Copper has two naturally occurring isotopes, 63cu (isotopic mass 62.9296 amu) and 65cu (isotopic mass 64.9278 amu). if copper has an atomic mass of 63.546 amu, what is the percent abundance of each isotope? report your answer to 5 significant figures.

Percentage of first isotope = 69.152 %

Percentage of second isotope =  30.848 %

Explanation:

The formula for the calculation of the average atomic mass is:

Given that:

For first isotope:

Let % = x %

Mass = 62.9296 amu

For second isotope:

% = 100 - x  %  (Since, there are only two isotopes)

Mass = 64.9278 amu

Average mass = 63.546 amu

Thus,  

Solving,

1.9982 x = 138.18

Thus,

Percentage of first isotope = x = 69.152 %

Percentage of second isotope = 100 - x % = 30.848 %

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

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