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***NEED CHEM HELP QUICK***

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Yeezus
Posts: 3350 - Karma: 469
ok im doing my chem homework but i dont understand it at all and you guys are my last hope so any help would be appreciated. how would u find this out

How many Ca atoms are there in 0.800g of Ca?

How many Cl2 molecules are there in 79.3g of Cl2

How many Cl atoms are there in 79.3g of Cl2

thanks for any help
Feb 23 2010 9:23PM
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wiener
Posts: 2247 - Karma: 63
just use molecular mass and Avagadro's number and BAM

molecular mass is grams/mole

Avagadros number is atoms/mole

work out your units

units units units
Feb 23 2010 9:26PM
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butteredpretzel
Posts: 1485 - Karma: 866
just check da periodic table and uses kind wieners advice
Feb 23 2010 9:27PM
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Yeezus
Posts: 3350 - Karma: 469
so this is what i got out of it

.800/40.078= .020

.020 x 6.022 x 10^23 = 1.204 x 10^23

but thats most likely wrong.
Feb 23 2010 9:33PM
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wiener
Posts: 2247 - Karma: 63
i think that is right on a glance.

put in your units and if they cancel and give you atoms then you are good but it does look right
Feb 23 2010 9:35PM
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Style+eeze
Posts: 6901 - Karma: 551
This... And, no matter how annoying it is, dimensional analysis can help a lot as far as the organization of the problem goes.
Feb 23 2010 9:38PM
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ohpatti
Posts: 745 - Karma: 25
didnt you get equations with that ish?
Feb 23 2010 11:48PM
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b-kul
Posts: 4350 - Karma: 1,111
so happy i am done with chem forever.
Feb 24 2010 12:08AM
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Scott0_robot0
Posts: 3291 - Karma: 212
i believe that thats right. i think dont feel like looking into it further ha
Feb 24 2010 12:12AM
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chapz
Posts: 10182 - Karma: 66
1)

0.8g*(1mol/12.01g)*(6.02*10^23/1mol) = 4.01*10^22 atoms

2)

79.3g*(1mol/70.9g)*(6.02*10^23/1mol) = 6.73*10^23 atoms

3)

79.3g*(1mol/35.45g)*(6.02*10^23/1mol) = 1.35*10^24 atoms



(2) might be wrong. the last time i did this was first year of cegep. i forget what to do with diatomic elements!
Feb 24 2010 12:19AM
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chapz
Posts: 10182 - Karma: 66
FUCK>
Ca is calcium, not carbon. duh. i feel blonde.

the answer would be

1.202*10^22 atoms
i think.
Feb 24 2010 12:21AM
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BigJew
Posts: 6974 - Karma: 79
Yep. Dimensional analysis is the key.

Feb 24 2010 12:27AM
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Style+eeze
Posts: 6901 - Karma: 551
at first i hated it, because at the beginning of chem i could do a lot of the math stuff in my head (along with my peers that are in higher level math classes), but i soon realized how much nicer it is.

Molecules to Moles:

__Molecules I          1 Mole
------------------------------------------
           1        I Avagadro's Number

Moles to Molecules:

__Molecules I Avagadro's Number
------------------------------------------
           1        I           1 Mole

Mass to Moles:

__Grams I              1 Mole
-----------------------------------------
        1      I          Molar Mass

Moles to Mass:

__Moles I Molar Mass
---------------------------
        1    I   1 Mole

There you go, my friend, straight out of my notes.  Use DA and pass chem!
Feb 24 2010 1:44AM
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squibble
Posts: 4569 - Karma: 104
HIGH SCHOOL IS A BREEZE
Feb 24 2010 2:27AM
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