20 Liters of a mixture of N2 gas and CH4 gas was made up with a pressure of 700. Mm Hg and a temperature of 300. C. If the partial pressure of N2 gas was 250. Mm Hg, how many grams of CH4 were added to the mixture?

4.04g of CH₄ are in the mixture

Explanation:

In a mixture of gases, the total pressure is equal to partial pressure of each gas in the mixture.

In the problem, total pressure is 700mmHg and there are just 2 gases (N₂ ans CH₄) where the partial pressure of N₂ is 250mmHg. Thus, pressure of CH₄ is:

700mm Hg - 250mm Hg = 450mmHg. In atm:

450 mmHg ₓ (1 atm / 760mm Hg) = 0.5921 atm

Using PV = nRT

Where P is pressure (0.5921atm), V is volume (20L), R is gas constant (0.082atmL/molK), T is absolute temperature (300°C + 273.15 = 573.15K), it is possible to obtain moles -n- of the gas, thus:

PV / RT = n

0.5921atm×20L / 0.082atmL/molK×573.15K = n

0.252 moles CH₄ = n

As molar mass of CH₄ is 16.04 g/mol:

0.252 moles CH₄ × (16.04g / 1mol) = 4.04g of CH₄ are in the mixture

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.