Predicting products
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This document provides an overview of predicting products for the AP Chemistry exam question #4. It begins by explaining that question #4 asks students to write balanced net ionic equations for 3 given chemical reactions. It then reviews how to write net ionic equations, including dissociating ionic compounds and identifying spectator ions. The document outlines the steps to predict products for double displacement reactions, including precipitation reactions where an insoluble compound forms, and acid-base reactions where a salt and water form. It provides examples of writing net ionic equations for different reaction types that could appear in the AP question. The goal is to teach students the process for systematically predicting products to answer question #4.
Predicting products
- 1. AP Chemistry Rapid Learning Series - 09 Rapid Learning Center Chemistry :: Biology :: Physics :: Math Rapid Learning Center Presents … p g Teach Yourself AP Chemistry Visually in 24 Hours 1/67 http://www.RapidLearningCenter.com Predicting Products AP Ch i t R id Learning Series Chemistry Rapid L i S i Wayne Huang, PhD Kelly Deters, PhD Russell Dahl, PhD Elizabeth James, PhD Debbie Bilyen, M.A. © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com Rapid Learning Center www.RapidLearningCenter.com/ © Rapid Learning Inc. All rights reserved. 1
- 2. AP Chemistry Rapid Learning Series - 09 Learning Objectives By viewing this tutorial you will learn… How to answer the AP Exam question #4 by: Predicting Products Writing Net Ionic Reactions 3/67 Concept Map Previous content Chemistry New content Studies Matter Undergoes Chemical Equations Shown in Chemical Changes Different categories of Written in Chemical Reactions Different categories can be used to Predict Products of a Reaction 4/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 2
- 3. AP Chemistry Rapid Learning Series - 09 What is the AP Free Response Question #4? 5/67 AP Predicting Products The AP exam has a question that is unique to the exam. It’s always q y question #4 of the Free Response section. p The question has 3 required reactions—there is no choice Part I gives reactants in word form It asks for the balanced net ionic reaction given those reactants 1 point is earned for the correct reactant formulas. Up to 2 points are earned for the correct product formulas. 1 point for correct balancing balancing. Part II asks a question about the reaction Questions may ask about the type of reaction, stoichiometry, physical observations during the reaction, etc. Earn 1 point for correct answer to this question. 6/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 3
- 4. AP Chemistry Rapid Learning Series - 09 Predicting Products is Difficult! A difficult task – This is a very difficult question for most AP students, but you can be successful. This tutorial will systematically introduce you to each type of reaction included in the question and give tips! However, much of a students’ ability to answer these questions relates to experience—the more reactions you see and work with throughout your course, the better you’ll be able to predict products! 7/67 Net Ionic Equations 8/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 4
- 5. AP Chemistry Rapid Learning Series - 09 Definition: Net Ionic Equation When an ionic compound dissolves in water, the ions dissociate (separate) and move freely throughout the solution. Ionic Equation – Any soluble ionic compound is dissociated into ions. Net Ionic Equation – Only ions necessary for the chemical reaction y are shown. 9/67 When to Dissociate a Compound How do you know what to dissociate and what not to dissociate? DO dissociate DO NOT EVER dissociate Soluble IONIC compounds when aqueous COVALENT compounds (soluble or not) Strong acids and bases in water Weak acids and bases The AP instructions say to assume reactants are aqueous solutions unless otherwise stated! Solids, liquids or gases (even ionic and strong acids/bases!) 10/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 5
- 6. AP Chemistry Rapid Learning Series - 09 Ionic Solubility Rules Look up the anion in the left column to see which cations it forms insoluble compounds with. Forms insoluble compounds with NO3CH3COO- Ag+ Cl-, Br-, I- Ag+, Pb2+, Hg22+, Ti+ SO42- Ag+, Pb2+, Ba2+, Sr2+, Ca2+ CrO42- Ag+, Pb2+, Ba2+, Sr2+ S2- All cations except NH4+, column 1 & 2 OH- All cations except NH4+, Column 1, Ba2+ and Sr2+ CO32-, PO43- 11/67 No common cations All cations except NH4+, Column 1 (except Li+) NH4+, Na+ and K+ are soluble with all common anions. Using Ionic Solubility Rules Will each of the following compounds be soluble? NaNO3 NO3- is insoluble with no common cations Soluble AgCl Cl- is insoluble with Ag+, Pb2+, Hg22+, Ti+ Insoluble Mg(OH)2 OH- is insoluble except with NH4+, cations of column 1, Ba2+, Sr2+ Insoluble Na2Cr2O7 There is no rule for Cr2O72-, but Na+ is soluble with all anions Soluble 12/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 6
- 7. AP Chemistry Rapid Learning Series - 09 Common Strong Acids and Bases There are only a few common strong acids and bases to remember—the rest will most likely be weak! Strong Acids HCl, HBr, HI, HNO3, HClO3, HClO4 Strong Bases NaOH, KOH, Ca(OH)2, Ba(OH)2, Sr(OH)2 13/67 Writing Net Ionic Equations - 1 1 Dissociate all soluble ionic compounds Only dissociate soluble, ionic compounds in water (“aq”) Only subscripts within a polyatomic ion remain as subscripts All other subscripts are moved to coefficients. Cross out any ion that is dissociated on both sides 2 These are called spectator ions 3 Re-write the final net ionic equation Examples: Write the net ionic equation for: 2 NaOH (aq) + Mg(NO3)2 (aq) Mg(OH)2 (s) + 2 NaNO3 (aq) 2 1 2 Na+ + 2 OH- + Mg+2 + 2 NO3Mg+2 + 2 OH- Mg(OH)2 (s) + 2 Na+ + 2 NO3Mg(OH)2 (s) 3 14/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 7
- 8. AP Chemistry Rapid Learning Series - 09 Writing Net Ionic Equations - 2 1 Dissociate all soluble ionic compounds Only dissociate soluble, ionic compounds in water (“aq”) Only subscripts within a polyatomic ion remain as subscripts All other subscripts are moved to coefficients. 2 Cross out any ion that is dissociated on both sides 3 Re-write the final net ionic equation These are called spectator ions. Examples: Write the net ionic equation for: AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq) 2 1 Ag+ + NO3- + Na+ + ClAg+ + Cl- AgCl (s) + Na+ + NO3AgCl (s) 3 15/67 Double Displacement - Precipitation 16/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 8
- 9. AP Chemistry Rapid Learning Series - 09 Definition - Precipitation Reaction Precipitation Reaction – One type of Double Displacement reaction: Two soluble compounds react to form an insoluble compound (the precipitate). Recognizing this type – 2 ionic compounds in solution. 17/67 Designating a Precipitate If an insoluble compound is formed from aqueous solutions of two soluble compounds, it is a l ti ft l bl d i precipitate and should be designated with a “(s)”. Example: p AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq) Precipitate 18/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 9
- 10. AP Chemistry Rapid Learning Series - 09 Double Displacement – Precipitation 1 1 Determine it’s Double Displacement (two compounds, each with a cation and anion). CaCl2 (aq) + AgNO3 (aq) 19/67 Double Displacement – Precipitation 2 2 Combine the cation of the first reactant with the anion of the second reactant. CaCl2 (aq) + AgNO3 (aq) CaCl2 (aq) + AgNO3 (aq) CaNO3 20/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 10
- 11. AP Chemistry Rapid Learning Series - 09 Double Displacement – Precipitation 3 3 Combine the cation of the second reactant with the anion of the first reactant. CaCl2 (aq) + AgNO3 (aq) CaCl2 (aq) + AgNO3 (aq) CaNO3 + AgCl 21/67 Double Displacement – Precipitation 4 4 Remember to write cations first … & balance charges with subscripts when writing formulas CaCl2 (aq) + AgNO3 (aq) CaCl2 (aq) + AgNO3 (aq) Ca(NO3)2 + AgCl 22/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 11
- 12. AP Chemistry Rapid Learning Series - 09 Double Displacement – Precipitation 5 5 Determine the precipitate using solubility rules. CaCl2 (aq) + AgNO3 (aq) CaCl2 (aq) + AgNO3 (aq) Ca(NO3)2 (aq) + AgCl (s) 23/67 Double Displacement – Precipitation 6 6 Write the net ionic equation & check to be sure it’s balanced. Don’t balance until the end as it’s often easier to balance the net ionic than the original equation! CaCl2 (aq) + AgNO3 (aq) CaCl2 (aq) + AgNO3 (aq) Ca+2 + Cl-1 + Ag+1 + NO3-1 Cl-1 + Ag+1 Ca(NO3)2 (aq) + AgCl (s) Ca+2 + 2 NO3-1 + AgCl AgCl It’s balanced. 24/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 12
- 13. AP Chemistry Rapid Learning Series - 09 Double Displacement - Acid Base 25/67 Definition - Acid/Base Reaction Acid-Base reaction – One type of Double Displacement reaction: An acid and a base react to form salt and water. Recognizing this type – Acid (begins with “H”) and a base (ends with “OH” or is NH3). 26/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 13
- 14. AP Chemistry Rapid Learning Series - 09 Double Displacement - Acid/Base 1 1 Determine it’s Double Displacement: acid-base (contains an acid and base for reactants) HNO3 (aq) + Na OH (aq) 27/67 Double Displacement - Acid/Base 2 2 Combine the cation of the first reactant with the anion of the second reactant. HNO3 (aq) + Na OH (aq) H NO3 (aq) + Na OH (aq) H2O 28/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 14
- 15. AP Chemistry Rapid Learning Series - 09 Double Displacement - Acid/Base 3 3 Combine the cation of the second reactant with the anion of the first reactant. HNO3 (aq) + Na OH (aq) H NO3 (aq) + Na OH (aq) HOH + NaNO3 29/67 Double Displacement - Acid/Base 4 4 Remember to write cations first … & balance charges with subscripts when writing formulas f l HNO3 (aq) + Na OH (aq) H NO3 (aq) + Na OH (aq) H2O + NaNO3 30/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 15
- 16. AP Chemistry Rapid Learning Series - 09 Double Displacement - Acid/Base 5 5 Write the net ionic equation & be sure it’s balanced. DO NOT dissociate weak acids and bases - only strong ones that are dissolved in water (Aqueous)! DO NOT dissociate water! HNO3 (aq) + Na OH (aq) H NO3 (aq) + Na OH (aq) H+ + NO3-1 + Na+1 + OH-1 H+ + OH- H2O + NaNO3 H2O + Na+ + NO3-1 H2O It’s balanced. 31/67 An Example With a Weak Acid - 1 1 Determine it’s Double Displacement: acid-base (contains an acid and base for reactants). H2CO3 (aq) + Na OH (aq) 32/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 16
- 17. AP Chemistry Rapid Learning Series - 09 An Example With a Weak Acid - 2 2 Combine the cation of the first reactant with the anion of the second reactant. H2CO3 (aq) + Na OH (aq) H2CO3 (aq) + Na OH (aq) HOH 33/67 An Example With a Weak Acid - 3 3 Combine the cation of the second reactant with the anion of the first reactant H2CO3 (aq) + Na OH (aq) H2CO3 (aq) + Na OH (aq) H2O + NaCO3 34/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 17
- 18. AP Chemistry Rapid Learning Series - 09 An Example With a Weak Acid - 4 4 Remember to write cations first … & balance charges with subscripts when writing formulas. H2CO3 (aq) + Na OH (aq) H2CO3 (aq) + Na OH (aq) H2O + Na2CO3 35/67 An Example With a Weak Acid - 5 5 Write the net ionic equation & be sure it’s balanced. DO NOT dissociate weak acids and bases - only strong ones that are dissolved in water (Aqueous)! DO NOT dissociate water! H2CO3 (aq) + Na OH (aq) H2CO3 (aq) + Na OH (aq) H2CO3 + Na+1 + OH-1 H2CO3 + 2 OH- H2O + Na2CO3 H2O + 2 Na+ + CO3-2 It’s -2 balanced. 2 H2O + CO3 36/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 18
- 19. AP Chemistry Rapid Learning Series - 09 Decomposition 37/67 Definition - Decomposition Decomposition – One molecule decomposes into more than one thing. Recognizing this type – Only one reactant. Often uses “heated” in description. 38/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 19
- 20. AP Chemistry Rapid Learning Series - 09 Common Decompositions Metal carbonates – Decompose to form metal oxide and carbon dioxide. Ammonium salts – Decompose to form ammonia gas. 39/67 Decomposition - Examples (NH4)2CO3 (s) 2 NH3 + CO2 + H2O Hint: Carbonates d Hi t C b t decompose t f to form CO2 as one of the products! f th d t ! MgCO3 (s) 6 NH4NO3 (s) MgO + CO2 8 NH3 + 2 N2 + 9 O2 Hint: All of these are solids or gases - none dissociate! 40/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 20
- 21. AP Chemistry Rapid Learning Series - 09 Combination 41/67 Definition - Combination Combination – More than one molecule combine to form one molecule. Recognizing this type – Something being added to water OR two compounds or elements being “heated” together. 42/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 21
- 22. AP Chemistry Rapid Learning Series - 09 Common Combination Reactions Metal or metal oxide added to water – Produce a base. Non-metal or non-metal oxide added to water – Produce an acid. Strong acids and bases produced MUST be dissociated. Weak ones MUST be left together. 43/67 Combination Examples BaO + H2O BaO + H2O Ba(OH)2 Ba+2 + 2 OH-1 Hint: Remember to dissociate soluble ionic compounds, strong acids and strong bases when something is in water! SO2 + H2O 3 Mg + N2 H2SO3 Mg3N2 44/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 22
- 23. AP Chemistry Rapid Learning Series - 09 Complex Ion Formation 45/67 Definition - Complex Ion Formation Complex Ion – A species with several electron donating polyatomic ions bonded to a single metal atom or ion. Recognizing this type – Something reacted with “excess” hydroxide, cyanide or ammonia. ammonia 46/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 23
- 24. AP Chemistry Rapid Learning Series - 09 Common Complex Ions Cyanide complex ions – Ag(CN)2-1, Fe(SCN)+2 Ammonia complex ions – Cu(NH3)4+2, Zn(NH3)4+2, Ag(NH3)2+1, Ni(NH3)6+2 Hydroxide complex ions – Al(OH)4-1, Zn(OH)4-2 47/67 Complex Ion Examples NaCN (aq) + AgNO3 (aq) 2 CN-1 + Ag+1 g Ag(CN)2-1 + NaNO3 Ag(CN)2-1 g( ) Hint: Remember to cancel out ions that dissociate on both sides of the reaction when writing the net ionic reaction. 2 NH3 (aq) + AgCl (s) NH3 (aq) + NiSO4 (aq) 6 NH3 + Ni+2 Ag(NH3)2+1 + Cl-1 Ni(NH3)6+2 + SO4-2 NI(NH3)6+2 48/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 24
- 25. AP Chemistry Rapid Learning Series - 09 Combustion 49/67 Definition - Combustion Combustion – Combination with O2. Recognizing this type – Something reacted with O2 . 50/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 25
- 26. AP Chemistry Rapid Learning Series - 09 Combustion Examples 2 CH3CH2OH (g) + 7 O2 (g) 4 CO2 + 6 H2O Hint: You’ll learn how to write the simple organic molecules You ll from words in a future tutorial (Descriptive and Organic Chemistry). C2H4 (g) + 3 O2 (g) 2 CO2 + 2 H2O Hint: If hydrocarbons (hydrogen, carbon and oxygen containing) are added to O2, the products are ALWAYS CO2 & H2O. p CS2 + 4 O2 CO2 + 2 SO2 51/67 Redox 52/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 26
- 27. AP Chemistry Rapid Learning Series - 09 Definition - Redox Redox – Reduction/Oxidation. Charges are changed - one increases and one decreases. Recognizing this type – Single replacement reaction or one with a common oxidizer (NO3-1, MnO4-1, Cr2O7-2, H2O2). 53/67 Redox Examples Zn (s) + CuSO4 (aq) ZnSO4 + Cu Zn+2 + Cu Zn + Cu+2 Pb (s) + AgNO3 (aq) Pb + 2 Ag+ Ag + Pb(NO3)2 2 Ag + Pb+2 Don’t forget you must balance charge as well as number of atoms! This one isn’t balanced as it first appears! 54/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 27
- 28. AP Chemistry Rapid Learning Series - 09 Going from “Word” Word Reactants to “Formula” Reactants 55/67 Writing the Reactants The question will give you – The reactants in word form with word clues about state of matter. Writing the reactants – 1 point is awarded for each of the 3 required sets of reactants that you write correctly in formula form. (they must be dissociated correctly to get the 1 point). point) 56/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 28
- 29. AP Chemistry Rapid Learning Series - 09 Know What Terms Mean They use several terms that mean the similar things. Solid, powdered, metal, filings, strip = solid (don’t dissociate) Solution = dissociate any soluble ionic compounds or strong acid/base, including in saturated solutions. Suspension = a solid precipitate spread throughout water; doesn’t dissociate. If there is a solution or water in the reactants reactants— assume that the water (solution) is still there in the products and break up any soluble ionic compounds or strong acids or bases in the products. Acidified solution = make H+ one of the reactants 57/67 Part II Questions 58/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 29
- 30. AP Chemistry Rapid Learning Series - 09 What are the Part II Questions? There is a question after each of the 3 reactions that focuses on the meaning of the reaction. It might ask: Type of reaction To identify a participant in the reaction (species being oxidized, etc.) About the stoichiometric ratio of the equation About physical observations during the reaction 59/67 Using Part II Questions as Hints You might be able to gain hints about the reaction in Part I from the Part II question. A strip of magnesium is added to a solution of silver nitrate. What is the change in oxidation number of the magnesium? The P t Th Part II question tells you that ti t ll th t the reaction in Part I is a Redox reaction! 60/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 30
- 31. AP Chemistry Rapid Learning Series - 09 Example 1 A strip of magnesium is added to a solution of silver nitrate. Mg (s) + AgNO3 (aq) Mg + 2 Ag+1 Mg(NO3)2 (aq) + Ag (s) Mg+2 + 2 Ag What is the change in oxidation number of the magnesium? Mg is going from 0 to +2 61/67 Example 2 Zinc metal is placed in a solution of copper (II) nitrate. Zn (s) + Cu(NO3)2 (aq) Zn + Cu+2 Zn(NO3)2 (aq) + Cu (s) Zn+2 + Cu Describe the color change during the process. Cu+2 is blue. As it reacts to form Cu solid and Zn+2 the blue color will fade as Zn+2 is colorless. 62/67 © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 31
- 32. AP Chemistry Rapid Learning Series - 09 Tips for AP Free Response Question #4 63/67 Helpful Hints for Question #4 1 2 Pay attention to the states of matter of the reactants—don’t dissociate solids, liquids or gases…only aqueous solutions! 3 Be sure to cross out spectator ions! 4 There is always a reaction…if you think everything will cancel out in the ionic equation, go back and find your mistake! o r 5 Be sure to balance the final net ionic equation (don’t do the initial equation…the final one is easier) 6 64/67 Know the solubility rules & list of strong acids/bases so you’ll know what to dissociate! Use the Part II questions as hints for what the reaction might be in Part I © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 32
- 33. AP Chemistry Rapid Learning Series - 09 Learning Summary Be sure to balance the final net ionic reaction. Question 4 requires you to write balanced net ionic reactions after predicting products. Know the solubility rules and how to write net ionic reactions. Use the Part II question as a hint for the products on Part I. Know what common phrases are used to describe states of matter. 65/67 Congratulations You have successfully completed the core tutorial Predicting Products Rapid Learning Center © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 33
- 34. AP Chemistry Rapid Learning Series - 09 Rapid Learning Center Chemistry :: Biology :: Physics :: Math What’s N t Wh t’ Next … Step 1: Concepts – Core Tutorial (Just Completed) Step 2: Practice – Interactive Problem Drill Step 3: Recap – Super Review Cheat Sheet Go for it! 67/67 http://www.RapidLearningCenter.com © Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com 34