Reactions in Aqueous Solutions Unit 4: Reactions in Aqueous Solutions Day 3: Metathesis Reactions and Intro to Gravimetric Analysis

Warm Up ANSWER: The following questions: Write out the reaction between ammonium sulfide and barium chloride Balance equation and identify the precipitate If you are given 2 grams of ammonium sulfide, how much precipitate would you have with 0% error? TIME: 12 MINUTES WHEN DONE: Show me for a stamp

Agenda Double Displacement/Metathesis Reactions Ways to Represent Metathesis Rxn Guided Inquiry: Net Ionic Equations Intro to Gravimetric Analysis Work Time

Lecture Notes Topics: What’s Important? Definitions: Electrolyte (strong vs. weak) Non-electrolyte Dissociate Precipitate Solubility (and guideline table) Metathesis Reactions Types of Equations: Molecular Complete ionic Net ionic Neutralization Strong Acids vs. Strong Bases

Lecture Notes Topics: What’s Important? Processes How to identify strong vs. weak electrolytes How to predict precipitates How to predict metathesis reactions How to write a molecular equation How to write a net ionic equation How to write a neutralization reaction

What do I need to memorize and what do I need to just practice with? Memorize Practice Definitions Table 4.1, p. 129 Solubility Guidelines Table 4.2, p. 134 Activity Series, p. 144 Table 4.3, p. 135 Steps for Molecular Eq Molarity equation Steps for Net Ionic Eq Dilution equation Steps for Neutralization

Review Definitions Solutions are defined as homogeneous mixtures of two or more pure substances. Solutions are made of solvents and solutes. Let’s say you make a chocolate milk “SOLUTION” by mixing Nestle Quik powder with Milk. WHICH IS THE SOLUTE? NESTLE QUIK OR MILK? Solute = nestle quik

Aqueous Solutions Ionic Compounds: Dissociate completely (separate into ions) Molecular Compounds: Sometimes dissolve, but DO NOT dissociate (because molecular compounds do not “transfer” electrons, they “share” electrons)

Electrolytes and Nonelectrolytes An electrolyte is a substance that dissociates into ions when dissolved in water. A nonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so. Classify the following compounds: NaCl, CH3OH, HCl, C3H8O3, NH3PO4, LiOH, HNO3, NH3, C12O22H11 STRONG WEAK NON- ELECTROLYTE NaCl NH3PO4 CH3OH HCl NH3 C3H8O3 LiOH C12O22H11 HNO3

METATHESIS REACTIONS Molecular Equations Complete Ionic Equations Net Ionic Equations Neutralization Reactions Gas Forming Reactions

Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means “to transpose.” It appears as though the ions in the reactant compounds exchange, or transpose, ions, as seen in the equation below. AgNO3(aq) + KCl(aq)  AgCl(s) + KNO3(aq)

Completing and Balancing Metathesis Equations Steps to follow Use the chemical formulas of the reactants to determine which ions are present. Write formulas for the products: cation from one reactant, anion from the other. Use charges to write proper subscripts. Check your solubility rules. If either product is insoluble, a precipitate forms. Balance the equation.

Which of these are soluble? (NH4)2S, CaCO3, NaOH, Ag2SO4, Pb(CH3COOH)2

Predict the identity of the precipitate… When MgCl2 and CaS are mixed. Write the balanced equation. MgCl2 + CaS = MgS + CaCl2

Predict the identity of the precipitate… When solutions of Fe2(SO4)3 and LiOH are mixed. Write the balanced equation. Fe2(SO4)3 + LiOH = Fe(OH)3 + Li2SO4

Yes or No? Will a precipitate form when Ba(NO3)2 and KOH are mixed? Ba(NO3)2 + KOH = Ba(OH)2 + KNO3 (No, both products are soluble)

Ways to Write Metathesis Reactions Molecular Net Ionic Complete Ionic

AgNO3(aq) + KCl(aq)  AgCl(s) + KNO3(aq) Molecular Equation The molecular equation lists the reactants and products without indicating the ionic nature of the compounds. AgNO3(aq) + KCl(aq)  AgCl(s) + KNO3(aq)

Complete Ionic Equation In the complete ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions. This more accurately reflects the species that are found in the reaction mixture. Ag+(aq) + NO3−(aq) + K+(aq) + Cl−(aq)  AgCl(s) + K+(aq) + NO3−(aq)

Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. The ions crossed out are called spectator ions, K+ and NO3−, in this example. The remaining ions are the reactants that form the product—an insoluble salt in a precipitation reaction, as in this example. Ag+(aq) + NO3−(aq) + K+(aq) + Cl−(aq)  AgCl(s) + K+(aq) + NO3−(aq)

Writing Net Ionic Equations Write a balanced molecular equation. Dissociate all strong electrolytes. Cross out anything that remains unchanged from the left side to the right side of the equation. Write the net ionic equation with the species that remain.

Writing Net Ionic Equations Write the net ionic equation for the reaction that occurs when aqueous solutions of silver nitrate and potassium phosphate are mixed.

Guided Inquiry: Net Ionic Equations WORK ON: Guided Inquiry Questions REVIEW PAGE 1 & 2: In 11 minutes REVIEW REST: Next class TIME: 22 MINUTES WHEN DONE: Check answers with ANSWER KEY

Intro to Gravimetric Analysis WATCH VIDEO: On Gravimetric Analysis TAKE NOTES: On example problem TIME: 14 MINUTES WHEN DONE: Write Questions in the Margins https://www.youtube.com/watch?v=WBg-yh8qk94