BIG IDEA TWO October 13, 2016
Topics to Cover in Big Idea 2 1. Ionic, metallic, and covalent bonds 2. Polarity and dipole moment 3. Intermolecular forces (IMF): 4. Lewis dot structures 5. Resonance forms 6. Incomplete octets 7. Expanded octets 8. Formal charge 9. Molecular geometry (VSEPR) 10. Bonding and phases 11. Kinetic molecular theory 12. The ideal gas equation 13. Dalton s Law 14. Deviations from the ideal behavior 15. Density 16. Solutions: molarity and mole fraction
TYPES OF REACTIONS & SOLUTION STOICHIOMETRY
Review: Aqueous Solutions 1. Solute 2. Solvent 3. Solubility à Water is the universal solvent Does everything always dissolve in water? 4. Electrolytes Strong electrolytes Weak electrolytes Nonelectrolytes
Composition of Solutions Molarity (M) = moles solute/liters of solution Ex: A 500.0-g sample of potassium phosphate is dissolved in enough water to make 750 ml of solution.
Composition of Solutions Give the concentration of ions in a solution of 0.50 M Co(NO 3 ) 2 Calculate the number of moles in 2.5 L of the Co(NO 3 ) 2 solution.
Composition of Solutions Which of the following solutions contains the greatest number of ions? a) 400.0 ml of 0.10 M NaCl. b) 300.0 ml of 0.10 M CaCl 2. c) 200.0 ml of 0.10 M FeCl 3. d) 800.0 ml of 0.10 M sucrose.
Composition of Solutions: Dilutions The process of adding water to a concentrated or stock solution to achieve the molarity desired for a particular solution. Dilution with water does not alter the numbers of moles of solute present. Moles of solute before dilution = moles of solute after dilution M 1 V 1 = M 2 V 2
Composition of Solutions: Dilutions Ex: What is the minimum volume of a 2.00 M NaOH solution needed to make 150.0 ml of a 0.800 M NaOH solution?
Types of Chemical Reactions (Rxns) 1. Synthesis 2. Decomposition 3. Single Replacement 4. Double Replacement Precipitation Reactions 5. Combustion Reactions 6. Acid Base Reactions 7. Oxidation Reduction Reactions
Writing different reactions Steps for writing reactions: 1. Identify the type of reaction 2. Predict the product(s) using the type of reaction as a model 3. Balance the reaction
Type 1: Synthesis Rxn Synthesis reactions occur when two substances (generally elements) combine and form a compound. reactant + reactant à 1 product Rxn Outline: A + B à AB Example: 2H 2 + O 2 à 2H 2 O
Type 2: Decomposition Rxn Decomposition reactions occur when a compound breaks up into the elements or into simpler compounds 1 Reactant à Product + Product Rxn Outline: AB à A + B Example: 2 H 2 O à 2H 2 + O 2
Decomposition Exceptions Carbonates and chlorates are special case decomposition reactions that do not go to the elements. Carbonates (CO 3 2- ) decompose to carbon dioxide and a metal oxide Example: CaCO 3 à CO 2 + CaO Chlorates (ClO 3- ) decompose to oxygen gas and a metal chloride Example: 2 Al(ClO 3 ) 3 à 2 AlCl 3 + 9 O 2
Type 3: Single Replacement Single Replacement rxns occur when one element replaces another in a compound. A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-). Element + Compoundà Element + Compound A + BC à AC + B (if A is a metal) OR A + BC à BA + C (if A is a nonmetal) (remember the cation always goes first!)
Type 4: Double Replacement Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound Compound + compound à compound+ compound AB + CD à AD + CB
Precipitation Reaction A double displacement reaction in which a solid forms and separates from the solution. When ionic compounds dissolve in water, the resulting solution contains the separated ions. Precipitate the solid that forms.
Precipitation Reaction Soluble solid dissolves in solution; (aq) is used in reaction. Insoluble solid does not dissolve in solution; (s) is used in reaction. Insoluble and slightly soluble are often used interchangeably.
Solubility Rules (In Your Handbook) 1. Most nitrate (NO 3- ) salts are soluble. 2. Most alkali metal (group 1A) salts and NH 4 + are soluble. 3. Most Cl -, Br -, and I - salts are soluble (except Ag +, Pb 2+, Hg 2 2+ ). 4. Most sulfate salts are soluble (except BaSO 4, PbSO 4, Hg 2 SO 4, CaSO 4 ). 5. Most OH - are only slightly soluble (NaOH, KOH are soluble, Ba(OH) 2, Ca(OH) 2 are marginally soluble). 6. Most S 2-, CO 3 2-, CrO 4 2-, PO 4 3- - salts are only slightly soluble, except for those containing the cations in Rule 2.
Writing PPT Rxns Total Ionic Equation Represents as ions all reactants and products that are strong electrolytes. Net Ionic Equation Includes only those solution components undergoing a change.
PPT Rxn Example Write the correct formula equation, complete ionic equation, and net ionic equation for the reaction between cobalt(ii) chloride and sodium hydroxide.
Stoichiometry of PPT Rxns 1. Identify the species present in the combined solution, and determine what reaction if any occurs. 2. Write the balanced net ionic equation for the reaction. 3. Calculate the moles of reactants. 4. Determine which reactant is limiting. 5. Calculate the moles of product(s), as required. 6. Convert to grams or other units, as required.
Stoichiometry of PPT Rxns 10.0 ml of a 0.30 M sodium phosphate solution reacts with 20.0 ml of a 0.20 M lead(ii) nitrate solution (assume no volume change). What precipitate will form? What mass of precipitate will form?
Stoichiometry of PPT Rxns 10.0 ml of a 0.30 M sodium phosphate solution reacts with 20.0 ml of a 0.20 M lead(ii) nitrate solution (assume no volume change). What is the concentration of nitrate ions left in solution after the reaction is complete?
Reaction Type Summary
Type 5: Combustion Rxns Combustion reactions occur when a hydrocarbon reacts with oxygen gas. This is also called burning. In order to burn something you need the 3 things 1. A Fuel (hydrocarbon) 2. Oxygen to burn it with 3. Something to ignite the reaction (spark)
Type 6: Acid Base Reactions Acid proton donor Base proton acceptor For a strong acid and base reaction: NaOH (aq) + HCl (aq) à NaCl (aq) + H 2 O (l) H + (aq) + OH (aq) à H 2 O(l)
Type 7: Redox Reactions Reactions in which one or more electrons are transferred. An oxidation occurs when an atom or ion loses electrons. A reduction occurs when an atom or ion gains electrons. LEO the lion goes GER
Redox Characteristics Oxidation is loss of electrons Reduction is gain of electrons Oxidation is always accompanied by reduction The total number of electrons is kept constant Oxidizing agents oxidize and are themselves reduced Reducing agents reduce and are themselves oxidized
KNOW & MEMORIZE! Oxidizing agent Is itself reduced Gains electrons Causes oxidation Reducing agent Is itself oxidized Loses electrons Causes reduction
Assigning Oxidation Numbers 1. Oxidation state of an atom in an element = 0 2. Oxidation state of monatomic ion = charge of the ion 3. Oxygen = -2 in covalent compounds (except in peroxides where it = -1) 4. Hydrogen = +1 in covalent compounds 5. Fluorine = -1 in compounds 6. Sum of oxidation states = 0 in compounds 7. Sum of oxidation states = charge of the ion in ions
Practice Problems What is the oxidation number of... 1) N in NO 3 2) C in CO 32 3) Cr in CrO 42 4) Cr in Cr 2 O 72
Ox-Reduction Problems Determine which element is oxidized and which is reduced when lithium reacts with nitrogen to form lithium nitride. 6 Li(s) + N 2 (g) à 2 Li 3 N(s)
The Role of Oxidation Numbers in Oxidation-Reduction Reactions Chemists eventually extended the idea of oxidation and reduction to reactions that do not formally involve the transfer of electrons. CO(g) + H2O(g) à CO2(g) + H2(g) What changes in this reaction is the oxidation state of these atoms. The oxidation state of carbon increases from +2 to +4, while the oxidation state of the hydrogen decreases from +1 to 0.
Practice Problem 2: Determine which atom is oxidized and which is reduced in the following reaction Sr(s) + 2 H 2 O(l) à Sr 2+ (aq) + 2 OH - (aq) + H 2 (g)
Practice Problem 3: Determine which element is oxidized and which is reduced when lithium reacts with nitrogen to form lithium nitride.
BALANCING OX-RED RXNS
What is a Half-Reaction? A half-reaction is simply one which shows either reduction OR oxidation, but not both: Ag + + Cu à Ag + Cu 2+ It has BOTH a reduction and an oxidation in it. That is why we call it a redox reaction, from REDuction and OXidation.
What you must be able to do is look at a redox reaction and separate out the two half-reactions in it. To do that, identify the atoms which get reduced and get oxidized. Here are the two half reactions from the example: Ag + + Cu à Ag + Cu 2+ Ag + à Ag Cu à Cu 2+
When you look at the two half-reactions, you will see they are already balanced for atoms with one Ag on each side and one Cu on each side. So, all we need to do is balance the charge. To the silver half-reaction, we add one electron: Ag + + e à Ag To the copper half-reaction, we add two electrons: Cu à Cu 2+ + 2e
Balance each half-reaction for atoms and charge: 1. Cl 2 àcl 2. Sn àsn 2+ 3. Fe 2+ àfe 3+ 4. Sn + NO 3 àsno 2 + NO 2 5. HClO + Co à Cl 2 + Co 2+
Balancing in an acidic solution: H 2 O: water is present because the reaction is taking place in solution H + : the hydrogen ion is available because it is in acid solution e - : electrons are available because that's what is transferred in redox reactions All three will be used in balancing the equation.
1. Balance the atom being reduced/oxidized. In our example, there is already one Mn on each side of the arrow, so this step is already done. MnO 4 à Mn 2+ 2. Balance the oxygens. Do this by adding water molecules (as many as are needed) to the side needing oxygen. In our case, the left side has 4 oxygens, while the right side has none, so: MnO 4 àmn 2+ + 4H 2 O
3. Balance the hydrogens. Do this by adding hydrogen ions (as many as are needed) to the side needing hydrogen. In our example, we need 8 (notice the water molecule's formula, then consider 4 x 2 = 8). 8H + + MnO 4 à Mn 2+ + 4H 2 O 4. Balance the total charge. This will be done using electrons. It is ALWAYS the last step. 5e + 8H + + MnO 4 à Mn 2+ + 4H 2 O
Example: Cr 2 O 72 à Cr 3+ 1. Balance the atom being reduced/ oxidized. 2. Balance the oxygens. 3. Balance the hydrogens. 4. Balance the total charge.
Practice Problems 1. Re àreo 2 2. Cl 2 àhclo 3. NO 3 àhno 2 4. H 2 GeO 3 àge 5. H 2 SeO 3 àseo 42
There are three other chemical species available in a basic solution: 1. H 2 O: water is present because the reaction is taking place in solution 2. OH - : the hydroxide ion is available because it is in basic solution 3. e - : electrons are available because that's what is transferred in redox reactions.
PbO 2 à PbO Step One to Four: Balance the half-reaction AS IF it were in acid solution. 1. Balance the atom being reduced/oxidized. 2. Balance the oxygens (using H 2 O). 3. Balance the hydrogens (using H + ). 4. Balance the charge. When you do that to the above half-reaction, you get: 2e + 2H + + PbO 2 àpbo + H 2 O
Step Five: Convert all H + to H 2 O. Do this by adding OH ions to both sides. The side with the H + will determine how many hydroxide to add. In our case, the left side has 2 hydrogen ions, while the right side has none, so: 2e + 2H + + PbO 2 àpbo + H 2 O 2e + 2H 2 O + PbO 2 à PbO + H 2 O + 2OH
Step Six: Remove any duplicate molecules or ions. In our example, there are two water molecules on the left and one on the right. This means one water molecule may be removed from each side, giving: 2e + H 2 O + PbO 2 à PbO + 2OH