If 120 grams of aluminum oxide reacts with 100 grams of magnesium, which reactant is in excess and by how much? Al2O3 + 3Mg —> 3MgO + 2Al

Limiting reactant is magnesium.

14.1 g remain unreacted.

Explanation:

Hello!

In this case, given the balanced chemical reaction, we are able to compute the moles of each reactant by using their molar masses:

Now, since they are reacting based on a 1:3 mole ratio, we can compute the moles of magnesium consumed by the 1.18 moles of aluminum oxide as follows:

Meaning there are more available moles of magnesium than consumed, and therefore it is the limiting reactant. Moreover, it is in excess by:

It means that 14.1 g of magnesium remain unreacted.

Regards!

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explanation:

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.