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.
Feb 24, 2016
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 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)
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. 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)
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.