Practice problem question - need help

Swenis

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Hey guys, I'm a pre-pharm here at UNC-Asheville. I'm in general chem 1 at the moment and have been doing some practice problems on my own time to help me prepare for my test here in a couple of weeks. Well, anyways, I need help on a particular problem and, since I live off campus, I have no way of getting in touch with my classmates. If anyone could help me with this, I would be very thankful! I have the answer sheet that the book came with, but I just don't know how to get there using dimensional analysis. If this is against the rules, I apologize.

A sample of glucose, C6H12O6, contains 5.77E20 atoms of carbon.

A) How many atoms of hydrogen does it contain? (I know it's just twice as much, but how do I set up the analysis?) ANS: 1.15E21 H atoms

B) How many molecules of glucose does it contain? ANS: 9.62E19 C6H12O6 molecules

C) What is the mass of this sample in grams? ANS: .0287g C6H12O6

Thanks everyone!

teachtopharm?

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Swenis said:
Hey guys, I'm a pre-pharm here at UNC-Asheville. I'm in general chem 1 at the moment and have been doing some practice problems on my own time to help me prepare for my test here in a couple of weeks. Well, anyways, I need help on a particular problem and, since I live off campus, I have no way of getting in touch with my classmates. If anyone could help me with this, I would be very thankful! I have the answer sheet that the book came with, but I just don't know how to get there using dimensional analysis. If this is against the rules, I apologize.

A sample of glucose, C6H12O6, contains 5.77E20 atoms of carbon.

A) How many atoms of hydrogen does it contain? (I know it's just twice as much, but how do I set up the analysis?) ANS: 1.15E21 H atoms

B) How many molecules of glucose does it contain? ANS: 9.62E19 C6H12O6 molecules

C) What is the mass of this sample in grams? ANS: .0287g C6H12O6

Thanks everyone!

Hope this helps! I will try to type this in as best as I can:

A) (5.77E20 C atoms) * (12 H atoms / 6 C atoms) = 1.15E21 H atoms

B) (5.77E20 C atoms) * (1 glucose molecule / 6 C atoms) = 9.62E19 glucose molecules

C) C Atomic weight = 12.0107 g/mole * 6 C atoms = 72.0642
H Atomic weight = 1.00794 g/mole * 12 H atoms = 12.09528
O Atomic weight = 15.9994 g/mole * 6 O atoms = 95.9964

72.0642 + 12.09528 + 95.9964 = 180.1558 g/mole of glucose

(180.1558 g / mole glucose) * (1 mole / 6.022E23 glucose molecules) * (9.62E19 glucose molecules) = 0.0288 g glucose

(I don't know why I got 0.0288 g instead of 0.0287 g. Maybe used more precise atomic weights)

Swenis

Member
10+ Year Member
5+ Year Member
teachtopharm? said:
Hope this helps! I will try to type this in as best as I can:

A) (5.77E20 C atoms) * (12 H atoms / 6 C atoms) = 1.15E21 H atoms

B) (5.77E20 C atoms) * (1 glucose molecule / 6 C atoms) = 9.62E19 glucose molecules

C) C Atomic weight = 12.0107 g/mole * 6 C atoms = 72.0642
H Atomic weight = 1.00794 g/mole * 12 H atoms = 12.09528
O Atomic weight = 15.9994 g/mole * 6 O atoms = 95.9964

72.0642 + 12.09528 + 95.9964 = 180.1558 g/mole of glucose

(180.1558 g / mole glucose) * (1 mole / 6.022E23 glucose molecules) * (9.62E19 glucose molecules) = 0.0288 g glucose

(I don't know why I got 0.0288 g instead of 0.0287 g. Maybe used more precise atomic weights)

Thank you!!!

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You're welcome!

Requiem

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Yeah they probably rounded to 3 places after the decimal. That just reminded me of my chem labs
no fun.

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