Section 10-1 Counting Particles Chemists need a convenient method for accurately counting the number...
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Transcript of Section 10-1 Counting Particles Chemists need a convenient method for accurately counting the number...
Section 10-1
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.
Section 10-1
Converting Between Moles and Particles
• Conversion factors must be used.
• Moles to particles
Section 10-1
Converting Between Moles and Particles (cont.)
• Particles to moles
• Use the inverse of Avogadro’s number as the conversion factor.
End of Section 10-1
Section 10-2
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.
• 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.
Section 10-2
Using Molar Mass
• Moles to mass
• Convert mass to moles with the inverse molar mass conversion factor.
• Convert moles to atoms with Avogadro’s number as the conversion factor.
End of Section 10-2
Section 10-3
Section 10.3 Moles of Compounds (cont.)
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 indicate the numbers and types of atoms contained in one unit of the compound.
Section 10-3
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.
Section 10-3
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.
• The conversion factor is the inverse of the molar mass of the compound.
Section 10-3
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.
End of Section 10-3
Section 10-4
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.
Section 10-4
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.
Section 10-4
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
Section 10-4
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.
Section 10-4
Molecular Formula (cont.)
End of Section 10-4
Section 10-5
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
Section 10-5
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.
Section 10-5
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.
Section 10-5
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.