Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: sundrops on January 21, 2005, 02:04:37 AM
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The green pigment chlorophyll a, absorbs red light, the energy from which powers photosynthetis processes in plants and algae.
Chlorophyll a is 6.27% nitrogen by mass.
Each molecule of chlorophyll a contains 4 nitrogen atoms.
What is the molecular mass of chlorophyll a?
I'm really confused, I don't even know how tio attack this question - I mean I don't know what chlorophyll is made up of - it doesn't seem like there's enough info. Please *delete me*
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What is the mass of 4 Nitrogens?
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mass of 4 nitrogens would be 14.01 * 4 = 56.04g
right? but how does that help me?
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That was the mass of 6.27% of the molecule.
What is the mass of the other 93.73% of the molecule? Then calculate the total mass for 1 molecule.
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OH! that makes sense! but the mass of the rest of the rest of the molecule isn't given! thats what makes this question sooo hard! not enough information. its frusterating!!
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how do i find the mass of the other 93.73% of the molecule?
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6.27/56.04 = 100/x
where x is the molecular mass of chlorophyl
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oh - that makes sense :D
thanks so much!
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now what if the chlorophyll molecule contains 1 magnesium atom.
what mass of magnesium is to be found in 2.97 g of chlorophyll?
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how would i go about trying to solve that?
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It wouldn't matter.
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but that's part II of the question - i need to figure it out somehow. I need to find out how much magnesium is in 2.97 g of chlorophyll - how would i go about doing that?
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you already have the total mass of chlorophyl, so the mass of 1 magnesium atom is what percent of that total mass?
start from there ;)
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ok so if percent nitrogen is 6.27% and the mass of nitrrogen is 56.04g
then with the mass of 1 magnesium atom being 24.31g - then it's percentage of the total mass would be 2.72% !! ;D
that makes sense!
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now, how would I apply that information into determinig how much magnesium I would find in 2.97g of chlorophyll? :-\
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check your givens and write them down
2.97 grams of chlorophyll
900 g/mol chlorophyll
24.31 g/mol of magnesium
percent of magnesium
as far as i remember, you can either use percent calculation or follow stoichiometry
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thanks for everyones input - i finally figured it out! ;D (finally!) ouch - my head really hurts now... ::)