Chemistry, 26.02.2020 23:24 aaa813

FCC lead has a lattice parameter of 0.4949 nm and contains one vacancy per 500 Pb atoms. Calculate (a) the density; and (b) the number of vacancies per gram of Pb.

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Answer from: jenna6891

Explanation:

(a) Number of atoms present in FCC are 4 atoms. Hence, number of atoms present in the given cell are as follows.

No. of atoms/cell = $4 \times \frac{499}{500}$

= 4

Density will be calculated as follows.

Density = $\frac{ZM}{Na^{3}}$

= $\frac{4 \times 207}{6.023 \times 10^{23}} \times (0.4949 \times 10^{-7})^{3}$

= 11.34 $g/cm^{3}$

Therefore, density of the given substance is 11.34 $g/cm^{3}$ .

(b) Now, there is 1 vacancy present for every 500 lead (Pb) atoms. Therefore, 500 Pb atoms occupied by four lattice points is as follows.

$\frac{500}{4}$

= 125 unit cells

$\frac{\frac{1}{125}}{(0.4949 \times 10^{-7})^{3}} \times \frac{1}{11.34 g/cm^{3}}$

= $5.82 \times 10^{18}$

Thus, we can conclude that number of vacancies present per gram are $5.82 \times 10^{18}$ .

Answer from: Quest

How do we find the answer?

Answer from: Quest

Answer: abeexplanation:

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.

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FCC lead has a lattice parameter of 0.4949 nm and contains one vacancy per 500 Pb atoms. Calculate (...

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