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if the earth's atmosphere is on average roughly 2.3% water vapor, approximately how many molecules of water are present in the atmosphere?

a. 2.3 x 1043
b. 4.3 x 1024
c. 2.3 x 1020
d. 4.3 x 1020
e. 2.3 x 1024
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Given the following densities at 25°C magnesium: 1.7 g/cm3 graphite: 1.8 g/cm3 iron: 7.9 g/cm3 A block of iron has a mass of 819 g. What is the mass of a block of magnesium that has the same volume as the block of iron?

a. 1.1 x 103 g
b. 2.8 x 103 g
c. 1.8 x 102 g
d. 3.8 x 103 g
e. none of these
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A sample of a liquid with a density of 2.1 g/mL has a weight of 4.242 g. The volume of the liquid is:

a. 2.0 mL
b. 2.02 mL
c. 2 mL
d. 2.020 mL

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The following calculation, (0.10 m)(1.0 x 10-4 km)(0.1 x 102 cm), can also be expressed as all of the following except:

a. (10 cm)(10 cm)(10 cm)
b. 1 L
c. 1000 mm
d. 103 cm3
e. 1000 mL
(I got A for this one...)
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Can someone please show me steps?

2007-01-18 04:02:08 · 6 answers · asked by Anonymous in Science & Mathematics Mathematics

I am in college.....I thought this was a place for help. I needed to check my answers.

2007-01-18 04:13:06 · update #1

6 answers

1) I'd pick (a), although I don't have the references handy. Reason being: You'd need the volume of the atmosphere, average density, and average temperature. Unless these are known, you cannot actually calculate the answer. I chose (a) because it is the only one in the range of magnitude needed; 1 mole (roughly 18g) of water contains 6.23 X 10^23 molecules (Avogadro's number) and would be the approximate amount in the air in a large room. So 10^43 is the only given answer large enough to be valid for the entire atmosphere.

2) Density is mass/volume, so volume = mass/density. The iron block has a volume of 819/7.9 = 103.7cm3. (If you pay attention to significant digits, this would be rounded to 104 cm3.) None of the given options contain either the correct volume (104cm3) or the given density of magnesium (1.7g/cm3) so (e) is the correct answer.
(Addendum: If you're being really picky, the volume of the block is rounded to 100 or 1.0X10^2 cm3; if the notation in the given answers is supposed to be 10^3 and 10^2 instead of 103 or 102, then (c) is the *closest* to the correct answer; but it still does not have the given density for magnesium - unless that's another typo.)

3) The answer you'll get on a calculator is 2.02cm3, but because the density is only given to 2 significant digits you have to round off the answer to 2.0; therefore (a) is the correct answer.

4) Again, because of rounding to significant digits, all components reduce to 10cm. Assuming option (d) is supposed to mean 10^3 cm3, only option (c) is invalid because it has units of length instead of volume.

PS - It appears that you're in the first segment of a chemistry course. The focus during the introductory phase is on learning measurements, magnitude, notation, significant digits, notation of units, etc. - the language of science, in other words. These are important skills which you will be using throughout the course.

2007-01-18 04:29:53 · answer #1 · answered by dukefenton 7 · 0 0

1. Since I don't no the entire mass of the atmosphere I can't work it out, I can tell you there are 6.02 x 10^23 molecules within a particular compound.

2. Don't know

3. Density = mass/volume

So volume = mass / density

You say the "weight" of the liquid, this is not the same as the mass, so if you meant the mass then ...

V = 4.242 / 2.1

V = 2.02mL

4. If you were doing some rough rounding of the decimal places you could say A was the correct answer, but in fact the correct answer is 1020 cm^3

2007-01-18 05:23:18 · answer #2 · answered by Anonymous · 0 0

Do your own damn homework. Wait, it's lunch time so you should still be at school. Ask your teacher! Your taxes are paying for their salary anyways, so take advantage of them by bugging them during their lunch break!

2007-01-18 04:12:07 · answer #3 · answered by Anonymous · 0 0

I came up with 2 apples.

2007-01-18 04:05:06 · answer #4 · answered by Anonymous · 1 0

You don' t get them because your not asking your teacher for help and doing it yourself.

2007-01-18 05:12:04 · answer #5 · answered by Anonymous · 0 0

Vortex!!

2007-01-18 04:04:56 · answer #6 · answered by Twigward 3 · 1 0

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