Crime scene investigators keep a wide variety of compounds on hand to with identifying unknown substances they find in the course of their duties. one such investigator, while reorganizing their shelves, has mixed up several small vials and is unsure about the identity of a certain powder. elemental analysis of the compound reveals that it is 63.57% carbon, 6.000% hydrogen, 9.267% nitrogen, 21.17% oxygen by mass. which of the following compounds could the powder be?

The question is incomplete, here is the complete question:

Crime scene investigators keep a wide variety of compounds on hand to help with identifying unknown substances they find in the course of their duties.  One such investigator, while reorganizing their shelves, has mixed up several small vials and is unsure about the identity of a certain powder.  Elemental analysis of the compound reveals that it is 63.57% carbon, 6.000% hydrogen, 9.267% nitrogen, 21.17% oxygen by mass. Which of the following compounds could the powder be?  

a.) = 3,4-methylenedioxymethamphetamine (MDMA), illicit drug

b.) = hexamethylene triperoxide diamine (HMTD), commonly used explosive

c.) = heroin, illicit drug

d.) = acetaminophen, analgesic

e.) = 2,4,6-trinitrotoluene (TNT), common used explosive

f.) = morphine, analgesic

g.) = methamphetamine, stimulant

h.) = caffeine, stimulant

The powder could be acetaminophen, analgesic  having chemical formula

Explanation:

We are given:

Percentage of C = 63.57 %

Percentage of H = 6.000 %

Percentage of N = 9.267 %

Percentage of O = 21.17 %

Let the mass of compound be 100 g. So, percentages given are taken as mass.

Mass of C = 63.57 g

Mass of H = 6.000 g

Mass of N = 9.267 g

Mass of O = 21.17 g

To formulate the empirical formula, we need to follow some steps:

Moles of Carbon =

Moles of Hydrogen =

Moles of Nitrogen =

Moles of Oxygen =

For the mole ratio, we divide each value of the moles by the smallest number of moles calculated which is 0.662 moles.

For Carbon =

For Hydrogen =

For Nitrogen =

For Oxygen =

The ratio of C : H : N : O = 8 : 9 : 1 : 2

The empirical formula for the given compound is

Hence, the powder could be acetaminophen, analgesic  having chemical formula

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.