Question

For your research project, your group is planning to treat embryos with acetaminophen at a concentration of 50 ug/L plus varying concentrations of dextromethorphan between O and 100 uM. You have stock solutions of 500 ug/L acetaminophen and 1 mM dextromethorphan to work with. If you wanted to treat some embryos with final concentrations of 50 ug/L acetaminophen and 20 uM dextromethorphan in a total volume of 10 ml, how would you make up 9 ml of solution containing both acetaminophen and dextromethorphan, to which you could add 1 ml of embryo water containing the embryos? A. Add 0.5ml of 500 ug/1 acetaminophen and 0.5 ml of 1 mM dextromethorphan to 8 ml of water B. Add 1 ml of 500 ug/l acetaminophen and 0.2 ml of 1 mM dextromethorphan to 8.8 ml of water. C. Add 0.1 ml of 500 ug/l acetaminophen and 0.5 ml of 1 mM dextromethorphan to 8.4 ml of water. D. Add 1 ml of 500 ug/I acetaminophen and 0.2 ml of 1 mM dextromethorphan to 7.8 ml of water. E. Add 1 ml of 500 ug/I acetaminophen and 2 ml of 1 mM dextromethorphan to 6 ml of water.

Answer 1

Answer:

D

Explanation:

When a dilution is made, a volume of the stock solution is collected and then is mixed to the solvent. The total amount of the solute (number of moles or mass), must be equal in the volume of the sample and at the final volume, because of the Lavoiser's law (the matter can't be created nor destructed).

The mass or the number of moles is the concentration (C) multiplied by the volume (V), so, if 1 is the sample of the stock solution, and 2 the diluted solution:

C1*V1 = C2*V2

The final volume of the solution is 10 mL. So, let's identify the volume needed for each stock solution.

Acetaminophen

C1 = 500 ug/L

C2 = 50 ug/L

500*V1 = 50*10

V1 = 1 mL

Dextromethorphan

C1 = 1 mM = 1000 uM

C2 = 20 uM

1000*V1 = 20*10

V1 = 0.2 mL

So, the volume of water needed is the total less the volume of the stocks solutions less the volume of the embryo water:

V = 10 - 1 - 1 - 0.2 = 7.8 mL

Thus, to to the solution, it's necessary to add at 1 mL of the embryo water 1 ml of 500 ug/I acetaminophen and 0.2 ml of 1 mM dextromethorphan, and 7.8 ml of water.