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answers to exam 1

# answers to exam 1 - Solutions 1 Solution Do not get hung up...

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Solutions 1 Solution: Do not get hung up thinking “Hey, we never did one like this before!” Think in terms of relationships. To Find You need atoms moles and N A moles mass and atomic mass So the problem becomes more clear once you identify the relationships. atoms moles N A atoms grams atomic mass N A So now we know what we are looking for. We need the mass of the iron metal! Let’s see if we can find that from the density. Density has units g/cm 3 . For iron the density is 7. 9 g/cm 3 . How can we use this to get grams? Let the units guide you. To get the mass of iron metal it looks like we just need to multiply density by cm 3 which is a unit of volume. mass g 7. 9 g/cm 3 sphere volume cm 3 7. 9 g/cm 3 4 3 4.0 in 2 2.54 cm/in 3 4338. g Don’t forget the inch to cm conversion! Now that we have the mass we can find moles and atoms. We have already written the formula we need. atoms grams atomic mass N A 4338. g 55. 85 g/mol 6.022 10 23 atoms/mole 4. 678 10 25 atoms 2 Solution: The thin sheet looks like a cylinder that is 1 atom high. The volume is V r 2 h 1. 1 cm 3 where h is the diameter of the atom. We are asked to find the diameter of the thin sheet. d 2 2 h 1. 1 cm 3 The thickness of the thin metal sheet is equal to the diameter of the atom. h 2. 78 Å

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