Reactions in Aqueous Solution - Wayzata Public Schools

Reactions in Aqueous Solution

AP Chemistry – Chapter 4

Jodi Grack; Wayzata High School; Images from Zumdahl Chemistry 6th edition

Reactions in Aqueous Solution • Fundamental factor that causes reaction involving ions to occur is the starting ions are removed from solution. Ways this is accomplished: 1) Formation of a precipitate 2) Formation of a gas 3) Formation of a primarily molecular species 4) Form original ions into different ions. (oxidation - reduction) Jodi Grack; Wayzata High School; Images from Zumdahl Chemistry 6th edition

1) Precipitation Reactions Use solubility Rules ---> (table 4.1 pg. 144) (desk tops or handout)

Most nitrates (NO3-) are soluble. Most salts containing the alkali metal ions (Li+, Na+, K+, Cs+, Rb+) and the ammonium ion (NH4+) are soluble. 3. Most chloride, bromide, and iodide salts are soluble. 1. 2.

Exceptions: Ag+, Pb2+, and Hg22+. 4.

Most sulfate salts are soluble. Exceptions: BaSO4, PbSO4, HgSO4, and CaSO4.

5.

Most hydroxide are only slightly soluble. Exceptions: Group I & Calcium down in Group II.

6.

Most sulfide (S2-), carbonate (CO32-), chromate (CrO42-), and phosphate (PO43-) salts are only slightly soluble. S2- exceptions: Group I, Group II, NH4+ 3- exceptions: + Grack; Wayzata High School; Images from CO32-, CrO42-,JodiPO Group I, NH 4 4 Zumdahl Chemistry 6th edition

Solubility Rules Put these in a special “spot.” I recommend

starting a small (1/2 inch) 3-ring binder for only predicting reactions papers. MEMORIZE! We’ll try to quiz on these rules daily this unit.


1) Precipitation Reactions 1st example - Mix solutions of Ba(NO3)2 and Na2CO3. What happens?


1) Precipitation Reactions 2nd example - Mix solutions of CuCl2 and NaOH. What happens?


1) Precipitation Reactions 3rd example - Mix solutions of MgCl2 and KNO3. What happens?


Precipitate Colors

PbI2

HgCl2

AgCl (white)


HgS

Precipitate Colors Cu2+(aq) + 2NH3(aq) + 3 H2O (l) Cu(OH)2(s) + 2NH4+ (aq)

Cu(OH)2 (s) + 4 NH3 (aq) [Cu(NH3)4]2+ (aq) + 2OH- (aq)

Cu2+ (aq) + 2OH- (aq) Cu(OH)2 (s)


2) Gas formation Reactions – (H2S, CO2, SO2, NH3) H2CO3

Æ H2O + CO2

_________ Æ H2O + SO2 _________ Æ H2O + NH3 _________ Æ H2S (g)


2) Gas formation Reactions – (H2S, CO2, SO2, NH3) 4th example - Mix solutions of Na2CO3 and HCl. What happens?


3) Acid-Base Reactions Acids form H+ ions in solution

Difference between strong and weak acids: * Must know 6 strong acids - any other acid is weak


3) Acid-Base Reactions Strong Acid Reaction:

Weak Acid Reaction: Ex. 1.00 M HF: [HF] = 0.97 M, [H+] = [F-] = 0.03 M 3% ionized Jodi Grack; Wayzata High School; Images from Zumdahl Chemistry 6th edition

3) Acid-Base Reactions EXAMPLES - (Species present at highest concentration is written as the reactant.) A) Strong Acid - Strong Base HCl + Ca(OH)2 Net ionic equation:


3) Acid-Base Reactions EXAMPLES - (Species present at highest concentration is written as the reactant.) B) Strong Acid - Weak Base HCl + NH3 Net ionic equation:


3) Acid-Base Reactions EXAMPLES - (Species present at highest concentration is written as the reactant.) C) Weak Acid - Strong Base HF + NaOH Net ionic equation


REVIEW OF ELECTROLYTES & NET IONIC REACTIONS Strong Electrolytes – exist 100% as ions in solution Weak Electrolytes – exists partially as ions in solution Non-electrolytes – do NOT exist as ions


REVIEW OF ELECTROLYTES


Problem Set 4.1 Summary Problem Set 4.1 is all about writing net ionic reactions. When writing an ionic equation write everything that exists

as ions as ions. Use Solubility Rules on Write as Ions pg. 141 (or rules below Aqueous (soluble) ionic compound the overhead) to determine solubility. Strong acids Write as molecules Insoluble ionic compounds (or any ionic cpd not in solution) Weak acids Molecular compounds Jodi Grack; Wayzata High School; Images from Zumdahl Chemistry 6th edition

Problem Set 4.1 Summary

See back page of your note packet!

NOTE: The strong bases are also the soluble hydroxides. Ex. A solution of sodium hydroxide is mixed with hydrochloric acid Total ionic: Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) Æ H2O (l) + Na+ (aq) + Cl-(aq) Net ionic: OH-(aq) + H+(aq) Æ H2O(l) Ex. Magnesium hydroxide is mixed with hydrochloric acid Total ionic: Mg(OH)2 (s) + 2 H+ (aq) + 2 Cl- (aq) Æ 2 H2O(l) + Mg2+(aq) + 2 Cl-(aq) Net ionic: Mg(OH)2 (s) + 2 H+ (aq) Æ 2 H2O (l) + Mg2+ (aq) Jodi Grack; Wayzata High School; Images from Zumdahl Chemistry 6th edition

Problem Set 4.1 Summary NOTE: THE CALCULATIONS ARE SIMPLY 3-STEP MOLE PROBLEMS, BUT THEY ARE MUCH HARDER THAN MOST YOU’VE DONE BEFORE. (YOU’LL NEED TO WRITE BALANCED EQUATIONS FOR MOST OF THEM.)


Stoichiometry Flow Chart 1. Identify Reaction Type 2. Write a balanced Equation 3. Calculate moles of reactants Given

Æ V & M: Æ Mass:

n=M•V n = g/MM

4. Determine Limiting Reagent 5. Calculate moles of products


Go back to pg. 3 of note packet

Quantitative Analysis Quantitative analysis – the determination of how much of a given component is present in a sample Titration – a process in which one reagent is added to another (usually acids and bases) with which it reacts. An indicator is used to determine the point @ which equivalent quantities of the two reagents have been added. Equivalence point – point @ which just enough titrant has been added to fully react with B. end point – the point during a titration where an indicator turns color Jodi Grack; Wayzata High School; Images from ex. Phenolphthalein Zumdahl Chemistry 6th edition

Quantitative Analysis Ex. 30.0 mL of fruit juice is titrated with 14.85

mL of an NaOH solution which contains 1.82 mg/mL. Determine the mg of vitamin C, C6H8O6, per milliliter of juice.


Solution Stoichiometry Examples: MH+V H+= M OH-VOH1.

When aqueous solutions of sodium hydroxide and Iron (III) nitrate are mixed, a red gelatinous precipitate forms. Calculate the mass of precipitate formed when 50.00 mL of 0.200 M NaOH and 30.00 mL of 0.125 M Fe(NO3)3 are mixed.


Solution Stoichiometry Examples: 2.

Barium Hydroxide reacts with acetic acid, HC2H3O2. Calculate the concentration of all ions and molecules except H2O after the reaction if 75.00 mL of 0.0200 M Ba(OH)2 is added to 22.68 mL of 0.500 M HC2H3O2. (Assume the final is the sum of the initial volumes.)


Solution Stoichiometry Examples: 3. What volume of 0.0720 M AlCl3 is needed to

react fully with 25.0 mL of 0.364 M Pb(NO3)2?


Solution Stoichiometry Examples: 4. 30.0 mL of acetic acid, CH3COOH, is titrated

with 14.22 mL of LiOH. The LiOH solution is 1.42 mg/mL. Determine the mg of the acid per mL of solution.
