5 Oct. 2010

5 Oct. 2010

Objective: SWBAT describe properties of an aqueous solution, and write an equation for a precipitation reaction.

Do now: What is an electrolyte? Describe why it exhibits the properties of an electrolyte.

Agenda

I. Do nowII. Aqueous solutions notesIII. Precipitation Reaction practice

problemsHomework: p. 160 #1-6, 8-14 evens

(JR)p. 161 #15, 18-24 evens (TTL)

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

solvent: the part of a solution doing the dissolving, present in larger amount

solute: a substance being dissolved, present in a smaller amount

solution: homogeneous mixture of two or more substances SOLUTE

SOLVENTSOLUTIONSOLUTION

Examples

KCl in water? Carbon dioxide in water? Alcohol in water?

Now: only solutions in which the solvent is water, and the solute is a liquid or a solid.

Properties of an Aqueous Solution

Are either electrolytes or nonelectrolytes

Electrolyte: a substance that, when dissolved in water, results in a solution that can conduct electricity. ex: NaCl dissolved in water: solid

NaCl dissociates into Na+ and Cl- ions Nonelectrolyte: does not conduct

electricity when dissolved in water. ex: pure water

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.

7 Oct. 2010

Objective: SWBAT define and describe acids and bases as Arrhenius or Bronsted, and as strong or weak.

Do now: Soluble or insoluble? (try first without using your chart!)a. Ca3(PO4)2

b. Mn(OH)2

c. AgClO3

d. K2S

Agenda

I. Homework check (ELS)II. Acids and Bases: Definitions, strong

and weakIII. Neutralization ReactionsHomework: p. 161 #26, 27, 28, 29, 30,

32, 34 (JMS)Read p. 135-145 and do practice

exercises a-d on p. 145

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) + SO42-(aq)

Triprotic: 3 H+

Strong vs. Weak Acids

HCl hydrochloric HBr hydrobromic HI hyroiodic HNO3 nitric H2SO4 sulfuric HClO4 perchloric

HF hydrofluoric HNO2 nitrous H3PO4 phosphoric CH3COOH acetic

Strong Acids

Dissociate 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)

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

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)

Homework

p. 161 #26, 27, 28, 29, 30, 32, 34 (JMS)

Bring your book to class!

13 October 2010

Objective: SWBAT 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: Write balanced molecular, ionic and net ionic equations for this reaction between a weak acid and a strong base: H3PO4(aq) + Ba(OH)2(aq)

Agenda

I. Do nowII. Read objective, debrief do now, review

agendaIII. Homework presentationIV. Notes: Writing redox half reactions and

assigning oxidation numbersV. Practice problemsVI. Discussion of types of redox reactions (p.

139-145)Homework: p. 162 #37, 40, 43, 44, 45, 47, 50,

54, 55 (PD), read p. 139-145

14 October 2010

Objective: SWBAT 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: Write and label (ox. or red.) the two half-reactions:

Cu(s) + 2AgNO3(aq) Cu(NO3)2 (aq) + 2Ag(s)

Agenda

I. Do nowII. Read objective, debrief do now, review

agendaIII. Homework presentationIV. Notes: Writing redox half reactions and

assigning oxidation numbersV. Practice problemsVI. Discussion of types of redox reactions (p.

139-145)Homework: p. 162 #37, 40, 43, 44, 45, 47, 50,

54, 55 (PD), read p. 139-145

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?

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. Li2O

b. 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) 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)

KNaLiCaMgAlZnFeNiSnPbHCuHgAgAu

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 #37, 40, 43, 44, 45, 47, 50, 54, 55 (PD)

14 Oct. 2010

Objective: SWBAT determine, from worked out examples, the process by which to solve molarity, dilution and gravimetric analysis problems.

Do now: For the following metal displacement reactions, determine if a reaction will occur. If yes, write the products:

Fe + CuSO4 Ni + NaCl Li + ZnCO3 Al + CuCl2

KNaLiCaMgAlZnFeNiSnPbHCuHgAgAu

Agenda

Do now, homework

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 two examples (dilutions) and the final two (gravimetric analysis)

Then, solve the example problems on the back using your problem solving steps.