A method of lowering the concentration of HCl(aq) is to allow the solution to react with a small quantity of Mg. How many milligrams of Mg must be added to 219 mL of 1.032 M HCl to reduce the solution concentration to exactly 1.000 MHCl

85.07 mg of Mg must be added

Explanation:

The reaction of HCl(aq) with Mg is:

2HCl(aq) + Mg → MgCl₂ + H₂

219 mL of 1.032 M HCl are:

0.219L × (1.032mol / L) = 0.226 moles of HCl

As you want to reduce the concentration to 1.000M HCl and volume of solution is 0.219L, moles of HCl you want are 0.219 moles

That means you need to make react:

0.226 moles - 0.219 moles = 7x10⁻³ moles of HCl

Based on the reaction, 2 moles of HCl react with 1 mol of Mg, that means you need:

7x10⁻³ moles of HCl ₓ (1 mol Mg / 2 mol HCl) = 3.5x10⁻³ moles of Mg. In miligrams:

3.5x10⁻³ moles of Mg ₓ (24.305g / 1mol) ₓ (1000 mg / 1g) =

85.07 mg of Mg must be added

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.