29 september 2011

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.