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

2. 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

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

4. 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

5. 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

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

7. 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

8. 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)

9. 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 NH C3H8O3
LiOH C12O22H11
HNO3

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

11. 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)

12. 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.

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

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

15. 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

16. 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)

17. Ways to Write Metathesis Reactions
Molecular
Net Ionic
Complete Ionic

18. 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)

19. 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)

20. 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)

21. 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.

22. 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.

23. 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

24. Intro to Gravimetric Analysis
WATCH VIDEO: On Gravimetric Analysis TAKE NOTES: On example problem TIME: 14 MINUTES WHEN DONE: Write Questions in the Margins