What is the mole fraction of lif in an aqueous soltion that contains 39.4% lif

mole fraction (LiF)=

= (number of mole LiF)/(number of mole LiF + number of mole H2O)

In 100 g solution there are 39.4 g LiF and 100-39.4 = 60.6 g H2O.

1.

M(LiF) = 6.94 +19.00 = 25.94 g/mol

39.4 g LiF*1mol LiF/25.94 g LiF = 1.519 mol LiF

2.

M(H2O) = 2*1.01 + 16.00 = 18.02 g/mol

60.6 g H2O*1 mol H2O/18.02 g H2O = 3.363 mol H2O

3.

mole fraction (LiF)=

= (1.519 mol LiF)/(1.519 LiF + 3.363 mol H2O) = 0.311

mole fraction (LiF)=0.311

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6

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.