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 10 23 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.

Section 10.1 Assessment What does the mole measure? A. mass of a substance B. amount of a substance C. volume of a gas A. A D. density of a gas B. B C. C 0% 0% 0% 0% D. D A B C D

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. A. A B. B. B C. C C. 1 particle 6.02 10 23 0% 0% 0% 0% D. D A B C D D. 1 mol 6.02 10 23 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.

Section 10.2 Assessment The mass in grams of 1 mol of any pure substance is: A. molar mass B. Avogadro’s number A. A C. atomic mass B. B D. 1 g/mol C. C 0% 0% 0% 0% D. D A B C D

Section 10.2 Assessment Molar mass is used to convert what? A. mass to moles B. moles to mass C. atomic weight A. A D. particles B. B C. C 0% 0% 0% 0% D. D A B C D

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.

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 A. A C. 4.00 B. B D. 5.00 C. C 0% 0% 0% 0% D. D A B C D

Section 10.3 Assessment How many particles of Mg are in 10 moles of MgBr 2 ? A. 6.02 10 23 B. 6.02 10 24 A. A C. 1.20 10 24 B. B D. 1.20 10 25 C. C 0% 0% 0% 0% D. D A B C D

Section 10.4 Empirical and Molecular Formulas • Explain what is meant by percent by mass: the the percent composition ratio of the mass of each of a compound. element to the total mass of the compound • Determine the expressed as a percent empirical and molecular formulas for a compound from mass percent composition percent and actual mass data. empirical formula molecular formula 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 = H 2 O 2 Empirical formula of hydrogen peroxide = HO

Molecular Formula • The molecular formula specifies the actual number of atoms of each element in one molecule or formula unit of the substance. • Molecular formula is always a whole-number multiple of the empirical formula.

Molecular Formula (cont.)

Section 10.4 Assessment What is the empirical formula for the compound C 6 H 12 O 6 ? A. CHO B. C 2 H 3 O 2 A. A C. CH 2 O B. B D. CH 3 O C. C 0% 0% 0% 0% D. D A B C D

Section 10.4 Assessment Which is the empirical formula for hydrogen peroxide? A. H 2 O 2 B. H 2 O A. A C. HO B. B D. none of the above C. C 0% 0% 0% 0% D. D A B C D

Section 10.5 Formulas of Hydrates • Explain what a hydrate crystal lattice: a three- is and relate the name of dimensional geometric the hydrate to its arrangement of particles composition. • Determine the formula of a hydrate from hydrate 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 = Na 2 CO 3 • 10H 2 O

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: AlPO 4 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

Section 10.5 Assessment Heating a hydrate causes what to happen? A. Water is driven from the hydrate. B. The hydrate melts. A. A C. The hydrate conducts electricity. B. B D. There is no change in the C. C hydrate. 0% 0% 0% 0% D. D A B C D

Section 10.5 Assessment A hydrate that has been heated and the water driven off is called: A. dehydrated compound B. antihydrated compound A. A C. anhydrous compound B. B D. hydrous compound C. C 0% 0% 0% 0% D. D A B C D

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