Aqueous lithium hydroxide reacts with aqueous aluminum nitrate. if the reacting solutions contain 120.0 grams of reactant, how much precipitate is made, theoretically, and what mass of excess reactant remains?

The moles of each reagent present will be calcualted as

Moles = mass / molar mass

a) Mass of LiOH given = 120 g

Molas mass of LiOH = 24 g / mol

Moles of LiOH = 120 / 24 = 5 moles

b) mass of  Al(NO3)3 = 120 g

Molar mass = 213 g/mol

moles of Al(NO3)3 = 120 g / 213 = 0.56

The reaction between lithium hydroxide and aluminium nitrate will be

3LiOH (aq)  + Al(NO3)3(aq)   > 3LiNO3(aq)  + Al(OH)3 (s)

So here for three moles of LiOH we need one mole of Al(NO3)3 to form one mole of Al(OH)3

So with 5 moles of LiOH we need = 5/3 moles of Al(NO3)3 = 1.67 moles o Al(NO3)3

However we have only 0.56 moles of Al(NO3)3

Thus here Al(NO3)3 is the limiting reagent

1 mole of Al(NO3)3 will react with three moles of LiOH to give one mole of  Al(OH)3

0.56 moles of Al(NO3)3 will react with 0.56 X 3 moles of LiOH to give 0.56 moles of Al(OH)3

Mass of Al(OH)3  formed = moles X molar mass = 0.56 X 78 = 43.68 g

Moles of LiOH left = 5 - (3*0.56) = 3.32 moles

Mass of LiOH left = moles X molar mass = 3.32 X 24 = 79.68 g

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.