The reactant used up first in a reaction is called the limiting reactant. Excess reactants are those present in quantities greater than necessary to react with the quantity of the limiting reactant. CO(g) + 2H 2 (g) → CH 3 OH(l) Limiting Reactants 8.4

Limiting Reactants Consider the reaction between 5 moles of CO and 8 moles of H 2 to produce methanol. How many moles of H 2 are necessary in order for all the CO to react? How many moles of CO are necessary in order for all of the H 2 to react? 10 moles of H 2 required; 8 moles of H 2 available; limiting reactant. 4 moles of CO required; 5 moles of CO available; excess reactant. CO(g) + 2H 2 (g) → CH 3 OH(l)

Limiting Reactants oncord.org/public/student/chemicalreaction/particle_collisions.htmlhttp://mw.concord.org/modeler/showcase/simulation.html?s= oncord.org/public/student/chemicalreaction/particle_collisions.html oncord.org/public/student/chemicalreaction/explosion.htmlhttp://mw.concord.org/modeler/showcase/simulation.html?s= oncord.org/public/student/chemicalreaction/explosion.html hill.com/sites/ /student_view0/chapter8/animations.html# hill.com/sites/ /student_view0/chapter8/animations.html#

Worked Example 8.7 Alka-Seltzer tablets contain aspirin, sodium bicarbonate, and citric acid. When they come into contact with water, the sodium bicarbonate (NaHCO 3 ) and citric acid (H 3 C 6 H 5 O 7 ) react to form carbon dioxide gas, among other products. 3NaHCO 3 (aq) + H 3 C 6 H 5 O 7 (aq) → 3CO 2 (g) + 3H 2 O(l) + Na 3 C 6 H 5 O 7 (aq) The formation of CO 2 causes the trademark fizzing when the tablets are dropped into a glass of water. An Alka-Seltzer tablet contains g of sodium bicarbonate and g citric acid. Determine, for a single tablet dissolved in water, (a) which ingredient is the limiting reactant, (b) what mass of the excess reactant is left over when the reaction is complete, and (c) what mass of CO 2 forms.

Limiting Reactants The theoretical yield is the amount of product that forms when all the limiting reactant reacts to form the desired product. The actual yield is the amount of product actually obtained from a reaction. The percent yield tells what percentage the actual yield is of the theoretical yield. Activity: Why is % yield so important to a synthetic chemist working for a pharmaceutical company?

Worked Example 8.8 Aspirin, acetylsalicylic acid (C 9 H 8 O 4 ), is the most commonly used pain reliever in the world. It is produced by the reaction of salicylic acid (C 7 H 6 O 3 ) and acetic anhydride (C 4 H 6 O 3 ) according to the following equation: In a certain aspirin synthesis, g of salicylic acid and g of acetic anhydride are combined. Calculate the percent yield if g of aspirin are produced. C 7 H 6 O 3 salicylic acid C 4 H 6 O 3 acetic anhydride C 9 H 8 O 4 acetylsalicylic acid HC 2 H 3 O 2 acetic acid ++→

A list of the percent by mass of each element in a compound is known as the compound’s percent composition by mass. where n is the number of atoms of the element in a molecule or formula unit of the compound Percent Composition of Compounds 5.9

For a molecule of H 2 O 2 : Percent Composition of Compounds

Worked Example 5.13 Strategy Use Equation 5.1 to determine the percent by mass contributed by each element in the compound. Text Practice: Lithium carbonate, Li 2 CO 3, was the first “mood-stabilizing” drug approved by the FDA for the treatment of mania and manic-depressive illness, also known as bipolar disorder. Calculate the percent composition by mass of lithium carbonate.

General Trends in Reactivity Hydrogen (1s 1 )  Grouped by itself  Forms a cation with a +1 charge (H + )  Forms an anion with a -1 charge (H - )  Hydrides react with water to produce hydrogen gas and a base. CaH 2 (s) + H 2 O(l) → Ca(OH) 2 (aq) + H 2 (g) 8.5

Reactions of the Active Metals Group 1A Elements (ns 1, n ≥ 2)  Low IE  Never found in nature in pure elemental state  React with oxygen to form metal oxides  React with water to form metal hydroxides and H 2 gas. Alkali metals reacting with water sodiumpotassiumcesium

Reactions of the Active Metals Group 2A Elements (ns 2, n ≥ 2)  Less reactive than 1A  Some react with H 2 O to produce H 2  Some react with acid to produce H 2 Barium reacting with water

Reactions of Other Main Group Elements Group 3A elements (ns 2 np 1, n ≥ 2)  Metalloid (B) and metals (all others)  Al forms Al 2 O 3 with oxygen  Al forms +3 ions in acid  Others form +1 and +3 Finely-divided aluminum sprinkled into a flame to form Al 2 O 3

Reactions of Other Main Group Elements Group 4A elements (ns 2 np 2, n ≥ 2)  Nonmetal (C); metalloids (Si, Ge) and others metals  Generally avoid forming formal charges by sharing valence electrons  Elements near the bottom of the periodic table (Sn, Pb) react with acid to give charges of 2+ or 4+ because outer electrons are loosly held.

Reactions of Other Main Group Elements Group 5A elements (ns 2 np 3, n ≥ 2)  Nonmetal (N 2, P), metalloid (As, Sb), and metal (Bi)  Nitrogen, N 2, forms variety of oxides  Phosphorus, P 4  As, Sb, Bi (crystalline)  HNO 3 and H 3 PO 4 important industrially

Reactions of Other Main Group Elements Group 6A elements (ns 2 np 4, n ≥ 2)  Nonmetals (O, S, Se)  Oxygen, O 2  Sulfur, S 8  Selenium, Se 8  Metalloids (Te, Po)  Te, Po (crystalline)  SO 2, SO 3, H 2 S, H 2 SO 4

Reactions of Other Main Group Elements Group 7A elements (ns 2 np 5, n ≥ 2)  All diatomic  Do not exist in elemental form in nature  Form ionic “salts”  Form molecular compounds with each other  React with hydrogen to form hydrogen halides

Reactions of Other Main Group Elements Group 8A elements (ns 2 np 6, n ≥ 2)  All monatomic  Filled valence shells  Considered “inert” until 1963 when Xe and Kr were used to form compounds

Comparison of Group 1A and 2A and Group B Elements  Have loose valence electron(s)  Properties differ  Group 1B much less reactive than 1A  High IE of 1B - incomplete shielding of nucleus by inner “d” - outer “s” electron of 1B strongly attracted to nucleus  1B metals often found elemental in nature (coinage metals)

Study Guide for Sections 8.4, 5.9, 8.5 DAY 22, Terms to know: Sections 8.4, 5.9, 8.5 limiting reagent, excess reagent, theoretical yield, actual yield, percent yield, percent composition by mass DAY 22, Specific outcomes and skills that may be tested on exam 4: Sections 8.4, 5.9, 8.5 Given starting quantities of reactants, be able to determine which is the limiting reagent and which is in excess and quantify the amount in excess Given quantities of reactants, be able to determine the theoretical yield for any of the products Given any two of the three following quantities, be able to calculate the third: theoretical yield, actual yield, and percent yield Given a chemical formula, be able to calculate the mass percent composition for any element in the compound Be able to use pressure changes during a chemical reaction to determine how many moles of reaction have occurred and relate that to the percent yield

Extra Practice Problems for Sections 8.4, 5.9, 8.5 Complete these problems outside of class until you are confident you have learned the SKILLS in this section outlined on the study guide and we will review some of them next class period. VC8.1 VC8.2 VC8.3 VC

Prep for Day 23 Must Watch videos: (acid/base, crash course chemistry) (acid/base, Bozeman) 0cpNw&list=PLXxSuXRSRzwDPAH0H54IQaA1bD3i48zr7&index=1 (acid/base, Tyler DeWitt) 0cpNw&list=PLXxSuXRSRzwDPAH0H54IQaA1bD3i48zr7&index=1 Other helpful videos: (UC-Irvine, lectures 18) Read Sections 9.3, 9.5 (pages ), 9.6