# Could you determine the amount of atoms in a substance? - PowerPoint PPT Presentation

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Could you determine the amount of atoms in a substance? How do scientists count when atoms and molecules are so small?. Using the concept of counting by weight Could you determine the amount of atoms in a piece of copper?. What information would you need?.

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Could you determine the amount of atoms in a substance?

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#### Presentation Transcript

Could you determine the amount of atoms in a substance?

How do scientists count when atoms and molecules are so small?

## What information would you need?

The periodic table has a secret! It can tell you the amount of atoms in a specific mass of each element

• Look at the amu of copper. The amu also describes the number of atoms in a specific mass in g

• Ex: There are 6.02 X10 23 atoms/63.546 g of copper

• Could you determine the amount of atoms in any piece of Copper?

• 6.02 X10 23 is a huge number!!!

• It is a unit of measurement that scientists use. Just as chefs use the dozen (12)

• This is manageable because atoms are so tiny

• They call this number a mole!! (sometimes abbreviated mol)

• With this new information could you determine the amount of moles if I gave you a specific mass of an element?

• Write a conversion you could use.

• Ex If I have .500g Al 1mol/26.98g How many mols do I have try it…

• .500g Al 1 mol/26.98g = .0185 mols of Al

• If I gave you the amount of mols could you give me the mass?

• .496 mols of Al 26.98g Al/1 mol = 13.4 g Al

• If I gave you the number of atoms could you determine the mass?

• Remember there are 6.02 X10 23 atoms in a mol and the molar mass is the mass of one mole

• Find the mass of 2.03 X10 23 atoms of S

• 2.03 X10 23 atoms S 1 mol/6.02 X 10 23 atoms S 32.055g S/1 mol

• Answer = 10.8 g S

The number on the periodic table is called the MOLAR MASS. This gives you the mass in one mole of a substance.

Find the molar mass of O,S,N,F

Find the molar mass of H2O, HF

### Can you find the mass of a particular amount of atoms?

Find the mass of 2.03 X10 23 atoms of S

2.03 X10 23 atoms S 1 mol/6.02 X 10 23 atoms S 32.055g S/1 mol

### Moles from Atoms?

• Could you determine the amount of moles if I gave you the amount of atoms?

• 3.02 X 10 23 atoms of Ca is how many moles?

• 3.02 X10 23 atoms Ca 1 mol/ 6.02 X 10 23 atoms Ca = .502 mols Ca

### Could you determine the amount of atoms in a specific amount of moles?

• 2.3 mols of Sr

• 2.3 mols 6.02 X 10 23 atoms/1 mol = 1.4 X 10 24 atoms

### How about the number of atoms in a specific amount of mass?

• 345 g of Ca

• 345 g Ca 1 mol/40.078g 6.02 X 10 23 atoms/1 mol