The Mole

1. The Mole (no, it’s not an animal!)

2. The Mole • It is a quantity, like a dozen, a trio, a pair • It is used to measure a quantity of very small objects, i.e., atoms and molecules • It is 6.02 x 1023, also known as Avogadro’s number • Not useful for measuring everyday items

3. How Much is a Mole? • 6.02 X 1023 Watermelon Seeds: Would be found inside a melon slightly larger than the moon. • 6.02 X 1023 Donut Holes: Would cover the earth and be 5 miles (8 km) deep. • 6.02 X 1023  Pennies: Would make at least 7 stacks that would reach the moon. • 6.02 X 1023  Grains of Sand: Would be more than all of the sand on Miami Beach. • 6.02 X 1023  Blood Cells: Would be more than the total number of blood cells found in every human on earth. • 6.02 X 1023  C02 Molecules: Would be found in 1 Mole BalloonTM at STP.

4. Why did scientists need a mole? • They knew that equal volumes of gases at standard temp and pressure (STP) had an equal number of particles • They knew that 32 g of O2 and 2 g of H2 had a volume of 22.4 L. • They determined that that number of particles was 6.02 x 1023, or one mole

5. What is the difference between atomic mass and formula mass? • Atomic mass is expressed in atomic mass units • Atomic mass unit: (amu) one twelfth the mass of the carbon 12-isotope • Most elements do not have whole number mass • the atomic mass is an average of the masses of all of the isotopes of that element • the actual mass of a proton and neutron is not equal to exactly 1 amu • Formula mass: the sum of the atomic masses of all of the atoms in a compound in amus

6. How do I calculate formula mass? • It is found by summing the atomic masses of all of the atoms in a compound • The mass unit is amus • Example: H2SO4 has 2 H’s, 1 S, and 4 O’s 2 (1.01 amu) + (32.07 amu) + 4(16.00 amu) = 98.09 amu So, the formula mass of H2SO4 is 98.09 amu

7. What is molar mass? • Mass of 1 mole of a compound • Measured in grams • It is the mass in grams of one mole of a given substance • It is equal to the average atomic mass of that element, written in grams • It depends on the masses of the elements that make up the substance • It is calculated exactly like formula mass, but with different units (g instead of amu)

8. How to find molar mass • Find the molar mass of Na2SO4 • Find the molar mass of MgSO4· 7H2O

9. How do I convert from moles to mass? • You must use molar mass • How many moles of water are in 18.01 g of water? • What is the mass of 15.2 moles of CO2?

10. What is Avogadro’s Number? • 6.02 x 1023: the number of representative particles (atoms, molecules, formula units) in exactly one mole of a substance • Atoms – The representative particle in an element • Molecules – The representative particle in a molecule of liquid • Formula Units – The representative particle in a compound • Mole: the fundamental SI unit used to measure the amount of a substance

11. How can I convert moles to number of particles? • Avogadro’s Number is used as a factor in converting from a given number of moles to the equivalent number of atoms. • To convert from moles to number of particles, you must use dimensional analysis.

12. How do I convert moles to particles? • Remember Avogadro’s Number • 6.02 x 1023 particles 1 mole • So, # moles x 6.02 x 1023 particles = 1 mole # particles

13. Sample Problems A) # atoms in 2.50 mol Zn B) # molecules in 11.5 mol H2O

14. How do I convert moles to volume? • Molar volume: the volume of 1 mole of a gas at standard temperature and pressure (0°C and 1 atmosphere; abbreviated STP) • Gases change volume with changes in temperature, pressure, or both; so, temp and press must be specified when giving the volume of a gas • 1 mole of gas = 22.4 L • This is true ONLY at STP

15. To convert moles to volume • How many moles will be in 44.8 L of O2? • What is the volume of 0.725 moles of NH3?

16. How do I combine multiple conversions? • You can combine the above processes together to simplify calculations