At a certain temperature the vapor pressure of pure heptane (C_7 H_16) is measured to be 170. torr. Suppose a solution is prepared by mixing 86.7 g of heptane and 125. g of acetyl bromide (CH_3 COBr). Calculate the partial pressure of heptane vapor above this solution. Round your answer to 3 significant digits. Note for advanced students: you may assume the solution is ideal.

Explanation:

The given data is as follows.

       Pressure (P) = 170 torr,      mass of heptane (m) = 86.7 g

First, we will calculate the number of moles as follows.

          No. of moles =

                        =

                        = 0.867 mol

Now, the number of moles of are calculated as follows.

     No. of moles =  

                           =      

                           = 1.07

Therefore, mole fraction of heptane will be calculated as follows.

     Mole fraction =

                           =

                           =

                           = 0.445

Now, we will calculate the partial pressure of heptane as follows.

                 =      

                 = 75.65 torr

Thus, we can conclude that the partial pressure of heptane vapor above this solution is 75.65 torr.

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.