chapter 2 atoms, molecules and ions. formula weight & molecular weight the formula weight of a...
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Formula Weight & Molecular Weight
• The FORMULA WEIGHT of a compound equals the SUM of the atomic masses of the atoms in a formula.
• If the formula is a molecular formula, the formula weight is also called the MOLECULAR WEIGHT.
The MOLE
• Amount of substance that contains an Avogadro’s number (6.02 x 10 23)of formula units.
The MOLE
• The mass of 1 mole of atoms, molecules or ions = the formula weight of that element or compound in grams. Ex. Mass of 1 mole of water is 18 grams so molar mass of water is 18 grams/mole.
Formula for Mole
Mole = mass of element formula weight of
element
Sample Mole Calculations
1 mole of C = 12.011 grams» 12.011 gm/mol
• 0.5 mole of C = 6.055 grams» 12.011 gm/mol
Avogadro’s Number
•Way of counting atoms
• Avogadro’s number = 6.02 x 1023
Point to Remember
One mole of anything is 6.02 x 1023 units of that substance.
And……..
• 1 mole of C has the same number of atoms as one mole of any element
Formula Weight & Molecular Weight
• The FORMULA WEIGHT of a compound equals the SUM of the atomic masses of the atoms in a formula.
• If the formula is a molecular formula, the formula weight is also called the MOLECULAR WEIGHT.
Summary
• Avogadro’s Number gives the number of particles or atoms in a given number of moles
• 1 mole of anything = 6.02 x 10 23 atoms or particles
Sample Problem 2
• Compute the number of atoms and moles of atoms in a 10.0 gram sample of aluminum.
Solution
• PART I:• Formula for Mole:
–Mole = mass of elementatomic mass of element
Solution (cont.)
• Part II: To determine # of atoms
• # atoms = moles x Avogadro’s number
Problem # 2
• A diamond contains 5.0 x 1021
atoms of carbon. How many moles of carbon and how many grams of carbon are in this diamond?
Molar Mass• Often referred to as molecular mass–Unit = gm/mole
• Definition: –mass in grams of 1 mole of the
compound
Example Problem
• Determine the Molar Mass of C6H12O6
Solution
• Mass of 6 mole C = 6 x 12.01 = 72.06 g• Mass of 12 mole H = 12 x 1.008 = 12.096 g• Mass of 6 mole O = 6 x 16 = 96.00 g
•Mass of 1 mole C6H12O6
= 180.16 g
Problem #3
•What is the molar mass of (NH4)3(PO4)?
Molar Mass• Often referred to as molecular mass–Unit = gm/mole
• Definition: –mass in grams of 1 mole of the
compound
Sample Problem• Given 75.99 grams of (NH4)3(PO4), determine the ff:• 1. Molar mass of the compound• 2. # of moles of the compound• 3. # of molecules of the compound• 4. # of moles of N• 5. # of moles of H• 6. # of moles of O• 7. # of atoms of N• 8. # of atoms of H• 9. # of atoms of O