When 19g of a certain molecular compound X are dissolved in of benzonitrile , the freezing point of the solution is measured to be . Calculate the molar mass of X.

The given question is incomplete. The complete question is:

When 19 mg of a certain molecular compound X are dissolved in 200 g of benzonitrile , the freezing point of the solution is measured to be . Calculate the molar mass of X. Freezing point of pure benzonitrile =

Molar mass of X is 1271 grams

Explanation:

Depression in freezing point =

Mass of solute (X) = 19 g

Mass of solvent (benzonitrile) = 200.0 g = 0.2 kg (1 kg = 1000 g)

Formula used :  

where,

= change in freezing point =

i = Van't Hoff factor = 1

= freezing point constant = 5.35 K.kg/mole

m = molality

Now put all the given values in this formula, we get

Thus molar mass of X is 1271 grams

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.