How many grams of sodium chloride decompose to yield 15 grams of chlorine gas? 2NaCl → 2Na+ Cl2
A- 12.363 9 Naci
B- 49.453 g Naci
C- 30 g NaCl
D- 0.846 g Naci

24.6g of NaCl

Explanation:

Expression of the reaction:

            2NaCl →  2Na  +  Cl₂

Given parameters:

Mass of Cl₂  = 15g

Unknown:

Mass of NaCl  = ?

Solution:

To solve this problem, we have to use mole relationships.

 Find the number of moles of the mass of the given specie;

    Number of moles  =  

     Molar mass of Cl₂  = 2(35.5) = 71g/mol

   Number of moles  =   = 0.21mole

Now;

 From the balanced reaction equation;

        1 mole of Cl₂ is produced from 2 moles of NaCl;

      0.21 mole of Cl₂ will be produced from 0.21 x 2 = 0.42mole of NaCl

So,

  Mass of NaCl = number of moles x molar mass

    Molar mass of NaCl  = 23 + 35.5 = 58.5g/mol

 Mass of NaCl  = 0.42 x 58.5 = 24.6g of NaCl

a. a primary source combines several different accounts of an event. b. a primary source generally benefits from having been written after an event.

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.