Mass Relationships in Chemical Reactions Chapter 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

By definition: 1 atom 12 C “weighs” ___ amu On this scale 1 H = amu 16 O = amu __________ __________ is the mass of an atom in atomic mass units (amu) Micro World atoms & molecules Macro World grams 3.1

Natural lithium is: 7.42% 6 Li (6.015 amu) 92.58% 7 Li (7.016 amu) 7.42 x x = _________ amu 3.1 ____________ atomic mass of lithium:

Average atomic mass (6.941)

The __________ (______) is the amount of a substance that contains as many elementary entities as there are atoms in exactly grams of 12 C mol = N A = x Avogadro’s number (N A )

_____ _____ is the mass of 1 mole of in grams eggs shoes marbles atoms 1 mole 12 C atoms = x atoms = g 1 12 C atom = _______ 1 mole 12 C atoms = ___________ g 12 C 1 mole lithium atoms = ___________ g of Li For any element atomic mass (____) = molar mass (_____) 3.2

One Mole of: C S Cu Fe Hg 3.2

1 amu = 1.66 x g or 1 g = x amu 1 12 C atom amu x g x C atoms = 1.66 x g 1 amu 3.2 M = molar mass in g/mol N A = Avogadro’s number

x x atoms K 1 mol K = Do You Understand Molar Mass? How many atoms are in g of potassium (K) ? 1 mol K = _________ g K 1 mol K = ______________ atoms K g K 1 mol K g K x ______________ atoms K 3.2

_______ _______ (or molecular weight) is the sum of the atomic masses (in amu) in a molecule. SO 2 1S32.07 amu 2O+ 2 x amu SO amu For any molecule molecular mass (____) = molar mass (_____) 1 ____________ SO 2 = amu 1 __________ SO 2 = g SO 2 3.3

Do You Understand Molecular Mass? How many H atoms are in 72.5 g of C 3 H 8 O ? 1 mol C 3 H 8 O = (3 x 12) + (8 x 1) + 16 = ___ g C 3 H 8 O 1 mol H = ______________ atoms H ________________ atoms H mol C 3 H 8 O molecules = ___ mol H atoms 72.5 g C 3 H 8 O 1 mol C 3 H 8 O 60 g C 3 H 8 O x 8 mol H atoms 1 mol C 3 H 8 O x x H atoms 1 mol H atoms x =

___________ _______ is the sum of the atomic masses (in amu) in a formula unit of an ionic compound. 1Na22.99 amu 1Cl amu NaCl amu For any __________ compound formula mass (amu) = molar mass (grams) 1 formula unit NaCl = amu 1 mole NaCl = g NaCl 3.3 NaCl

Do You Understand Formula Mass? What is the formula mass of Ca 3 (PO 4 ) 2 ? formula unit of Ca 3 (PO 4 ) 2 3 Ca 3 x _____ 2 P2 x _____ 8 O + 8 x _____ ______ amu

KE = 1/2 x m x v 2 v = (2 x KE/m) 1/2 F = q x v x B 3.4 Light Heavy

___________ __________ of an element in a compound = n x molar mass of element molar mass of compound x 100% n is the number of moles of the element in _______ of the compound C2H6OC2H6O %C = 2 x (12.01 g) g x 100% = 52.14%H = 6 x (1.008 g) g x 100% = 13.13%O = 1 x (16.00 g) g x 100% = 34.73% 52.14% % % = 100.0% 3.5

Percent Composition and Empirical Formulas Determine the empirical formula of a compound that has the following percent composition by mass: K 24.75, Mn 34.77, O percent. n K = g K x = mol K 1 mol K g K n Mn = g Mn x = mol Mn 1 mol Mn g Mn n O = g O x = mol O 1 mol O g O

3.5 Percent Composition and Empirical Formulas K : ~ ~ Mn : = 1.0 O : ~ ~ n K = , n Mn = , n O = KMnO 4

3.6 g CO 2 mol CO 2 mol Cg C g H 2 O mol H 2 Omol Hg H g of O = g of sample – (g of C + g of H) Burn 11.5 g ethanol Collect 22.0 g CO 2 and 13.5 g H 2 O 6.0 g C = 0.5 mol C 1.5 g H = 1.5 mol H 4.0 g O = 0.25 mol O Empirical formula C 0.5 H 1.5 O 0.25 Divide by smallest subscript (0.25) Empirical formula C 2 H 6 O

3.7 3 ways of representing the reaction of H 2 with O 2 to form H 2 O A process in which one or more substances is changed into one or more new substances is a ___________ ___________ A ___________ ___________ uses chemical symbols to show what happens during a chemical reaction ___________

How to “Read” Chemical Equations 2 Mg + O 2 2 MgO 2 atoms Mg + 1 molecule O 2 makes 2 formula units MgO 2 moles Mg + 1 mole O 2 makes 2 moles MgO 48.6 grams Mg grams O 2 makes 80.6 g MgO IS NOT 2 grams Mg + 1 gram O 2 makes 2 g MgO 3.7

Balancing Chemical Equations 1.Write the correct formula(s) for the reactants on the left side and the correct formula(s) for the product(s) on the right side of the equation. Ethane reacts with oxygen to form carbon dioxide and water C 2 H 6 + O 2 CO 2 + H 2 O 2.Change the numbers in front of the formulas ( ___________ ) to make the number of atoms of each element the same on both sides of the equation. Do not change the ___________ C 2 H 6 NOT C 4 H 12

Balancing Chemical Equations 3.Start by balancing those elements that appear in only one reactant and one product. C 2 H 6 + O 2 CO 2 + H 2 O 3.7 start with C or H but not O 2 carbon on left 1 carbon on right multiply CO 2 by 2 C 2 H 6 + O 2 2CO 2 + H 2 O 6 hydrogen on left 2 hydrogen on right multiply H 2 O by 3 C 2 H 6 + O 2 2CO 2 + 3H 2 O

Balancing Chemical Equations 4.Balance those elements that appear in two or more reactants or products oxygen on left 4 oxygen (2x2) C 2 H 6 + O 2 2CO 2 + 3H 2 O + 3 oxygen (3x1) multiply O 2 by 7 2 = 7 oxygen on right C 2 H 6 + O 2 2CO 2 + 3H 2 O 7 2 remove fraction multiply both sides by 2 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O

Balancing Chemical Equations 5.Check to make sure that you have the same number of each type of atom on both sides of the equation C 2 H 6 + 7O 2 4CO 2 + 6H 2 O ReactantsProducts 4 C 12 H 14 O 4 C 12 H 14 O 4 C (2 x 2)4 C 12 H (2 x 6)12 H (6 x 2) 14 O (7 x 2)14 O (4 x 2 + 6)

1.Write ___________ chemical equation 2.Convert quantities of known substances into moles 3.Use coefficients in balanced equation to calculate the number of moles of the sought quantity 4.Convert moles of sought quantity into desired units Amounts of Reactants and Products 3.8

Methanol burns in air according to the equation 2CH 3 OH + 3O 2 2CO 2 + 4H 2 O If 209 g of methanol are used up in the combustion, what mass of water is produced? grams CH 3 OHmoles CH 3 OHmoles H 2 Ograms H 2 O molar mass CH 3 OH coefficients chemical equation molar mass H 2 O 209 g CH 3 OH 1 mol CH 3 OH 32.0 g CH 3 OH x 4 mol H 2 O 2 mol CH 3 OH x 18.0 g H 2 O 1 mol H 2 O x = _________ g H 2 O 3.8

Limiting Reagents 3.9 2NO + 2O 2 2NO 2 NO is the ___________ reagent O 2 is the ___________ reagent

Do You Understand Limiting Reagents? In one process, 124 g of Al are reacted with 601 g of Fe 2 O 3 2Al + Fe 2 O 3 Al 2 O 3 + 2Fe Calculate the mass of Al 2 O 3 formed. g Almol Almol Fe 2 O 3 neededg Fe 2 O 3 needed OR g Fe 2 O 3 mol Fe 2 O 3 mol Al neededg Al needed 124 g Al 1 mol Al 27.0 g Al x 1 mol Fe 2 O 3 2 mol Al x 160. g Fe 2 O 3 1 mol Fe 2 O 3 x = 367 g Fe 2 O 3 Start with 124 g Alneed 367 g Fe 2 O 3 Have more Fe 2 O 3 (601 g) so Al is limiting reagent 3.9

Use limiting reagent (Al) to calculate amount of product that can be formed. g Almol Almol Al 2 O 3 g Al 2 O g Al 1 mol Al 27.0 g Al x 1 mol Al 2 O 3 2 mol Al x 102. g Al 2 O 3 1 mol Al 2 O 3 x = 234 g Al 2 O 3 2Al + Fe 2 O 3 Al 2 O 3 + 2Fe 3.9

___________ Yield is the amount of product that would result if all the limiting reagent reacted. ___________ Yield is the amount of product actually obtained from a reaction. % Yield = Actual Yield Theoretical Yield x Reaction Yield

Some Polyatomic Ions 2.7

Chemistry In Action: Chemical Fertilizers Plants need: N, P, K, Ca, S, & Mg 3H 2 (g) + N 2 (g) 2NH 3 (g) NH 3 (aq) + HNO 3 (aq) NH 4 NO 3 (aq) 2Ca 5 (PO 4 ) 3 F (s) + 7H 2 SO 4 (aq) 3Ca(H 2 PO 4 ) 2 (aq) + 7CaSO 4 (aq) + 2HF (g) fluorapatite