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Offlinestrangladesh
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chemistry homework
    #5326493 - 02/21/06 11:23 PM (18 years, 1 month ago)

can some one help out, im haveing a hard time with this class...i think im on the right track but mabey some one can school me really quick...heres the quiz


Chapter 7 Quiz-2
Chemical Formula Relationships

Name__________________________ Date_____________________


(2pts) 1. Which of the following statements is incorrect? C

a) Molecular mass is expressed in amu
b) Formula mass compares the mass of one formula unit of a substance to the mass of one atom of carbon-12
c) Atomic mass has units of grams per atom
d) Both molecular mass and formula mass use carbon-12 as a reference standard
e) Sodium chloride, an ionic compound, is said to have a formula weight, but not a molecular weight


(2 pts) 2. Calculate the formula mass of aluminum carbonate
2-
Al CO
1 3
Al 1x26.98amu 26.98amu
C 1x12.01amu12.01amu
O 3x16.00amu44.00amu
82.99amu


(4 pts) 3. Calculate the percent composition of aluminum oxide
AlO

Al=






(2 pts) 4. How many grams of oxygen are in 8.50 g of formaldehyde, CH2O?

%O g O x 100 = (16.00)g O x 100=
g CH2O 8.50g CH2O


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OfflineAKtoker
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Re: chemistry homework [Re: strangladesh]
    #5326751 - 02/22/06 12:44 AM (18 years, 1 month ago)

1. Looks good to me, but im not 100% sure. Kinda odd wording...

2. Looks good to me.

3. % composition of Aluminum oxide. I'm assuming you want the % of Aluminum? Anyhow, for this one, the total mass is 43 g/mol. Aluminum is about 27 g/mol, so 27/43 x 100% = 62.8% Al by mass.

for the last one,

CH2O is 30 g/mol. 8.50 grams of CH20 would be 0.283 moles. So, multiply 0.283 by 16 g/mol for oxygen, giving you 4.53 grams of Oxygen.

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Offlinestrangladesh
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Re: chemistry homework [Re: AKtoker]
    #5327219 - 02/22/06 06:16 AM (18 years, 1 month ago)

how did you get the totle mass for #3


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Offlinestrangladesh
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Re: chemistry homework [Re: strangladesh]
    #5327227 - 02/22/06 06:23 AM (18 years, 1 month ago)

mabey you could show me how you got those #'s as i am totlely lost.


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OfflineAKtoker
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Re: chemistry homework [Re: strangladesh]
    #5327592 - 02/22/06 10:54 AM (18 years, 1 month ago)

Al is 27amu, oxygen is 16amu (or g/mol). 16+27=43. 27/43 * 100% = 62.8%

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OfflineDocPsilocybin
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Re: chemistry homework [Re: AKtoker]
    #5328152 - 02/22/06 02:01 PM (18 years, 1 month ago)

Sorry but aluminum oxide is Al(2)O(3) meaning the molecular weight of it is 101.96 g/mole. Oxygen is 3*16g/mol=48g/mol. Therefore 48/101.96=~47% of the weight of the molecule.


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