Techniques among pipette users vary with background, personal preferences, and training. For example, a ten-fold serial dilution could result in the following concentrations: 1 M, 0.1 M, 0.01 M, 0.001 M, and. Typically, the dilution factor remains constant for each dilution, resulting in an exponential decrease in concentration. Serial dilutions involve diluting a stock or standard solution multiple times in a row.Varying the color of the filters and the path length will aid in seeing lower concentrations.The ability to make dilutions is essential to working in biology, chemistry, cooking and many other fields. Repeated "serial" dilutions will be necessary to determine accurate concentration readings.3. Students are given an unknown dye solution and asked to determine its concentration by comparing it with standards they create.For example, an adjustable pipette will be much better at measuring out a few millilitres of a solution when performing a serial dilution than using a 50 mL.2. At the conclusion of this. Rationale: This experiment seeks to introduce one to the technique and method of serial dilution by first guiding one through the process of serial dilution involving dye and then instructing one in the technique of serial dilution of Tetrahymena solution.
The students will have a much wider color intensity range to work with, due to the highly concentrated nature of the dyes.Students may not see the relevancy of using a dye, but a dye in this experiment could represent an environmentally toxic poison. In this lesson we will use household food coloring. In this experiment the students use the tools they learned to solve a slightly more difficult problem. Life does not always hand you all of the tools to solve problems in a "cookbook" manner. (A sheet of translucent white plastic over a sunlit window works great!)Use the spectrophotometers from the SIMPLE DILUTION lesson, students working in groups of 4-5 a light table, students working in groups of 2. (Larger size bottles should be purchased for refills for future classes.) one small package of assorted food colors for each lab group. As a teacher you could invent a scenario of "pretending" it is the toxin. graduated cylinders (10ml) and eye droppers Too high a concentration and the students may think they have solved the problem too easily. set of unknowns made up ahead of time, dilute but still showing visible color. set of 10 clean test tubes of the same size & test tube rack Make sure they have several colors, so they are forced to make a choice. They can all get A's or all get F's This is not a competition. They may talk among themselves and with other groups. Serial dilutions will need to follow. Suggest that their first dilution might be 1-2 drops in 10 ml. Hand out materials and one unknown per groupA) They are to determine the concentration of the unknown to the highest accuracy possible (Assume that the dye in the food color bottles is 100%.)B) Their grade depends on the accuracy of their answer, their reasoning, and conservation of resources. DON'T GIVE IN! They have all the tools they need. cooperate in a group in determining strategies, assigning duties, responsibilities and doing the workSome students will find this experiment frustrating, because there is no specific procedure given. use their records to calculate the concentration of their unknown how many serial and linear dilutions (quite a few, as the dyes are VERY concentrated) Do not hand out any more dye or materials during the experiment. Looking at the color choices of dye, they select the red dye as being the closest to the color of the unknown. Green seems to work the best. Placing the unknown and a blank (zero dye concentration, same water as used later to make dilutions) against the light table they try the three colored filters to see which gives the highest contrast between the two. The group is handed an unknown that has a "pink" color. Pdf to work converter for mac1 drop = 0.05ml so 2 drops = 0.1 ml. They decide that the two drop solution can be used as a starting point to make further dilutions. (They try one drop also, but this is still too intense) The resultant solution is more intense than the unknown. As an experiment, two drops are added to 10ml of water and mixed. Serial Dilution Lab Conclusion Series To MakeThe differences are so subtle at this point they decide not to try further refinements in their dilution series. It appears that the dye is somewhere between 0.04% and 0.08%. NOTE: they could have chosen a different dilution series to make the numbers easier to deal with, such as 0.2%, 0.15%, 0.10% 0.05%, & 0. 0.2% is selected as the "new stock" and is diluted using the simple dilution method to the calculated values of: 0.2%, 0.16%, 0.12%, 0.08%, 0.04% & 0. How did you choose the dilutions that you used? Could you have used a different series? The major math concept introduced in this lesson is repeated multiplication of percentages and/or fractions (depending on how students decide to follow the dilutions). (Each student might be required to turn in a separate lab report, but they are allowed to discuss possible layouts and what should be included.)As you can see from the above scenario, careful record keeping and math are very important to successful completion of this lab. Each student presents their part of the process and discusses the problems and solutions. They spend the rest of the period laying out their lab reports together. They clean up their lab space and return the materials to the appropriate locations. Did the group follow logical steps to arrive at a solution? What causes this? How could you make use of this fact?In this lab it is VERY important to assess the thinking that went on as well as getting to the answer: Notice the intensity of the color. Look down the end of the tube, from top to bottom. How dilute a solution is it possible to mix and still detect above the blank? With and without the colored filter? Did everyone in the group understand what was done and why? (Individual lab notes and reports should tell you this. Did any group come up with a unique way of solving the problem that went beyond prior learning?
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