboratory variation, and systematic error, and provides a reliability range, whereas Beer-Lambert’s law excludes these considerations. Overall comment: Make sure you plan out your report before you write it. Put dot points under each section so that you know you have covered everything that you set out to, and get your head into gear before writing your report. Make sure your aim is clear so that you can target the correct information and focus your writing in the right direction. The most common error in this report was derived from the aim. People did not get the aim right, and therefore wrote the report to their own aim which resulted in information being missed that could have easily been included, had the aim been correct.