MEASUREMENTS IN BIOLOGY: MAKING SOLUTIONS, AND DILUTIONS (30 points)
Name:_______John Gibson____________________________
Section # (801-819):______807A_________________
Instructor/TA:_______George Gikas______________________
Describe in words how you would prepare the following solutions, be specific as to what measurement instruments you would use at each step and show all your work, calculations, and any necessary conversions:
(2 pts) How would you prepare 200 mLs of a 12% sucrose solution (weight/volume)
Calculate the weight of sucrose. W = C * V , C = 12/100 g/mL , V = 200 mL.
W = 200 mL * 12/100 g/mL = 24 g
Weigh out 24 grams of sucrose with the scale tared with a weighing boat.
Fill a graduated cylinder with dH2O to 150 mL (3/4 of the target volume 200 mL). Match the mark to the lowest point of the meniscus.
Pour the distilled water into a beaker, add the sucrose, and stir until sugar is dissolved.
Pour the solution back into the graduated cylinder, then add more dH2O into the cylinder until the volume reaches 200 mL
(2 pts) How would you prepare 1.5 liters of 2 M KCl (MW=74.55 g/mol)
Calculate the weight of KCl. W = MW * M * V, MW = 74.55 g/mol, M = 2 mol/L, V = 1.5 L
W = 74.55 g/mol * 2 mol/L * 1.5 L = 223.65 g
Weigh out 223.65 grams of KCl with the scale tared with a weighing boat.
Fill a large graduated cylinder with dH2O to 1.125 L (3/4 of the target volume 1.5 L). Match the mark to the lowest point of the meniscus.
If the largest graduated cylinder in the lab is 1 L, fill it to 1 L, pour water into a large beaker, then fill the cylinder to 0.125 L and pour water into a breaker.
Pour the distilled water into a beaker, add the KCl, and stir until salt is dissolved.
Pour the solution back into the large graduated cylinder, add more dH2O from a beaker to reach 1.498 L, then use a transfer pipet to add more water slowly until it reaches precisely 1.5 L.
(2 pts) From the 2 M stock above, how would you prepare 500 mL of 0.25 M KCl
V1 * M1 = V2 * M2
M1 is 2 mol/L
V2 is target 500 mL = 0.5 L
M2 is target 0.25 mol/L
V1 * 2 mol/L = 0.5 L * 0.25 mol/L
V1 = 0.5 L * 0.25 mol/L / ( 2 mol/L ) = (0.5 * 0.25 / 2) L = 0.0625 L = 62.5 mL
So, pour 62.5 mL of the stock into a graduated cylinder and use a transfer pipet to transfer the small volumes at the 60 mL mark to reach the exact 62.5 mL mark, matching the mark to the lowest point of the meniscus. Then, add dH2O from a beaker until the volume’s lowest meniscus point reaches the 498 mL mark. Then use a transfer pipet to add more distilled water slowly to reach exactly 500 mL, matching the mark to the lowest point of the meniscus.
(2 pts) Prepare 20 mLs of a 1:4 dilution of a stock solution directly. How much stock solution? How much water?
V1 * M1 = V2 * M2
M2 = 1/4 * M2
V2 = 20 mL
V1 * M1 = 20 mL * 1/4 M1
Cancel out M1 on both sides
V1 = 20 mL * 1/4 = 5 mL
V2 - V1 = 20 mL - 5 mL = 15 mL
So, pour 5 mL of the stock solution into a graduated cylinder using a transfer pipet, , matching the mark to the lowest point of the meniscus. Then add distilled water with a serological or transfer pipet slowly to reach 20 mL, matching the mark to the lowest point of the meniscus.
(1.5 pts) Mark each of the following serological pipets at the 2 mL marking:
(2.5 pts) When is it appropriate to use each of the following and why.
Graduated cylinder
When the needed volume is between 1 mL and 1000 mL (or the lab’s largest graduated cylinder’s volume) and the required precision is about 2 significant figures.
Micropipet
When the needed volume is between 0.1 μL and 1000 μL (1 mL) .
Serological pipet
When the needed volume is between 1 mL and 25 mL (or the lab’s largest serological pipet’s volume) and the required precision is 0.05 mL to 0.1 mL
Beaker
When a precise volume is not required
Transfer pipet
When a precise volume is not required
Convert the following (show all work and conversion factors):
(2 pts) 25 mM to M
25 mM * (1 M / 1000 mM) = 0.025 M
Answer: 0.025 M
(2 pts) 356 g to µg
356 g * (1,000,000 µg / 1 g) = 356,000,000 µg
Answer: 356,000,000 µg
(2 pts) 0.250 mL to µL
0.250 mL * (1000 µL / 1 mL) = 250 µL
Answer: 250 µL
(2 pts) 600 µM to M
600 µM * (1 M / 1,000,000 µM) = 0.0006 M
Answer: 0.0006 M
(2 pts) Complete a 1:5 dilution series with each tube containing a final volume of 10 mL. Indicate the dilution factor of each tube relative to the stock and the volume of water and solution in each tube. The first tube represents the concentrated stock solution, make dilutions in the 4 remaining tubes.
Answer: Procedure: First fill each of the empty 4 tubes with 8 mL of dH2O. Then, draw from the leftmost tube 2 mL of solution with a serological pipet to the next tube, shake/mix the tube, and repeat it a total of 4 times toward the right until the 5th tube.
Dilution factors: Relative to the original tube, the first new tube is 1:5 diluted, then 1:25, then 1:125, then 1:625 in the last tube.
(4 pts) From the data below create a line graph with an individual line for both the skier and the snowboarder. Be sure to connect your data points and write an explanation on how you created the graph. Think of your explanation as notes/instructions to yourself that you can refer to later in the semester.
Open google sheet, enter the data including the first row of colume meaning. Then select all the data cells with cursor and click Insert->Chart. Double-click on the title to change it to be more descriptive. Double-click on the vertical axis to open up the editing of the vertical title and add the variable name with its unit. Double-click on the horizontal axis to change the grid to 10 seconds per grid.
(4 pts) Using the same data create a bar graph showing the average speed of each thrill seeker. The x-axis should have the sport and the speed on the y-axis. Write an explanation on how to calculate the average using excel and create the graph.
Add a new row under the existing data cells. Enter data with formula “=AVERAGE(:)” to automatically calculate the average velocity of each column. Insert yet another row between the new average row and the data cells above. Add the sport name to the new row aligned with original column sport name. Select the 2 new rows with the cursor, then click Insert->Chart.
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