General Chemistry - Conversions Help!

[skyisblue]

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I don’t quite understand the logic in solving this problem. Here goes:

One carrot may contain 0.75mg of vitamin A, C20H30O. How many hydrogen atoms are in 0.75mg of Vitamin A? What mass of Hydrogen is this?

According to the book, the answer for the number of hydrogen atoms is 4.8 x 10 to the 19th atoms.

Since the mass of 1 H atom is 1.0g, I would think that the mass of this amount of hydrogen atoms would be the same as the number of atoms of hydrogen . However, this is not the case. The book solves it by dividing the number of H atoms with Avogadro’s number and then multiplying by Molar Mass of Hydrogen. The answer is 8.0 x 10 to the negative 5 grams. Why is the answer not 4.8 x 10 to the 19th grams?????

 

[lilchinoboy03]

i think what ur missing here is that molar mass is per mole. So it is 1 g per mole of H. And 1 mole is defined by Avogadro's numer as 6.022 x 10^23 or something close to that. Feel free to correct me if it's me that is off somewhere, but I think that's what's going on here.

Easy mistake to make. Don't worry about it. A good way to do this is to actually write out the whole conversion in one long multiplication product including units and make sure everything cancels out the way you want.

 

[Vapor1122]

Since the mass of 1 H atom is 1.0g...Why is the answer not 4.8 x 10 to the 19th grams?????

Think about your answer. 4.8 x 10^19 g is several trillion tons

And one H atom doesn't weight a gram. That'd be about the weight of a playing card.

A lot of times it's easy to screw up like that. Thinking about whether your answer makes practical sense is a good check.