Calculating Moles of Fe in 400.0g of Iron

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In summary, the conversation is about finding the number of Fe atoms and moles of Fe atoms in 400.0 g of iron. The person attempted to solve the problem by using a proportion and got an answer of 7.17 moles, but it was marked wrong. They tried changing the number of significant figures and using a more accurate atomic weight, and were able to get the correct answer.
  • #1
name_ask17
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Homework Statement



How many Fe atoms and how many moles of Fe atoms are in 400.0 g of iron?



The Attempt at a Solution



Ok. i attempted to find the number of moles by using 400/55.8 to get 7.17 but that is wrong?! please tell me ehy this is wrong. i set up a proportion like this 55.8g Fe = 1 mol
all over 400.0 grams =x and i solved for that x. i know its wrong, but why?
 
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  • #2


name_ask17 said:
Ok. i attempted to find the number of moles by using 400/55.8 to get 7.17 but that is wrong?! please tell me ehy this is wrong. i set up a proportion like this 55.8g Fe = 1 mol
all over 400.0 grams =x and i solved for that x. i know its wrong, but why?
Beats me. I would have said that's exactly what you're supposed to do. How do you know it's wrong? Were you given a different number as the solution?

By the way, the phrasing "How many moles of Fe atoms..." is peculiar. Normally one just asks "How many moles of Fe..." If you answer is wrong, then perhaps it is because your prof is making some unusual subtle distinction by including the word "atoms" in the second part of the question.
 
  • #3


Perhaps your answer is not being counted as correct because 400.0g has four significant digits, and your answer should have four significant figures as well.
 
  • #4


well i know its wrong because my online homework is marking it wrong. I am really confused because i even tried changing the number to 4 sigfigs instead of 3 but it was wrong again. What am i doing wrong?!
 
  • #5


name_ask17 said:
well i know its wrong because my online homework is marking it wrong. I am really confused because i even tried changing the number to 4 sigfigs instead of 3 but it was wrong again. What am i doing wrong?!
Maybe you should try a more accurate number for the atomic weight of iron. Also, what about the number of atoms question?
 
  • #6


you are right! thank you. i used a more specific number and i got the correct answer. and i just multuplied by avagadros number for atoms. thanks for all your help, everyone.
 
  • #7


thanks!
 

1. How do you calculate the number of moles of Fe in 400.0g of Iron?

To calculate the number of moles of Fe in 400.0g of Iron, you would first need to determine the molar mass of Iron, which is 55.845 g/mol. Then, divide the given mass of Iron (400.0g) by the molar mass (55.845 g/mol). This will give you the number of moles of Fe in 400.0g of Iron.

2. What is the formula for calculating moles of Fe?

The formula for calculating moles of Fe is: number of moles (n) = mass (m) / molar mass (M). This formula can be rearranged to solve for any of the three variables, depending on the given information.

3. Why is it important to calculate moles of Fe?

Calculating moles of Fe is important because it allows us to relate the mass of a substance to its chemical quantity. This helps us understand the amount of a substance present in a given sample and can be used to predict and measure chemical reactions.

4. Can the same formula be used to calculate moles of Fe in any sample of Iron?

Yes, the same formula can be used to calculate moles of Fe in any sample of Iron, as long as the molar mass of Iron is used consistently. However, if the Iron sample is not pure, the molar mass may need to be adjusted to account for the other elements or compounds present.

5. What units are used for moles of Fe?

The unit for moles of Fe is mol. This unit represents the amount of a substance that contains the same number of entities (atoms, molecules, or ions) as there are atoms in 12 grams of Carbon-12. It is a unit of measurement commonly used in chemistry to quantify the amount of a substance present.

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