How would you prepare 500 cm3 of 2.0 M solution of Na2CO3 solution from its anhydrous salt? [C = 12, O = 16, Na = 23

The answer to your question is given below

Explanation:

We'll begin by converting 500 cm³ to L. This can be obtained as follow:

1000 cm³ = 1 L

Therefore,

500 cm³ = 500 cm³× 1 L / 1000 cm³

500 cm³ = 0.5 L

Next, we shall determine the number of mole of Na₂CO₃ in the solution. This can be obtained as follow:

Volume = 0.5 L

Molarity = 2 M

Mole of Na₂CO₃ =?

Molarity = mole /Volume

2 = Mole of Na₂CO₃ / 0.5

Cross multiply

Mole of Na₂CO₃ = 2 × 0.5

Mole of Na₂CO₃ = 1 mole

Finally, we shall determine the mass of 1 mole of Na₂CO₃. This can be obtained as follow:

Mole of Na₂CO₃ = 1 mole

Molar mass of Na₂CO₃ = (23×2) + 12 + (16×3)

= 46 + 12 + 48

= 106 g/mol

Mass of Na₂CO₃ =?

Mass = mole × molar mass

Mass of Na₂CO₃ = 1 × 106

Mass of Na₂CO₃ = 106 g

Thus, to prepare the solution, weigh 106 g of Na₂CO₃ and dissolve in 500 cm³ (i.e 0.5 L) of water.

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.