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29 September 2011
Objective: You will be able to: predict the products of and write
net ionic equations for precipitation reactions
work on the chapter 3 problem set
Agenda
I. Precipitation ReactionsI. Predicting productsII. Writing ionic equations and net ionic
equationsII. Practice ProblemsIII. Chapter 3 Problem Set Work TimeHomework: Test TuesdayChapter 3 problem set: TuesdayChapter 4 Notes: Thursday
You will be able to write and balance molecular, ionic and net ionic equations and predict the solubility of products.
Reactions in Aqueous Solutions
Introduction
Most chemical reactions and virtually all biological processes take place in water!
Three categories of reactions in aqueous solutions: Precipitation reactions Acid-Base reactions Redox reactions
Strong vs. Weak Electrolytes
Strong: Solute is 100% dissociated in water
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf
Why is water good at hydrating ions?
)()()( 2 aqClaqNasNaCl OH
Acids and bases are electrolytes: Some are strong:
Some are weak and ionize incompletely:
Double arrow indicates a reversible reaction: reaction can occur in both directions
)()()( 2 aqClaqHgHCl OH
)()()( 33 aqHaqCOOCHaqCOOHCH
Reversible Reaction
Molecules ionize and then recombine
Until ionization is occurring as fast as recombination: chemical equilibrium
Precipitation Reactions
formation of an insoluble product (precipitate) which separates from the solution.
This is also an example of a double displacement reaction
)(2)()(2)()( 3223 aqKNOsPbIaqKIaqNOPb
Solubility
How do you predict whether a precipitate will form?
Depends on the solubility of the solute p. 125-126
Examples: FeCO3 KCl AgCl
Practice Determining Solubility
1. Ag2SO4
2. CaCO3
3. Na3PO4
4. CuS5. Ca(OH)2
6. Zn(NO3)2
Writing Equations
We don’t always write the entire chemical equation as if each species existed as a complete molecule This doesn’t really reflect what’s
actually happening!
Molecular Equations
Written as though all species existed as molecules or whole units.
Doesn’t always reflect reality. What’s actually happening?
Dissolved ionic compounds dissociate into ions!!
)(2)()(2)()( 3223 aqKNOsPbIaqKIaqNOPb
Ionic Equation
Shows dissolved species as free ions. Notice that there are ions that show
up on both sides of the equation. Spectator ions They can be eliminated.
)(2)(2)(
)(2)(2)(2)(
32
32
aqNOaqKsPbI
aqIaqKaqNOaqPb
Net Ionic Equation
To give this net ionic equation showing species that actually take place in the reaction:
)(2)(2)(
)(2)(2)(2)(
32
32
aqNOaqKsPbI
aqIaqKaqNOaqPb
)()(2)( 22 sPbIaqIaqPb
Example 1
Solutions of barium chloride and sodium sulfate react to produce a white solid of barium sulfate and a solution of sodium chloride.
Example 2
A potassium phosphate solution is mixed with a calcium nitrate solution. Write a net ionic equation.
Example 3
Solutions of aluminum nitrate and sodium hydroxide are mixed. Write the net ionic equation for the reaction.
Homework
Test Tuesday Chapter 3 problem set: Tuesday Chapter 4 Notes: Friday
5 October 2011
Objective: You will be able to: determine the identity of an unknown
alkaline earth metal carbonate, M2CO3, using gravimetric analysis.
In your lab notebook: Write a balanced molecular equation
for the reaction between solutions of a group 2 metal (M2+) carbonate and calcium chloride.
Agenda
I. Do nowII. Copper (II) sulfate hydrate lab…III. Determining the formula of a metal
carbonate by gravimetric analysis pre-lab
Homework: Be sure your procedure is in your notebook, ready for lab tomorrow!
Determining the formula of M2CO3
Put the green cards in order. Place the blue cards under each step
for which you need those materials. Have me check it when you think
you’ve completed the procedure in the correct order.
Copy the steps, including detail about use of the materials to accomplish each step, into your lab notebook.
3 October 2011
Objective: You will be able to: write net ionic equations that
predict the products of and describe acid-base reactions
Do now: Find the mass of your precipitate
+ filter paper(s), record, and put it in the drying oven.
Agenda
I. Do nowII. Acid-Base Reactions Notes and
ProblemsIII. Find mass of precipitate againHomework: p. 160 #2, 3, 7, 9, 12,
17, 19, 22, 24a, 30, 31, 33: due tomorrow
Acid-Base Reactions
Properties of Acids and Bases
Arrhenius definition: Acids: ionize in water to produce
H+ ions Bases: ionize in water to produce
OH- ions
Acids
React with metals like Zn, Mg, Fe to produce hydrogen gas2HCl(aq) + Mg(s) MgCl2(aq) + H2(g)
React with carbonates and bicarbonates to produce CO2(g)2HCl(aq) + CaCO3(s) CaCl2(aq) + H2O(l) + CO2(g)HCl(aq) + NaHCO3(s) NaCl(aq) + H2O(l) + CO2(g)
Brønsted Definition Acid: proton donor Base: proton acceptor don’t need to be aqueous!
HCl(aq) H+(aq) + Cl-(aq)
proton
But…
HCl(aq) H+(aq) + Cl-(aq) H+ is very attracted to the negative
pole (O atom) in H2O HCl(aq) + H2O(l) H3O+(aq) + Cl-
(aq) H3O+ : hydronium ion Above, a Brønsted acid (HCl)
donates a proton to a Brønsted base (H2O)
Types of Acids
Monoprotic: each one yields one hydrogen ion upon ionization Ex: HCl, HNO3, CH3COOH,
Diprotic: each gives two H+ ions Ex: H2SO4
H2SO4(aq) H+(aq) + HSO4-(aq)
HSO4-(aq) > H+(aq) + SO4
2-(aq) Triprotic: 3 H+
Strong vs. Weak Acids
HCl hydrochloric HBr hydrobromic HI hydroiodic HNO3 nitric H2SO4 sulfuric HClO3 chloric HClO4 perchloric
HF hydrofluoric HNO2 nitrous H3PO4 phosphoric CH3COOH acetic
Strong AcidsDissociate completely
Weak AcidsDissociate Incompletely
Brønsted Bases
H+(aq) + OH-(aq) H2O(l) Here, the hydroxide ion accepts a
proton to form water. OH- is a Brønsted base.
NH3(aq) + H2O(l) NH4+(aq) + OH-
(aq)
13 October 2011
Take Out Homework Objective: You will be able to:
write net ionic equations that predict the products of and describe acid-base reactions
Homework Quiz: Week of 10/12a. You have a solution of sodium chloride and want to precipitate out the chloride ions. What ionic compound can you add?b. Write the molecular and net ionic equations for this reaction.
Agenda
I. Homework QuizII. Check HomeworkIII. Acid-Base Reactions Notes and
ExamplesIV. Practice ProblemsHomework: p. 161 #30, 31, 33;
worksheet 1-3: due MondayLab calculations: Monday
Brønsted Acid or Base?
a. HBrb. NO2
-
c. HCO3-
d. SO42-
e. HI
Acid-Base Neutralization
reaction between an acid and a base produce water and a salt salt: ionic compound (not including
H+ or OH- or O2-) acid + base water + salt
Strong acid + Strong base example HCl(aq) + NaOH(aq) NaCl(aq) +
H2O(l) Write the ionic and net ionic
equations! Which are spectator ions?
Weak acid + Strong base example: HCN(aq) + NaOH(aq) NaCN(aq) +
H2O(l)HCN does not ionize completely
HCN(aq) + Na+(aq) + OH-(aq) Na+(aq) + CN-(aq) +
H2O(l) Write the net ionic equation
Write equations
a. CH3COOH(aq) + KOH(aq)
b. H2CO3(aq) + NaOH(aq)
c. HNO3(aq) + Ba(OH)2(aq)
17 October 2011
Take Out Lab Notebook Objective: You will be able to:
Predict the products of and write net ionic equations for acid-base reactions producing gases.
Homework Quiz: (Week of Oct. 17) Write the net ionic equation for the
reaction of solutions of carbonic acid and sodium hydroxide.
Agenda
I. Homework QuizII. Acid-Base reactions that produce gases
Examples and problemsIII. Practice ProblemsIV. Redox reactionsHomework: Quiz tomorrow(one precip, one strong acid-strong base,
one weak acid-strong base, one acid-salt producing gas)
Acid-Base Reaction: Gas Formation
Some salts (with CO32-, SO3
2-, S2-, HCO3-)
react with acids to form gaseous products
Na2CO3(aq) + 2HCl(aq) 2NaCl(aq) + H2CO3(aq)
Then the carbonic acid breaks down:H2CO3(aq) H2O(l) + CO2(g)
Practice Problems
a. NaHCO3(aq) + HCl(aq)
b. Na2SO3(aq) + HCl(aq)
c. K2S (aq) + HCl(aq)
Practice Problems Worksheet
18 October 2010
Objective: You will be able to: model the transfer of electrons between
reactants in redox reactions by correctly writing oxidation and reduction half reactions and overall reactions; determine oxidation numbers.
Do now: Review the strong acids and gases formed by the reaction of salts with acids (5 min.)
Agenda
I. Do nowII. Writing equations quizIII. Redox equations – differentiating
between oxidation and reduction half reactions.
Homework: Review p. 135-145: tomorrow
Quiz – 25 min.
Oxidation-Reduction Reactions
What was being transferred in acid-base reactions? Protons!
Redox reactions: electron transfer!
2Mg(s) + O2(g) 2MgO(s)
Mg2+ bonds with O2-
What’s happening with electrons? Two steps, 2 half reactions:
2Mg 2Mg2+ + 4e-
O2 + 4e- 2O2-
2Mg + O2 + 4e- 2Mg2+ + 202- + 4e-
2Mg + O2 2Mg2+ + 2O2-
2Mg2+ + 2O2- 2MgO
Oxidation: Half reaction that refers to the LOSS of electrons
Reduction: Half reaction that refers to the GAIN of electrons 2Mg 2Mg2+ + 4e-
O2 + 4e- 2O2-
Reducing agent: donates electrons Oxidizing agent: accepts electrons
Another Example
Zn(s) + CuSO4(aq) ZnSO4(aq) + Cu(s)
(What type of reaction?) For which elements is the charge
different as a reactant and a product?
19 October 2011
Objective: You will be able to: write redox half reactions determine oxidation number for
elements in a compound classify types of redox reactions
Do now: On your packet from yesterday, write the two half reactions and label oxidation and reduction for the reaction:Fe(s) + 2HCl(aq) → FeCl2(aq) + H2(g)
Agenda
I. Objective/AgendaII. Redox ReviewIII. Notes and ExamplesIV. Practice ProblemsHomework: p. 162 #40, 43, 45, 47,
49, 51, 54, 55
Oxidation Numbers
Keeps track of electrons in redox reactions
The number of charges the atom would have in a molecule (or ionic compound) if electrons were transferred completely.
Assigning Oxidation Numbers
Free elements = 0 (ex: H2, Na, K, O2) Monotomic ions = charge of ion (ex:
Li+ = +1, Fe3+ = +3) Oxygen = -2 (peroxide O2
2- = -1) Hydrogen = +1, except with metals
in binary compounds (ex: LiH) then = -1
Fluorine = -1 In a neutral molecule, sum must = 0 Not always integers
Examples
a. Li2Ob. HNO3
c. Cr2O72-
d. PF3
e. SO2
f. MnO4-
4 Types of Redox Reactions
Combination S(s) + O2(g) SO2(g)
Decomposition 2HgO(s) 2Hg(l) + O2(g)
Combustion C3H8(g) + 5O2(g) 3CO2(g) +
4H2O(l) Displacement
Three types…
Three types of displacement
Hydrogen displacement With alkali metals and some alkaline earth metals
and cold water or HCl 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) Zn(s) + 2HCl(aq) ZnCl2(aq) H2(g)
Metal displacement (use activity series) TiCl4(g) + 2Mg(l) Ti(s) + 2MgCl2(l)
Halogen displacement F2>Cl2>Br2>I2 (moves down group 17) Cl2(g) + 2KBr(aq) 2KCl(aq) + Br2(l)
Classify and Write Oxidation #s
a. 2N2O(g) 2N2(g) + O2(g)b. 6Li(s) + N2(g) 2Li3N(s)c. Ni(s) + Pb(NO3)2(aq) Pb(s) + Ni(NO3)2(aq)d. 2NO2(g) + H2O(l) HNO2(aq) + HNO3(aq)e. Fe + H2SO4 FeSO4 + H2
f. S + 3F2 SF6
g. 2CuCl Cu + CuCl2
h. 2Ag + PtCl2 2AgCl + Pt
Homework
p. 162 #40, 43, 45, 47, 49, 51, 54, 55
Unit 2 Problem Set
3 and 4 only
24 October 2011 Objective: You will be able to:
determine a procedure for three calculations relating to reactions in aqueous solutions and use these to solve problems.
Homework Quiz: Week of Oct. 24 Classify the following reactions as
precipitation, acid-base (or acid-salt) or redox.
If redox, specify which type of reaction, write two half reactions, and identify which is oxidation and which is reduction.
a. 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)b. Na2CO3(aq) + 2HCl(aq) → 2NaCl + H2O(l) + CO2(g)
Agenda
I. Unit 2 Problem Set #3 and 4II. Problem solving: Reactions in
aqueous solutionsHomework: p. 163 #61, 65, 69, 73,
77, 79: Mon.Unit 2 Test: Thurs.Unit 3 starts tomorrow!
Determining problem solving processes from examples
With a partner, examine the first two examples for calculating molarity.
Determine and write out the steps to solve these problems.
Repeat for the second example (dilutions) and the final example (gravimetric analysis)
Then, solve the example problems on the back using your problem solving steps.
Concentration
Calculate the molarity of 29.0 g of ethanol (C2H5OH) in 545 mL of solution.
Calculate the volume in mL of a solution required to provide 2.14 g of sodium chloride from a 0.270 M solution.
Dilution
Describe how to prepare 1.00 L of 0.646 M HCl solution, starting with a 2.00 M HCl solution.
Gravimetric Analysis
A sample of 0.6760 g of an unknown compound containing barium ions is dissolved in water and treated with an excess of Na2SO4. If the mass of the BaSO4 precipitate formed is 0.4105 g, what is the percent by mass of Ba in the original unknown compound?
Homework
p. 163 #61, 65, 69, 73, 77, 79: Tues. Unit 2 Test: Thurs.