Chris the chemist works in a laboratory in which the temperature is maintained at a constant 25oc and the pressure is always 100 kpa. chris needs to analyse some calcium carbonate, caco3(s), to determine whether it is pure or has been contaminated. chris will analyse the calcium carbonate by taking a small 0.00500 mole sample and adding hydrochloric acid, hcl(aq), to it until all the calcium carbonate has disappeared and no more carbon dioxide gas, co2(g), is produced. as the gas is produced it will be collected by a water displacement method. the balanced chemical equation for this reaction is known to be: caco3(s) + 2hcl(aq) → cacl2(aq) + co2(g) + h2o(l) if the sample is pure, what volume of carbon dioxide gas will be collected?

The given balanced chemical equation:

Calculating the moles of carbon-dioxide:

Given, moles of

Moles of

Using the ideal gas equation to find out volume from moles, pressure and temperature:

PV = nRT

V = 0.124 L or 124 mL

Therefore, 124 mL of carbon dioxide will be collected.

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.

i'm wiling to try and you : )