Do sample problem 13.8 in the 8th ed silberberg book. you add 1.4 kg of ethylene glycol (c2h6o2) antifreeze to 4,192 g of water in your car's radiator. what is the boiling point of the solution? the kb for water is 0.512 °c/m. enter to 2 decimal places.

The solution boils at 102.76 °C

Explanation:

Δt = m* Kb x i  

i = 1 with 1 particle in solution

m = molality

Kb = 0.512 °C/molal

Step 2: Calculate moles C2H6O2

molar mass of  C2H6O2 = 62.068 g/mol

Calculate number of moles:

Moles = Mass / molar mass

Moles = 1400 grams / 62.068 g/mol

Moles C2H6O2 = 22.56 moles

Step 3: Calculate molality

these are in 4192 g of water:

22.56 moles / 4.192 kg water

⇒ moles / kg of water = 5.38 moles / Kg = m olal

Step 4: Calculate  ΔT

ΔT= Kb * molal = 5.38 molal* 0.512 °C/m

ΔT = 2.76 °C

Boiling point = 100°C + 2.75 °C = 102.76 °C

the solution boils at 102.76 °C

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.