This is Raoult law & vapor pressure problem: high school

2.7 moles of Tang are added to a pitcher containing 3.28 liters of H2O at a temperature of 25°C. The vapor pressure of water alone is 23.8 mm Hg at 25o C. What is the new vapor pressure of the Tang solution?

23.5 mmHg

Explanation:

As per Rault's law, when a solute is dissolved, the vapor pressure of the solution is equal to the product of the mole fraction of the solvent and  the vapor pressure of the pure solvent.

       

1. Calculate the mole fraction of solvent

       

a) Moles fo solvent

The solven is water

3.28 liters of H₂O = 3,280 g of H₂O (taking density equal to 1.000 g/mol.number of moles = mass in grams/molar massmolar mass of H₂O = 18.015 g/molnumber of moles of H₂O = 3,280g / (18.015g/mol) =  182.07 mol

b) Moles of solute

The solute is tang:

2.7 mol (given)

c) Mole fraction of solvent:

         

2. Vapor pressure of the solution

     

gas

explanation:

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Answer: abeexplanation:

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.