Chapter 7 Moles

What is a Representative Particle The smallest unit into which a substance can be broken down without changing the composition of the substance. Atoms, molecules, and formula units

What is a mole? A mole is a measurement Other measurements include: –Couple, dozen, ream, gross, etc.

What is a mole (mol)? A HUGE NUMBER! –602,000,000,000,000,000,000,000 Avogadro's Number Memorize this number! 1 mole = 6.02 x representative particles

Formulas Moles x 6.02 x = particles Particle ÷ 6.02 x = moles Moles x molar mass = grams Grams ÷ molar mass = moles Moles x 22.4 = liters Liters ÷ 22.4 = moles

Mole Conversions—Moles to Particles If you know the moles of a substance, you can calculate the number of particles in it. Use Avogadro’s number to calculate Moles is the crossroad to all conversions

Mole Conversions—Moles to Particles Ex. How many water molecules are there in 2.00 moles of water? 2 moles H 2 0 x 6.02 x molecules 1.20 X H 2 O molecules

Problems How many moles of magnesium is 1.25 x atoms of magnesium? 1.25 x atoms Mg ( 6.02 X atoms Mg) 2.08 X mol of Mg or mol Mg

How many molecules are in 2.12 mols of propane (C 3 H 8 )? 2.12 mol C 3 H 8 x 6.02 x molecules 1.28 x molecules of C 3 H 8

Think about this… If you had a mole of water, would you be able to swim in it?

How can this happen? One mole of zinc is 65.4 grams One mole of calcium is 40.1 grams One mole of magnesium is 24.3 grams Different densities

Atomic Mass Protons and neutrons each have a mass of 1 atomic mass unit (amu) One mole of atomic mass units equals 1 gram. Carbon-12 has 12 amu –One mole of carbon is 12 grams

The mass of a mole of an element such as carbon is called the gram atomic mass (gam) The mass of a mole of a covalent compound such as water is called the gram molecular mass (gmm) The mass of a mole of an ionic compound such as NaCl is called the gram formula mass (gfm) All three of these can simply be called the MOLAR MASS.

Finding the Molar Mass Find the molar mass of SO 3 Add the atomic masses of the atoms that make the molecule. Round to the tenth. 1 S = O: (3 x 16.0 amu) = amu = 80.1 grams/mol

Mole Conversions—Mass to Moles If you know the mass of a substance, you can calculate the number of moles. Ex.: You have 11.2 g of NaCl. How many moles is that?

First: Calculate the molar mass of NaCl. Na = 23.0 g/mol Cl = 35.5 g/mol NaCl = = 58.5 g/mol This means 1 mol of NaCl = 58.5 g NaCl

Use the molar mass to calculate the number of moles in 11.2 g of NaCl. Use the formula g NaCl 58.5 g NaCl Answer: moles NaCl

Mole Conversions—Moles to Mass If you know the number of moles, you can calculate the mass. Ex. How many grams are in 2.50 mol of NaCl?

Use the molar mass formula to convert to grams mol NaCl x 58.5 g NaCl Answer: 146 grams of NaCl

Practice Problems How many moles are there in 1.50 x molecules NH 3 ? Calculate the molar mass: N 2 O 3 ? How many moles are in 15.5 g SiO 2 ? What is the mass of 14.4 mol F 2 ?

Practice Problems How many moles are there in 1.50 x molecules NH 3 ? Answer: mols NH 3 Calculate the molar mass: N 2 O 3 ? Answer: 76.0 grams/mol How many moles are in 15.5 g SiO 2 ? Answer: mols SiO 2 What is the mass of 14.4 mol F 2 ? Answer: 547 g F 2

Volume of a Mole of Gas Volumes of gases vary with changes in their temperatures and pressures In experiments, gas volumes are measured at STP (standard temperature and pressure) Standard temperature is 0° C or 273 K Standard pressure is 1 atm or kPa One mole of all gases at STP have a volume of 22.4 L

Practice Problem What is the volume, at STP, of a balloon containing 25.0 grams of carbon dioxide? 25.0 g CO 2 = 0.568… mol CO 2 x 22.4 L 44.0 g/mol 12.7 L CO 2

Balanced STP Coefficients are moles and molecules Moles x molar mass = grams Moles x 22.4 = L

CH 4 + 2O 2  CO 2 + 2H 2 How many mole of H 2 O? 2 mol How many molecules of H 2 O? 2 molecules How many liters of O 2 ? 2 x 22.4 = 44.8 L How many grams of product? = 80.0 g

Percent Composition The percent by mass of each element in a compound % composition = mass of element x 100 mass of compound

Practice Problem An 8.20 g piece of magnesium combines with oxygen to form g of magnesium oxide. What is the percent composition of this compound? % Mg = 8.20 g Mg ÷ g MgO x % Magnesium g MgO – 8.20 g Mg = 5.40 g % O = 5.40 g O ÷ g MgO x % Oxygen

Practice Problem What is the percent composition of NaCl? Na is 23.0 g/mol + Cl is 35.5 g/mol = NaCl at 58.5 g/mol % Na = 23.0 g/mol ÷ 58.5 g/mol x % sodium % Cl = 35.5 g/mol ÷ 58.5 g/mol x % chlorine

Problem Continued How much sodium is there in 454 g NaCl? 39.3 % ÷ 100 = g NaCl x = = 178 g Na

Empirical Formula Shows the lowest whole-number ratio of the atoms of the elements in a compound What is the empirical formula of C 8 H 18 ? C 4 H 9 What is the empirical formula of H 2 O? H 2 O

Molecular Formula Shows the actual number and kinds of atoms present in a molecule of a compound The empirical formula of a compound is C 2 H 5. The molar mass is 58.0 g/mol. What is the molecular formula?

Molecular Formula Continued C = 12.0 g/mol and H = 1.0 g/mol C 2 H 5 = 24.0 g/mol g/mol = 29.0 g/mol 58.0 g/mol ÷ 29.0 g/mol = 2 C 2 H 5 x 2 = C 4 H 10

Formula from Percent What is the formula for a compound of iron and chlorine that is 34.4 % iron and 65.6 % chlorine by weight? Assume 100 grams of compound % becomes 34.4 g of Fe and 65.6% becomes 65.6 g of Cl Convert to moles g ÷ 55.8 g/mol = mols

Continued 65.6 g ÷ 35.5 g/mol = mols Find the mole ratio (divide each mole value by the smallest mole value) mols ÷ mols = mols ÷ mols = 3.0 The mole ratios are the subscripts. FeCl 3