Ch 11 The Mole

11.1 Measuring matter

VocabularyReview

molecule - two or more atoms that covalently bond together to form a unitNew

moleAvogadro’s number

Main Idea - Chemists use the mole to count atoms, molecules, ions, and formula units.

NOTE – YOU WILL NEED A SCIENTIFIC CALCULATOR FOR THIS CHAPTER!

How do we measure items?

You can measure ____________ ,________________,or ________________,

You can count ________________.

We measure mass in________________.

We measure distance in _________________.

We measure volume in________________.

We count pieces in _________________.

Counting Particles• Chemists need a convenient method for accurately counting the number of atoms, molecules,

or formula units of a substance.

• The _____________is the SI base unit used to measure the amount of a substance.

Moles (is abbreviated: mol) It is an __________________, defined as the number of carbon atoms in exactly 12 grams of

carbon-12.

1 mole = _______________________ of the representative particles.

Treat it like a very large dozen!

6.022 x 1023 is called ________________________________________.

Similar Words for an amount– Pair: 1 pair of shoelaces = ____ shoelaces

– Dozen: 1 dozen oranges = ____ oranges

– Case: 1 case of Dr. Pepper = ____ cans Dr. Pepper

– Gross: 1 gross of pencils = ______ pencils

– Ream: 1 ream of paper = _______sheets of paper

What are Representative Particles? The___________________ pieces of a substance:

1) For a molecular compound: it is the_____________________.

2) For an ionic compound: it is the formula_____________ (made of ions).

3) For an element: it is the __________.

• Remember the 7 diatomic elements? (made of molecules)

Types of questions• How many oxygen atoms in the following?

CaCO3

Al2(SO4)3

• How many ions in the following?

CaCl2

NaOH

Al2(SO4)3

Converting Between Moles and Particles• ____________________________________ must be used.

Moles to particles

Example:Find the number of molecules in 3.50 mol of sucrose.

Always start with what you are given!

Particles to moles– Use the inverse of Avogadro’s number as the conversion factor.

Example:Find the number of moles in 2.11 x 1024 molecules of sucrose.

Practice problems (round to 3 sig. figs.) How many molecules of CO2 are in 4.56 moles of CO2?

How many moles of water is 5.87 x 1022 molecules?

How many atoms of carbon are in 1.23 moles of C6H12O6?

How many moles is 7.78 x 1024 formula units of MgCl2?

11.2 Mass and the Mole

VocabularyReviewconversion factor: a ratio of equivalent values used to express the same quantity in different unitsNewmolar massMain Idea - A mole always contains the same number of particles; however, moles of different substances have different masses.

The Mass of a Mole• 1 mol of copper and 1 mol of carbon have _______________________________.

o One copper atom has a different mass than 1 carbon atom. Remember relative atomic mass?

- The ___________was one twelfth the mass of a carbon-12 atom. Since the mole is the number of atoms in 12 grams of carbon-12,

- the _______________________________________________________is also the mass of _______________ of those atoms in grams.

• __________________ (MM) is the ______________________________________ of any pure substance.

• Also called _________________________ (FW)

Equals the_____________ of 1 mole of an element in grams (from periodic table) 12.011 grams of C has the same _______________________________ as

o ___________ grams of H o ___________ grams of iron.

We can write this as: ____________________________ We can count things by weighing them.

Using Molar Mass• Moles to mass

• Convert mass to moles with the inverse molar mass conversion factor.

Examples How much would 2.34 moles of carbon weigh?

How many moles of magnesium is 24.31 g of Mg?

How many atoms of lithium is 1.00 g of Li?

How much would 3.45 x 1022 atoms of U weigh?

Using Molar Mass (cont.)• This figure shows the steps to complete conversions between mass and atoms.

11.3 Moles of compounds

VocabularyReview representative particle: an atom, molecule, formula unit, or ionMain Idea -The molar mass of a compound can be calculated from its chemical formula and can be used to convert from mass to moles of that compound.

Chemical Formulas and the Mole• Chemical formulas indicate the numbers and types of atoms contained in one unit of the

compound.• One mole of CCl2F2 contains _______________ of C atoms, __________________ of Cl atoms,

and two moles of F atoms.

The Molar Mass of Compounds• The molar mass of a compound equals the molar mass of each element, multiplied by the moles

of that element in the chemical formula, added together.

• The molar mass of a compound demonstrates the law of conservation of mass.

in 1 mole of H2O molecules there are ________moles of H atoms and_______ mole of O atoms

(think of a compound as a molar ratio)

To find the mass of one mole of a compound

o _____________________ the number of__________ of the elements present

o __________________ the number times their ____________ (from the periodic table)

o ______________ them up for the total mass

Calculating Molar Mass Example

Calculate the molar mass of magnesium carbonate, MgCO3.

More Examples – Molar mass of compoundsCalculate the molar mass of the following and tell what type of substance it is:

Na2S

N2O4

C

Ca(NO3)2

C6H12O6

(NH4)3PO4

Moles to Mass Conversion for Compounds• For elements, the conversion factor is the molar mass of the elements.

• The procedure is the same for compounds, except that you must ___________________________________________________ of the compound.

Mass to Moles Conversion for Compounds• The conversion factor is the inverse of the molar mass of the compound.

For exampleHow many moles is 5.69 g of NaOH?

Mass to Particles Conversion for Compounds• Convert mass to moles of compound with the inverse of molar mass.• Convert moles to particles with Avogadro’s number.• This figure summarizes the conversions between mass, moles, and particles.

11.4 Empirical and Molecular formulas

VocabularyReview

percent by mass: the ratio of the mass of each element to the total mass of the compound expressed as a percent

New percent compositionempirical formulamolecular formula

Main Idea - A molecular formula of a compound is a whole-number multiple of its empirical formula.

Percent Composition• The ________________________________ of any element in a compound can be found by

dividing the mass of the element by the mass of the compound and multiplying by 100.

• The percent by mass of each element in a compound is the _____________________________ of a compound.

• Percent composition of a compound can also be determined from its chemical formula.

Like all percent problems:

1. Find the mass of each of the _____________________.

2. Next, ___________________________________of the compound; then x ___________

ExampleCalculate the percent composition of a compound that is made of 29.0 grams of Ag with 4.30 grams of S(Assume you have one mol of substance)

More Examples Calculate the percent composition of C2H4?

How about Aluminum carbonate?

Empirical Formula• The ___________________________ for a compound is the

_______________________________________ of the elements.

• To calculate the empirical formula from percent by mass:

1) Assume you have 100.00 g of the compound.

2) Convert the mass of each element to moles.

• The empirical formula may or may not be the same as the molecular formula.

Molecular formula of hydrogen peroxide = H2O2

Empirical formula of hydrogen peroxide = HO

Molecular Formula• The ________________________________ specifies the _______________________________

of each element in one molecule or formula unit of the substance.

• Molecular formula is always a _________________________________ of the empirical formula.

11.5 Formulas of hydrates

VocabularyReview

crystal lattice: a three-dimensional geometric arrangement of particles New

hydrate

Main Idea -Hydrates are solid ionic compounds in which water molecules are trapped.

Naming Hydrates• A __________________ is a compound that has a

specific number of water molecules bound to its atoms.

• The number of water molecules associated with each formula unit of the compoundis written following a dot.

Example

Analyzing Hydrates• When heated, water molecules are released from a hydrate leaving an

______________________________________.

• To determine ________________________________, find the number of moles of water associated with 1 mole of hydrate.1. ______________hydrate.2. _____________ to drive off the water.3. Weigh the anhydrous compound.4. _____________ and convert the difference to moles.5. The _____________________________________ to moles of anhydrous compound is the

____________________________________ in the hydrate.

Use of Hydrates• Anhydrous forms of hydrates are often used to __________________________, particularly

during shipment of electronic and optical equipment.

• In chemistry labs, anhydrous forms of hydrates are used to remove moisture from the air and keep other substances dry.