Transcript Ch 11: The Mole
Ch 11: The Mole
Section 11.1
• Dozen= • 12 • Ream= • 500 • Pair= • 2 • Gross= • 144
Measuring Matter
• What is a mole?
• It is the SI base unit used to measure the amount of a substance • Abbreviated
mol
• Represents particles • Is also called Avogadro ’ s number 6.02 x 10 23 (3 significant figures)
• • Remember conversion factors? • 12 roses = 1 dozen So, 3.5 dozen= ? Roses = 42 Well, 6.02 x 10 23 atoms (or any representative paticles) = 1 mol
• Review Scientific Notation • Review Rounding
• Example: • 3.50 mol sucrose has how many molecules?
• Work practice problems 1-3 • Example: • How many moles are in 3.58 X 10 20 atoms of Ca?
• Work practice problems 4-7
closure
• • •
How is a mole similar to a dozen?
What is the relationship between avagadro
’
s number & one mole?
Why do chemists use moles?
• • **worksheet: The mole & Avogadro ’ s number
STOP
Section 11.2 Mass & the Mole
• Different particles (atoms) have different masses. • Remember atomic mass. – Each element has its own specific mass.
–
Therefore each compound has its own specific mass.
• Molar mass (g/mol)-mass in grams of any pure substance • The molar mass of any element is numerically equal to its atomic mass.
• Thus…1 mol Mn = 54.94 g/mol Mn = 6.02 x 1023 atoms Mn
• Example: • 1 mol Zn = • 1 mol O 2 = 65.4 g/mol 32.0 g/mol
• • • • Practice 3 mol Zinc = 196 g/mol Zn 1 mol H 2 O = 18.0g/mol H 2 O 1 mol sulfuric acid = 98.1 g/mol H 2 SO 4
Mass
Mole conversions
• Example: • Calculate the mass in grams of 0.0450 mol Cr.
• Work Practice problems 1-4
• Hydrate: CuSO 4 ·5H 2 O 4) Calculate the mass in grams of 2.45 mol of CaCl 2
·
2H 2 O
Mole
Mass conversions
• Example: • Determine the number of moles for 25.5 g Ag. (mass mol) • Work practice problems 5-7.
**worksheet: moles & mass
Mass
Atom Conversion
• Example: – How many atoms of gold (Au) are in a pure nugget having the mass of 25.0g?
– Practice problems 1-5
Atom
Mass Conversion
• Example • A party balloon contains 5.50 x 10 22 atoms of helium (He) gas. What is the mass in grams of the helium?
• Practice problems 6-10.
Mole
Mole
Example • According to the following balanced equation, how many moles of O 2 is produced from 3.00 moles of CuO?
2CuO 2Cu + O 2 Practice problems 1 & 2.
Section 11.4 Empirical & Molecular Formula
• Percent Composition is the percent by mass of each element in a compound.
Example: • If we had 100 g of a sample of some new compound contains 55g of element X & 45 g of element Y. What is the % of element X & Y?
• If we already know the _chemical formula for a compound, you can calculate its percent composition.
• • % by mass= Mass of element in 1 mol of compound Molar mass of compound X 100
• Ex. Determine the percent composition of H2O.
• (If you had 350. g of water, then how much is oxygen?) • Practice problems 1-3.
• Empirical Formula is the smallest whole number ratio of the elements.
• Calculating Empirical formula from percent composition: • Directions: • The percent should be assumed to be 100 g & converted to moles. Then we figure out the mole ratio by dividing each by the smallest mole.
POEM:
1. Percent to Mass 2. Mass to Mole 3. Divide by small 4. Multiply til whole.
• Example 1 • The percent composition of an oxide of sulfur is 40.05% S & 59.95% O.
• Example 2 • Determine the empirical formula for methyl acetate which has the following chemical analysis:48.64% C, 8.16% H, & 43.20% O.
• Practice Problems
•
**worksheet: determining empirical formulas