Map EA Sapling Learning macmillan laarnino You want to prepare a solution with a

Question

Map EA Sapling Learning macmillan laarnino You want to prepare a solution with a concentration of 200.0 AM from a stock solution with a concentration of 500.0 mM. At your disposal you have 5- and 10-mL transfer pipets and volumetric fasks of sizes 100, 250, 500, and 1000 mL. Which of the following serial dilutions will give you the 200.0 uM solution? Produces a 200.0 UM solution Does not produce a 200.0 pM solution Dilute 10.00 mL of the stock solution Dilute 10.00 mL of the stock solution up to 250.0 mL. Then dilute 10.000 mL of up to 250.0 mL. Then dilute 5.00 mL of the resulting solution up to 1000.0 mL the resulting solution up to 500.0 mL Dilute 10.00 mL of the stock solution Dilute 5.00 mL of the stock solution up to 100.0 mL. Then dilute 10.00 mL of up to 100.0 mL. Then dilute 5.00 mL of the resulting solution up to 1000.0 mL the resulting solution up to 1000.0 mL Dilute 10.00 mL of the stock solution up to 500.0 mL. Then dilute 5.00 mL of the resulting solution up to 250.0 mL.

Explanation / Answer

M = 200 microM

M = 500 milliM stock

V = 5 mL and 10 mL pipets

V = 100, 250,500,1000 mL

apply:

Vstock*Mstock = Vfinal*Cfinal

Vstock*(500*10^-3) = Vfinal*(200*10^-6)

Vstock((500*10^-3)/(200*10^-6)) = Vfinal

Vstock*2500 = Vfinal

that is, if the final volume is 2500 times larger than Vstock, we will have a correct dilution

a)

initially:

ratio

250/10 = 25

25*(1000/10) = 2500; correct ratio!

b)

diluting 5 mL of stock up to 100

100/5 = 20

then..

10 to 1000 = WILL NOT WORK

c)

10 mL of stock up to 500 mL

500/10 = 50

then

50*250/5 = 2500

ratio is kept! this will work

d)

250/10 = 25

then

5/25*500 = 100 ratio is not kept

e)

100/10 = 10

then

5/10*1000 = 500 ratio is not kept

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