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