Ch. 4 Patterns of Ch. 4 Patterns of Chemical Reactivity Chemical Reactivity Demo: Pour together two clear Demo: Pour together two clear colorless liquids colorless liquids Did a chemical reaction occur? Did a chemical reaction occur? How do you know? How do you know? Demo: AlkaSeltzer in water, Demo: AlkaSeltzer in water, or calcium in water or calcium in water Did a chemical reaction occur? Did a chemical reaction occur? 04m13vd1 04m13vd1
69
Embed
1 Ch. 4 Patterns of Chemical Reactivity lDemo: Pour together two clear colorless liquids lDid a chemical reaction occur? How do you know? lDemo: AlkaSeltzer.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
11
Ch. 4 Patterns of Chemical Ch. 4 Patterns of Chemical ReactivityReactivity
Ch. 4 Patterns of Chemical Ch. 4 Patterns of Chemical ReactivityReactivity
Demo: Pour together two clear colorless Demo: Pour together two clear colorless liquidsliquids
Did a chemical reaction occur?Did a chemical reaction occur?How do you know?How do you know?
Demo: AlkaSeltzer in water, Demo: AlkaSeltzer in water, or calcium in wateror calcium in water
Did a chemical reaction occur?Did a chemical reaction occur?
04m13vd104m13vd1
22
Observing and Predicting Reactions
Observing and Predicting Reactions
How do we know whether a reaction How do we know whether a reaction occurs? What clues does nature offer? occurs? What clues does nature offer? Make a list.Make a list.
Review photos of reactionsReview photos of reactions
Building DemolitionBuilding Demolition Whale RemovalWhale Removal return
1717
OdorOdor
Certain molecules, especially Certain molecules, especially those containing sulfur or those containing sulfur or nitrogen, have distinctive nitrogen, have distinctive odors.odors.
returnreturn
1818
Electrical ConductivityElectrical Conductivity
Ba(OH)Ba(OH)22 + H + H22SOSO44
returnreturn
1919
Density/VolumeDensity/Volume
Sugar + HSugar + H22SOSO44
returnreturn
2020
pH ChangepH Change
returnreturn
2121
Magnetic PropertiesMagnetic Properties
Fe + SFe + S88
2222
Generate ElectricityGenerate Electricity
Chemical Chemical reaction reaction in the in the batterybattery
returnreturn
2323
4.4 Observing and Predicting Reaction Patterns
4.4 Observing and Predicting Reaction Patterns
Predictions: Predictions: do an experimentdo an experiment use periodicityuse periodicity use classifications of use classifications of
reactions involve the reactions involve the reaction of an element reaction of an element or a compound with or a compound with oxygen, usually with oxygen, usually with the evolution of heatthe evolution of heat
2424
In the following particulate In the following particulate representations, a circle represents an representations, a circle represents an atom and different circles represent atom and different circles represent different elements. Using these different elements. Using these representations, draw pictures of all representations, draw pictures of all the different types of atomic/molecular the different types of atomic/molecular changes these substances could changes these substances could undergo.undergo.
Precipitation reactions: (An example of a Precipitation reactions: (An example of a "double replacement" or "metathesis" "double replacement" or "metathesis" reaction).reaction).
Precipitation Reactions form a solid when Precipitation Reactions form a solid when two solutions are combined. two solutions are combined.
An example is the combining aqueous An example is the combining aqueous potassium chromate with aqueous lead potassium chromate with aqueous lead nitrate to form the precipitate lead nitrate to form the precipitate lead chromate (still used in school bus paint!!)chromate (still used in school bus paint!!)
3232
Describing Reactions in Solution
Describing Reactions in Solution
To identify the precipitate or predict the To identify the precipitate or predict the formation of a precipitate the solubilities of formation of a precipitate the solubilities of compounds can be used. These rules should compounds can be used. These rules should already be memorized!already be memorized!
Table 4.1, pg 144Table 4.1, pg 144
3333
Solubility PrinciplesSolubility Principles
Most nitrate and acetate salts are soluble.Most nitrate and acetate salts are soluble.Most salts containing the alkali metal ions Most salts containing the alkali metal ions
(Li(Li++, Na, Na++, K, K++, Cs, Cs++, Rb, Rb++) and the ammonium ) and the ammonium ion (NHion (NH44
++) are soluble.) are soluble.
Most chloride, bromide and iodide salts are Most chloride, bromide and iodide salts are soluble. Notable exceptions are salts soluble. Notable exceptions are salts containing the ions Agcontaining the ions Ag++, Pb, Pb2+2+ and Hg and Hg22
2+2+..
3434
Solubility PrinciplesSolubility Principles
Most sulfate salts are soluble. Notable exceptions are Most sulfate salts are soluble. Notable exceptions are BaSOBaSO44, PbSO, PbSO44, HgSO, HgSO44 and CaSO and CaSO44..
Most hydroxide salts are only slightly soluble. Most hydroxide salts are only slightly soluble. Important soluble hydroxides are NaOH and KOH. Important soluble hydroxides are NaOH and KOH. Ca(OH)Ca(OH)22, Sr(OH), Sr(OH)22, and Ba(OH), and Ba(OH)22 are somewhat soluble*. are somewhat soluble*.
Most sulfide, carbonate, chromate, and phosphate salts Most sulfide, carbonate, chromate, and phosphate salts are only slightly soluble**.are only slightly soluble**.
* Note Group 2 trends : As you go down the group sulfate solubility decreases * Note Group 2 trends : As you go down the group sulfate solubility decreases and hydroxide solubility increases.and hydroxide solubility increases.
** Slightly soluble compounds will form precipitates using "normal" ** Slightly soluble compounds will form precipitates using "normal" concentrations.concentrations.
3535
Describing Reactions in Solution
Describing Reactions in Solution
For reactions involving ionic compounds, we For reactions involving ionic compounds, we can write the reaction as a can write the reaction as a molecular molecular equationequation (or formula equation). This shows (or formula equation). This shows the normal (complete) formulas of all the normal (complete) formulas of all compounds:compounds:
We can rewrite the same reaction as a We can rewrite the same reaction as a complete complete ionic equationionic equation - Shows a picture of all that - Shows a picture of all that actually occurs in solutionactually occurs in solution
strong electrolytes represented as ions in solutionstrong electrolytes represented as ions in solution weak and non- electrolytes still written in molecular weak and non- electrolytes still written in molecular
A A net ionic equationnet ionic equation includes only the includes only the solution components involved in the solution components involved in the reaction (spectator ions, which do not reaction (spectator ions, which do not undergo change, are omitted)undergo change, are omitted)
Stoichiometry of Precipitation Reactions – Stoichiometry of Precipitation Reactions – based on Chapter 3 stoichiometry concepts, based on Chapter 3 stoichiometry concepts, but using molarity (concentration) but using molarity (concentration) relationships.relationships.Practice with Chapter 3 & Molarity!Practice with Chapter 3 & Molarity!Sample: How many grams of lead(II) Sample: How many grams of lead(II)
hydroxide can be formed when 22.5 mL of hydroxide can be formed when 22.5 mL of 0.135 M Pb(NO0.135 M Pb(NO33))22 solution reacts with excess solution reacts with excess sodium hydroxide? (Hint: Use a BCA table).sodium hydroxide? (Hint: Use a BCA table).
3939
Acid-Base ReactionsAcid-Base Reactions
Definitions:Definitions:Arrhenius:Arrhenius:
Acid - forms Acid - forms HH++ ions in solution (e.g HCl) ions in solution (e.g HCl)Base - forms Base - forms OHOH-- ions in solution (e.g. NaOH) ions in solution (e.g. NaOH)
net ionic equation: Hnet ionic equation: H++ (aq) + OH (aq) + OH-- (aq) (aq) H H22O (l)O (l)
4141
Acid-Base TitrationsAcid-Base Titrations
Acid-base titrations (volumetric analysis) – Acid-base titrations (volumetric analysis) – determine an unknown quantity through titration.determine an unknown quantity through titration. Titration involves adding a precisely measured volume Titration involves adding a precisely measured volume
of a solution of known concentration (the titrant) into a of a solution of known concentration (the titrant) into a solution containing the substance being analyzed (the solution containing the substance being analyzed (the analyte).analyte).
The titrant reacts with the analyte in a known manner, The titrant reacts with the analyte in a known manner, such as an acid-base reaction.such as an acid-base reaction.
4242
Acid-Base TitrationsAcid-Base Titrations
An indicator marks the equivalence point (or An indicator marks the equivalence point (or stoichiometric point) where just the right amount stoichiometric point) where just the right amount of titrant has been added to completely react with of titrant has been added to completely react with the analyte. the analyte.
The endpoint is where the indicator actually The endpoint is where the indicator actually changes color, which hopefully occurs near the changes color, which hopefully occurs near the equivalence point.equivalence point.
4343
Acid-Base ReactionsAcid-Base Reactions
Note the similarities to precipitation Note the similarities to precipitation reactions.reactions.
Acid-Base reactions are another variation Acid-Base reactions are another variation of a double replacement reaction. The key of a double replacement reaction. The key is the production of water.is the production of water.
Other common double replacement Other common double replacement reactions produce gases.reactions produce gases.
4444
Acid-Base StoichiometryAcid-Base Stoichiometry
There are numerous variations on the acid-There are numerous variations on the acid-base reaction. Be sure to read through the base reaction. Be sure to read through the many examples in Section 4.8. We will many examples in Section 4.8. We will consider these examples now from a consider these examples now from a “modeling” perspective.“modeling” perspective.
4545
Acid-Base ReactionsAcid-Base Reactions
You first want to examine the acid-base reaction You first want to examine the acid-base reaction (similar to predicting a precipitation reaction). (similar to predicting a precipitation reaction). Here are some general steps (they can and should Here are some general steps (they can and should vary depending on the problem):vary depending on the problem):
1.1. List the major species present in solution before the List the major species present in solution before the reaction occurs. Decide what reaction will occur (look for reaction occurs. Decide what reaction will occur (look for formation of water or gases)formation of water or gases)
2.2. Write a balanced equation. (leave space for a BCA table) Write a balanced equation. (leave space for a BCA table)
3. Calculate the moles of reactants. For solutions, use the 3. Calculate the moles of reactants. For solutions, use the volumes of the original solutions and their molarities volumes of the original solutions and their molarities (before mixing). Input into a BCA table.(before mixing). Input into a BCA table.
4646
Acid-Base ReactionsAcid-Base Reactions
4.4. Determine the limiting reactant if Determine the limiting reactant if appropriate.appropriate.
5.5. Analyze the problem and find the moles of Analyze the problem and find the moles of reactant or product asked for.reactant or product asked for.
6.6. Convert to grams or volume of solution if Convert to grams or volume of solution if asked forasked for
*All problems are different. Don’t “force” a *All problems are different. Don’t “force” a problem into a particular solution method.problem into a particular solution method.
element + cmpd element + cmpd cmpd + element cmpd + element(The more metallic element in the compound (The more metallic element in the compound is displaced.)is displaced.)
carbon + metal oxidescarbon + metal oxides 3C + Fe3C + Fe22OO33 3CO + 2Fe 3CO + 2Fe
reactions in which reactions in which electrons are transferredelectrons are transferredcauses a change in the charge of an ion or of causes a change in the charge of an ion or of
oxidation state of an element in a moleculeoxidation state of an element in a molecule
Oxidation states - Oxidation states - numbersnumbers assigned to assigned to elementselementsused to keep track of used to keep track of electronselectrons (not the same as (not the same as
charge, but related) charge, but related)
6464
Rules for Assigning Oxidation States (Table 4.2)
Rules for Assigning Oxidation States (Table 4.2)
The oxidation state of an uncombined The oxidation state of an uncombined element is zero (includes diatomic elements element is zero (includes diatomic elements HH22,N,N22, O, O22, F, F22, Cl, Cl22, Br, Br22 and I and I22).).
The oxidation state of a monatomic ion is The oxidation state of a monatomic ion is the same as its charge (e.g. the sulfide ion, the same as its charge (e.g. the sulfide ion, SS2-2-, has an oxidation state of -2)., has an oxidation state of -2).
6565
Rules for Assigning Oxidation States (Table 4.2)
Rules for Assigning Oxidation States (Table 4.2)
Oxygen has an oxidation state of -2 in Oxygen has an oxidation state of -2 in covalent compounds (except in peroxides covalent compounds (except in peroxides (O(O22
2-2-) where each oxygen is assigned an ) where each oxygen is assigned an oxidation state of -1).oxidation state of -1).
In covalent compounds hydrogen is In covalent compounds hydrogen is assigned an oxidation state of +1. assigned an oxidation state of +1. (Hydrogen has a -1 charge in hydrides such (Hydrogen has a -1 charge in hydrides such as lithium hydride (LiH) or sodium hydride as lithium hydride (LiH) or sodium hydride (NaH).(NaH).
6666
Rules for Assigning Oxidation States (Table 4.2)
Rules for Assigning Oxidation States (Table 4.2)
In compounds, fluorine always has an oxidation In compounds, fluorine always has an oxidation state of -1.state of -1.
The sum of the oxidation states of the elements in The sum of the oxidation states of the elements in a neutral compound must equal zero.a neutral compound must equal zero.
The sum of the oxidation states of the elements in The sum of the oxidation states of the elements in a polyatomic ion must equal the charge on the a polyatomic ion must equal the charge on the polyatomic ion.polyatomic ion.
6767
Rules for Assigning Oxidation States (Table 4.2)
Rules for Assigning Oxidation States (Table 4.2)
Oxidation states may be non-integers. For Oxidation states may be non-integers. For
example in iron (III) oxide (Feexample in iron (III) oxide (Fe33OO44), the iron ), the iron
has an oxidation state of 8/3 (eight-thirds). has an oxidation state of 8/3 (eight-thirds).
6868
Rules for assigning oxidation states
Rules for assigning oxidation states
Practice: Identify the oxidation state of Practice: Identify the oxidation state of each atom in the following compounds:each atom in the following compounds:Magnesium nitrateMagnesium nitrateLithium nitrideLithium nitrideSodium nitriteSodium nitrite
6969
Characteristics of Redox Reactions
Characteristics of Redox Reactions
OxidationOxidation
a a lossloss of electrons of electrons
an an increaseincrease in oxidation state in oxidation state
the substance oxidized is the the substance oxidized is the reducing agentreducing agent (gives electrons (gives electrons to another substance)to another substance)
ReductionReduction
a a gaininggaining of electrons of electrons
a a decreasedecrease in oxidation state in oxidation state
the substance reduced is the the substance reduced is the oxidizing agentoxidizing agent (takes electrons (takes electrons away from another substance)away from another substance)
By the half-reaction method :By the half-reaction method : In acidic solutionIn acidic solution1.1. Write separate oxidation and Write separate oxidation and
reduction reduction reactions for the reaction.reactions for the reaction.2.2. For each half reaction :For each half reaction :
balance all the elements balance all the elements except hydrogen and except hydrogen and oxygenoxygen
balance balance oxygenoxygen atoms using H atoms using H22OObalance balance hydrogenhydrogen atoms using H atoms using H++
balance the charge using balance the charge using electronselectrons
3.3. If necessary, balance electrons lost and If necessary, balance electrons lost and gained in each half reaction by gained in each half reaction by
multiplying one or both half reactions multiplying one or both half reactions by an integer.by an integer.
4.4. AddAdd the half-reactions and the half-reactions and cancelcancel out out like species.like species.
5.5. Check to make sure charges and Check to make sure charges and elements are elements are balancedbalanced..
7272
Example 4.19Example 4.19
Potassium dichromate is a bright orange Potassium dichromate is a bright orange compound that can be reduced to a blue-compound that can be reduced to a blue-violet solution of chromium(III) ions. In violet solution of chromium(III) ions. In acidic conditions, potassium dichromate acidic conditions, potassium dichromate reacts with ethyl alcohol as follows:reacts with ethyl alcohol as follows:
In Basic solution (see example 4.20)In Basic solution (see example 4.20)::
1.1. Balance as in an acidic solution (see above).Balance as in an acidic solution (see above).
2.2. Add a number of OH- ions equal to the H+ Add a number of OH- ions equal to the H+ ions present to both sides of each half ions present to both sides of each half
reaction to for Hreaction to for H22O.O.
3.3. Eliminate the number of HEliminate the number of H22O molecules that O molecules that appear on both sides of the equation.appear on both sides of the equation.
4.4. Check to make sure charges and elements Check to make sure charges and elements are balanced.are balanced.
7474
Group (Partner) QuizGroup (Partner) Quiz
1.1. Give the oxidation state of each element in sodium Give the oxidation state of each element in sodium chlorate (NaClOchlorate (NaClO33))
2.2. In the following reaction, identify the oxidizing In the following reaction, identify the oxidizing agent, the reducing agent, the substance being agent, the reducing agent, the substance being oxidized, and the substance being reducedoxidized, and the substance being reduced