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BISC110/S13: Series 1 Lab 1 Boot Camp: Difference between revisions
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BISC110/S13: Series 1 Lab 1 Boot Camp (view source)
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(New page: {{Template:BISC110/S13}} <div style="padding: 10px; width: 725px; border: 5px solid #00cc66;"> <BR> =='''Objectives: In this lab you will learn:'''== #Metric measurements and conversions...) |
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#Transfer the solution into an empty 100mL graduated cylinder and bring the volume to exactly 50mL with deionized water. | #Transfer the solution into an empty 100mL graduated cylinder and bring the volume to exactly 50mL with deionized water. | ||
#Transfer the solution to an empty storage bottle. Label the bottle with the name and concentration of the solution, your initials, your lab section and date.<br> | #Transfer the solution to an empty storage bottle. Label the bottle with the name and concentration of the solution, your initials, your lab section and date.<br> | ||
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=='''PART IV: Dilutions'''== | |||
A helpful animation of [http://www.wellesley.edu/Biology/Concepts/Html/dilutions.html dilution making].<br> | |||
Many solutions will be provided to you this semester as stock solutions. A stock solution is a solution that has been prepared with a greater concentration of solute than is needed for a procedure, so it must be diluted to the proper concentration(s) before use. Consequently, it is very important that you master the concepts and techniques of preparing dilutions early in the semester. A dilution is made by taking an aliquot (a measured portion) of a stock solution, and adding to it an aliquot of a solvent (water or a buffer). This creates a new solution with a lower concentration of solute than was contained in the stock solution. Since the solute concentration of the stock solution is known as well as the volumes of stock and solvent, it is possible to calculate the concentration of solute in the dilute solution. The dilute solution is always less concentrated than the stock or starting solution. There are several ways to describe and prepare dilutions. Explanations are provided in this section as well as a laboratory exercise to introduce you to dilution preparation. | |||
'''A. VOLUME-TO-VOLUME DILUTIONS''' | |||
'''1. Ratio Method''' | |||
This type of dilution describes the ratio of the solute to the total volume of the dilute solution. For example, to make a 1:10 dilution of a 1M NaCl solution, you would mix one part of the 1M solution with 9 parts of solvent (probably water), for a total of ten parts. If you needed 10mL of the 1:10 dilution, then you would mix 1mL of the 1M NaCl with 9mL of water yielding a total volume of 10mL. If you needed 100mL of the 1:10 dilution, then you would mix 10mL of the 1M NaCl with 90mL of water yielding a total volume of 100mL. The new concentration of NaCl in both solutions is determined by multiplying the stock concentration by the dilution ratio: | |||
1M NaCl x 1/10 = 0.1M NaCl | |||
'''2. Direct Calculation Method''' | |||
Sometimes it is necessary to use an aliquot of one solution to make a specific volume of a more dilute solution. To calculate the volume of the more concentrated solution that will be needed to prepare the new solution, you can use the formula: | |||
V1 x C1 = V2 x C2 <br> | |||
V1= volume of more concentrated solution needed to make the new solution (usually the unknown) <br> | |||
C1= concentration of starting solution <br> | |||
V2= final volume of new solution <br> | |||
C2= final concentration of new solution (must be less than C1) <br> | |||
For example, if you have 2.5 ml of a 1M solution of NaCl and you want to make 3 ml of a 0.33M solution of NaCl, you can use the formula to calculate how much of the 1M solution you will need. | |||
V1 x C1 = V2 x C2 <br> | |||
(V1)(1M) = (3mL)(0.33M) <br> | |||
V1 = (3mL) (0.33M)/1M <br> | |||
V1 = 1mL <br> | |||
The calculations show that you will need to use 1mL of the 1M solution. Since the diluted solution is to have a final volume of 3mL, you can calculate the volume of solvent by subtracting V1 from V2 : 3mL – 1mL = 2mL. Therefore, adding 2mL of solvent to 1 ml of a 1M solution of NaCl will yield 3mL of a 0.33M NaCl solution. | |||
'''3. Serial Dilutions''' | |||
Serial dilutions involve the preparation of successive dilutions that vary the concentration of the solute by a constant factor, so that each successive dilution is a multiple of the previous dilution. For example, in ten-fold serial dilutions each successive dilution is one tenth of the previous dilution yielding dilution ratios of 1/10, 1/100, 1/1000, and so on. Serial dilutions may be used to prepare a series of standard concentrations for a biochemical assay, or to dilute a very dense culture of microorganisms to a concentration suitable for counting. It is very important to prepare serial dilutions carefully since each successive dilution will magnify the effect of any previous error. | |||
How would you prepare a dilution series? As shown in Figure 1, you could begin with a stock solution of 1 mg/ml and set up a series of dilutions in which the dilution ratio relative to the stock solution progressively changes by one-half. In this instance, the concentrations of the successively diluted solutions would be 1/2, 1/4, 1/8, and 1/16 of the original concentration. If you needed 1 ml of each dilution, you could set up a series of 5 test tubes, with the first one empty and the rest with 1mL of solvent. You would then pipette 2mL (twice the volume needed for your test) into tube 1. Then transfer 1mL of that volume to tube 2, making a 1/2 dilution since there was 1mL of water in tube 2. After mixing the contents of tube 2, half that sample (1mL) would be transferred to tube 3, making a 1/4 dilution since the 1 ml of water that was already in tube 3 will dilute the incoming 1/2 dilution by 1/2 (1/2 x 1/2 = 1/4). This procedure is repeated until the last tube is reached, which will contain 2 ml of a 1/16 dilution of the stock solution. | |||
[[Image:BISC110.1.10.jpg]] | |||
'''B. Prepare Serial Dilutions of Cobalt Chloride and Cupric Chloride Stock Solutions''' | |||
<br> | |||
Each pair will use the stock solution you just prepared to create a series of 4 dilutions. Each dilution in the series will differ from the previous dilution by 1/2, so the dilution ratio for each tube is 1/2, 1/4, 1/8 and 1/16. Calculate the concentrations of cupric chloride or cobalt chloride that the tubes will contain after the dilutions have been prepared, and record them in your lab notebook. | |||
#Label four microcentrifuge tubes with the dilution ratios: 1/2, 1/4, 1/8 and 1/16. | |||
#With a 200 μL micropipette and clean tip add 100 μL deionized water to each tube. Discard the tip as instructed by your instructor. | |||
#Using a clean pipette tip, add 100 μL of stock solution to the tube labeled 1/2, close the lid, and mix by inversion (not vortexing). | |||
#Use a clean pipette tip to add 100 μL of the 1/2 dilution to the tube labeled 1/4; mix. | |||
#Use a clean pipette tip to add 100 μL of 1/4 dilution to the tube labeled 1/8; mix. | |||
#Use a clean pipette tip to add 100 μL of 1/8 dilution to the tube labeled 1/16; mix. | |||
#Using a clean pipette tip, remove 100 μL of solution from the 1/16 tube, and discard it in the sink. You now have four tubes containing 100 μL of four different working concentrations of your reagent. Observe the color intensity of the four solutions and record in your lab notebook. Also, observe the relative volumes of the four solutions. If they are different from each other, then inaccurate pipetting has occurred. Save these dilutions for use next week.<BR> | |||
