Reactions in Aqueous Solutions Unit 4: Reactions in Aqueous Solutions Day 5: Metathesis Reactions and Gravimetric Analysis

Warm Up WHICH CHEMICAL EQUATION IS CORRECT? HINT: Look at solubility rules Fe2(SO4)3 (aq) + 3 Li2S (aq) Fe2S3 (aq) + 3 Li2SO4 (aq) CaCl2 (aq) + 2 NH4OH (aq) Ca(OH)2 (s) + 2 NH4Cl (aq) Nal2 (aq) + AgNO3 (aq) NaNO3 (aq) + AgI2 (s) TIME: 8 MINUTES WHEN DONE: Show me for a stamp

Warm Up 11/30 Which set includes only substances that produce electrolytes in water? NaBr, KCl, MgSO4 C6H12O6, CH3OH, C6H6 HCl, NH3, Cl2, N2 SiO2, CaCO3, H2SO4 Answer: a

Which set includes only substances that produce electrolytes in water? NaBr, KCl, MgSO4 C6H12O6, CH3OH, C6H6 HCl, NH3, Cl2, N2 SiO2, CaCO3, H2SO4 Answer: a

Pb(NO3)2 + 2 KI  PbI2 + 2 KNO3 The physical evidence that the above reaction occurs is an explosion. the formation of a gas. that the solution boils. the formation of a precipitate. Answer: d

Pb(NO3)2 + 2 KI  PbI2 + 2 KNO3 The physical evidence that the above reaction occurs is an explosion. the formation of a gas. that the solution boils. the formation of a precipitate. Answer: d

H2SO4 and NaOH HNO3 and CaCl2 Ba(NO3)2 and Na3PO4 LiCl and SrI2 Which pair of compounds will produce a precipitate if solutions of appropriate concentrations are mixed together? H2SO4 and NaOH HNO3 and CaCl2 Ba(NO3)2 and Na3PO4 LiCl and SrI2 Answer: c

H2SO4 and NaOH HNO3 and CaCl2 Ba(NO3)2 and Na3PO4 LiCl and SrI2 Which pair of compounds will produce a precipitate if solutions of appropriate concentrations are mixed together? H2SO4 and NaOH HNO3 and CaCl2 Ba(NO3)2 and Na3PO4 LiCl and SrI2 Answer: c

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

Acids The Swedish physicist and chemist S. A. Arrhenius defined acids as substances that increase the concentration of H+ when dissolved in water. Both the Danish chemist J. N. Brønsted and the British chemist T. M. Lowry defined them as proton donors.

Bases Arrhenius defined bases as substances that increase the concentration of OH− when dissolved in water. Brønsted and Lowry defined them as proton acceptors (react with H+)

Strong or Weak? Strong acids completely dissociate in water; weak acids only partially dissociate. Strong bases dissociate to metal cations and hydroxide anions in water; weak bases only partially react to produce hydroxide anions.

Learning Check

Strong vs. Weak Electrolytes If we remember the common strong acids and bases (table 4.2) and that NH3 is a weak base, we can make reasonable predictions about the electrolytic strength of a lot of compounds!

Acid-Base Reactions In an acid–base reaction, the acid (H2O above) donates a proton (H+) to the base (NH3 above). Reactions between an acid and a base are called neutralization reactions. When the base is a metal hydroxide, water and a salt (an ionic compound) are produced.

Ways to Write Metathesis Reactions Molecular Neutralization Reactions (Not all form precipitate!) Net Ionic Complete Ionic

Neutralization Reactions When a strong acid (like HCl) reacts with a strong base (like NaOH), the net ionic equation is circled below: HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) H+(aq) + Cl−(aq) + Na+(aq) + OH−(aq)  Na+(aq) + Cl−(aq) + H2O(l) H+(aq) + OH−(aq)  H2O(l)

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 + 6 LiOH = 2 Fe(OH)3 + 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.

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 DUE: 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