Counting Particles Chemists need a convenient method for accurately - - PowerPoint PPT Presentation

Counting Particles

• Chemists need a convenient method for

accurately counting the number of atoms, molecules, or formula units of a substance.

• The mole is the SI base unit used to measure

the amount of a substance.

• 1 mole is the amount of atoms in 12 g of pure

carbon-12, or 6.02 1023 atoms.

• The number is called Avogadro’s number.

Converting Between Moles and Particles

• Conversion factors must be used.
• Moles to particles

Number of molecules in 3.50 mol of sucrose

Converting Between Moles and Particles (cont.)

• Particles to moles
• Use the inverse of Avogadro’s number as the

conversion factor.

• A. A
• B. B
• C. C
• D. D

A B C D

0% 0% 0% 0%

Section 10.1 Assessment What does the mole measure?

• A. mass of a substance
• B. amount of a substance
• C. volume of a gas
• D. density of a gas

• A. A
• B. B
• C. C
• D. D

A B C D

0% 0% 0% 0%

Section 10.1 Assessment What is the conversion factor for determining the number of moles of a substance from a known number of particles? A. B.

• C. 1 particle 6.02 1023
• D. 1 mol 6.02 1023

particles

The Mass of a Mole

• 1 mol of copper and 1 mol of carbon have

different masses.

• One copper atom has a different mass than 1

carbon atom.

The Mass of a Mole (cont.)

• Molar mass is the mass in grams of one

mole of any pure substance.

• The molar mass of any element is

numerically equivalent to its atomic mass and has the units g/mol.

Using Molar Mass

• Moles to mass

3.00 moles of copper has a mass of 191 g.

Using Molar Mass (cont.)

• Convert mass to moles with the inverse

molar mass conversion factor.

• Convert moles to atoms with Avogadro’s

number as the conversion factor.

Using Molar Mass (cont.)

• This figure shows the steps to complete

conversions between mass and atoms.

• A. A
• B. B
• C. C
• D. D

A B C D

0% 0% 0% 0%

Section 10.2 Assessment The mass in grams of 1 mol of any pure substance is:

• A. molar mass
• B. Avogadro’s number
• C. atomic mass
• D. 1 g/mol

• A. A
• B. B
• C. C
• D. D

Section 10.2 Assessment

A B C D

0% 0% 0% 0%

Molar mass is used to convert what?

• A. mass to moles
• B. moles to mass
• C. atomic weight
• D. particles

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.

Converting Moles of a Compound to Mass

• For elements, the conversion factor is the

molar mass of the compound.

• The procedure is the same for compounds,

except that you must first calculate the molar mass of the compound.

Converting the Mass of a Compound to Moles

• The conversion factor is the inverse of the

molar mass of the compound.

Converting the Mass of a Compound to Number of Particles

• Convert mass to moles of compound with

the inverse of molar mass.

• Convert moles to particles with Avogadro’s

number.

Converting the Mass of a Compound to Number of Particles (cont.)

• This figure summarizes the conversions

between mass, moles, and particles.

• A. A
• B. B
• C. C
• D. D

A B C D

0% 0% 0% 0%

Section 10.3 Assessment How many moles of OH— ions are in 2.50 moles of Ca(OH)2?

• A. 2.00
• B. 2.50
• C. 4.00
• D. 5.00

• A. A
• B. B
• C. C
• D. D

Section 10.3 Assessment

A B C D

0% 0% 0% 0%

How many particles of Mg are in 10 moles

• f MgBr2?
• A. 6.02 1023
• B. 6.02 1024
• C. 1.20 1024
• D. 1.20 1025

Section 10.4 Empirical and Molecular Formulas

• Explain what is meant by

the percent composition

• f a compound.

percent by mass: the ratio of the mass of each element to the total mass of the compound expressed as a percent percent composition empirical formula molecular formula

• Determine the

empirical and molecular formulas for a compound from mass percent and actual mass data. A molecular formula of a compound is a whole-number multiple of its empirical formula.

Percent Composition

• The percent by mass 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.

Percent Composition (cont.)

• The percent by mass of each element in a

compound is the percent composition of a compound.

• Percent composition of a compound can also

be determined from its chemical formula.

Empirical Formula

• The empirical formula for a compound is

the smallest whole-number mole ratio of the elements.

• You can calculate the empirical formula from

percent by mass by assuming you have 100.00 g of the compound. Then, 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 molecular formula specifies the

actual number of atoms of each element in

• ne molecule or formula unit of the

substance.

• Molecular formula is always a whole-number

multiple of the empirical formula.

Molecular Formula (cont.)

• A. A
• B. B
• C. C
• D. D

A B C D

0% 0% 0% 0%

Section 10.4 Assessment What is the empirical formula for the compound C6H12O6?

• A. CHO
• B. C2H3O2
• C. CH2O
• D. CH3O

• A. A
• B. B
• C. C
• D. D

Section 10.4 Assessment

A B C D

0% 0% 0% 0%

Which is the empirical formula for hydrogen peroxide?

• A. H2O2
• B. H2O
• C. HO
• D. none of the above

Section 10.5 Formulas of Hydrates

• Explain what a hydrate

is and relate the name of the hydrate to its composition. crystal lattice: a three- dimensional geometric arrangement of particles hydrate

• Determine the formula
• f a hydrate from

laboratory data. Hydrates are solid ionic compounds in which water molecules are trapped.

Naming Hydrates

• A hydrate 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 compound is written following a dot.

• Sodium carbonate decahydrate =

Na2CO3 • 10H2O

Naming Hydrates (cont.)

Analyzing a Hydrate

• When heated, water molecules are

released from a hydrate leaving an anhydrous compound.

• To determine the formula of a hydrate, find

the number of moles of water associated with 1 mole of hydrate.

Analyzing a Hydrate (cont.)

• Weigh hydrate.
• Heat to drive off the water.
• Weigh the anhydrous compound.
• Subtract and convert the difference to moles.
• The ratio of moles of water to moles of

anhydrous compound is the coefficient for water in the hydrate.

Use of Hydrates

• Anhydrous forms of hydrates are often

used to absorb water, 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.

• Study for Test:
• How moles of different substances

compare: same # of particles different masses

• Definition of mole.
• Avogadro’s number
• Molar mass compared to molecular and

atomic mass

• Number of moles of atoms in a mole of a

compound: Ex: AlPO4 has 6 moles of atoms, one Al, one P, four O.

• How to determine molar mass.
• How to determine percent composition.
• How to do molar conversions.
• MAKE SURE YOU HAVE A

CALCULATOR

• A. A
• B. B
• C. C
• D. D

A B C D

0% 0% 0% 0%

Section 10.5 Assessment Heating a hydrate causes what to happen?

• A. Water is driven from the hydrate.
• B. The hydrate melts.
• C. The hydrate conducts

electricity.

• D. There is no change in the

hydrate.

• A. A
• B. B
• C. C
• D. D

Section 10.5 Assessment

A B C D

0% 0% 0% 0%

A hydrate that has been heated and the water driven off is called:

• A. dehydrated compound
• B. antihydrated compound
• C. anhydrous compound
• D. hydrous compound

This slide is intentionally blank.