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Aqueous Reactions
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
This is a reaction in which reactants are in solution
Solution – homogeneous mixture composed of two parts:solute – the medium which is dissolvedsolvent – the medium which dissolves the solute.
Molarity (M)Unit of concentration, moles of solute per liter
of solution.
solutionofLiters
soluteofMolesMolarity
Solutions
Example: What is the molarity(M) of a solution which contains 17.51g of NaCl in 751mL of solution?
F.W. (NaCl): 58.45g/mol
Solution volume
molmolg
gNaClmoles 2996.0
/45.58
51.17
LmL
LmLsolutionofLiters 751.0
1000
1751
Solutions
Example: What is the molarity (M) of a solution which contains 17.51g of NaCl in 751mL of solution?
M
L
molmolarity
399.0
751.0
2996.0
Solutions
Example: What volume of 6.00M NaOH is required to make 500mL of 0.100M NaOH?
Mconcentrated = 6.00M Mdilute = 0.100MVconcentrated = ? Vdilute = 500mL
0.100M(500mL) = 6.00M(Vconcentrated)
Vconcentrated = 8.33mL
SolutionsSolutionsDilution
Some compounds conduct electricity when dissolved in water – electrolytes
Those compounds which do not conduct electricity when dissolved in water are called – nonelectrolytes
Properties of SolutesProperties of SolutesCompounds in Water
Some compounds conduct electricity when dissolved in water – electrolytes
Those compounds which do not conduct electricity when dissolved in water are called – nonelectrolytes
Properties of SolutesProperties of SolutesCompounds in Water
The conductivity of the solution is due to the formation of ions when the compound dissolves in water
These ions are not the result of a chemical reaction, they are the result of a dissociation of the molecule into ions that compose the solid.
Properties of SolutesProperties of Solutes
)()()( 2 aqClaqNasNaCl OH
Ionic Compounds in Water (Electrolytes)
In this case no ions are formed, the molecules just disperse throughout the solvent.
Properties of SolutesProperties of Solutes
)()( 2 aqsugarssugar OH
Molecular Compounds in Water (Nonelectrolytes)
There are exceptions to this, some molecules are strongly attracted to water and will react with it.
Properties of SolutesProperties of SolutesMolecular Compounds in Water(Nonelectrolytes)
There are exceptions to this, some molecules are strongly attracted to water and will react with it.
Properties of SolutesProperties of Solutes
ClOHOHHCl
OHNHOHNH
32
423
Molecular Compounds in Water (Nonelectrolytes)
Strong electrolytes – A substance which completely ionizes in water.
For example:
Properties of SolutesProperties of Solutes
ClOHOHHCl 32
Strong and Weak Electrolytes
Weak electrolyte: A substance which partially ionizes when dissolved in water.
For example:
Notice that the arrow in this reaction has two heads, this indicates that two opposing reactions are occurring simultaneously.
Properties of SolutesProperties of Solutes
OHCOCHOHHCOCH 323223
Strong and Weak Electrolytes
Since both reactions occur at the same time, this is called a chemical equilibrium
Properties of SolutesProperties of Solutes
OHHCOCHOHCOCH
and
OHCOCHOHHCOCH
223323
323223
Strong and Weak Electrolytes
Acid - substance which ionizes to form hydrogen cations (H+) in solution Examples:
Hydrochloric Acid HCl Nitric Acid HNO3
Acetic Acid CH3CO2HSulfuric Acid H2SO4
Notice that sulfuric acid can provide two H+’s – Diprotic acid,
the other acids can provide only one H+ – Monoprotic acid.
Acids, Bases, and SaltsAcids, Bases, and Salts
Bases - substances which reacts with H+ ions formed by acids.
Examples: ammonia NH3
sodium hydroxide NaOH
Acids, Bases, and SaltsAcids, Bases, and SaltsBases
H+ + OH- H2O
- Metal hydroxides (NaOH for example) provide OH- by disassociation.
- Bases like ammonia make OH- by reacting with water (ionization)
NH3 + H2O NH4+ + OH-
Acids, Bases, and SaltsAcids, Bases, and SaltsAcid-Base Reactions
- The strength of acids and bases are concerned with the The strength of acids and bases are concerned with the ionization (or dissociation) of the substance, ionization (or dissociation) of the substance, notnot its its chemical reactivity.chemical reactivity.
Example:Example:Hydrofluoric acid (HF) is a weak acid, but it is very Hydrofluoric acid (HF) is a weak acid, but it is very chemically reactive.chemically reactive.- this substance can’t be stored in glass bottles because - this substance can’t be stored in glass bottles because it reacts with glass (silicon dioxide).it reacts with glass (silicon dioxide).
Acids, Bases, and SaltsAcids, Bases, and SaltsStrong Acids
Common Strong AcidsCommon Strong AcidsHydrochloric AcidHydrochloric Acid HCl HCl Hydrobromic AcidHydrobromic Acid HBrHBrHydroiodic acidHydroiodic acid HIHINitric AcidNitric Acid HNOHNO33
Perchloric AcidPerchloric Acid HClOHClO44
Chloric AcidChloric Acid HClOHClO33
Sulfuric AcidSulfuric Acid HH22SOSO44
Acids, Bases, and SaltsAcids, Bases, and SaltsCommon Strong Acids and Bases
Common Strong BasesCommon Strong BasesLithium HydroxideLithium Hydroxide LiOHLiOHSodium HydroxideSodium Hydroxide NaOHNaOHPotassium HydroxidePotassium Hydroxide KOHKOHRubidium HydroxideRubidium Hydroxide RbOHRbOHCesium HydroxideCesium Hydroxide CsOHCsOHCalcium HydroxideCalcium Hydroxide Ca(OH)Ca(OH)22
Strontium HydroxideStrontium Hydroxide Sr(OH)Sr(OH)22
Barium HydroxideBarium Hydroxide Ba(OH)Ba(OH)22
Acids, Bases, and SaltsAcids, Bases, and SaltsCommon Strong Acids and Bases
- Reaction between an acid and a base.
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
“The reaction between an acid and a metal hydroxide produces water and a salt”
Salt – an ionic compound whose cation comes from a base and anion from an acid.
Acids, Bases, and SaltsAcids, Bases, and SaltsNeutralization Reaction
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
- despite the appearance of the equation, the reaction actually takes place between the ions.
Acids, Bases, and SaltsAcids, Bases, and SaltsNeutralization Reaction
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
Total Ionic EquationH+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)
H2O(l) + Na+(aq) + Cl-
(aq)
Acids, Bases, and SaltsAcids, Bases, and SaltsNeutralization Reaction
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
Total Ionic EquationH+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)
H2O(l) + Na+(aq) + Cl-
(aq)
Some of the ions appear unchanged in both the reactants and products – spectator ion
Acids, Bases, and SaltsAcids, Bases, and SaltsNeutralization Reaction
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
Total Ionic EquationH+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)
H2O(l) + Na+(aq) + Cl-
(aq)
Net Ionic EquationH+(aq) + OH-(aq) H2O(l)
Acids, Bases, and SaltsAcids, Bases, and SaltsNeutralization Reaction
AX + BY AY + BX
Three driving forces for the reaction: - Formation of an insoluble solid (precipitation reaction)- Formation of a weak electrolyte or nonelectrolyte- Formation of a gas that escapes from solution
Metathesis ReactionsMetathesis Reactions
- A reaction which forms a solid (precipitate)
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
- AgCl is classified as an insoluble substance
Solubility – amount of substance that can be dissolved in a specific amount of water (g/L or mg/L)
- for this textbook, any substance with a solubility less than 0.01mol/L is considered insoluble.
Metathesis ReactionsMetathesis ReactionsPrecipitation Reaction
Solubility Guidelines for Ionic Compounds
Metathesis ReactionsMetathesis Reactions
1. Most nitrates (NO3-) and acetates (CH3CO2
-) are soluble in water.
2. All chlorides are soluble except: Hg+, Ag+, Pb2+, Cu+
3. All sulfates are soluble except: Sr2+, Ba2+, Pb2+
4. Carbonates (CO32-), Phosphates (PO4
3-), Borates (BO33-),
Arsenates (AsO43-), and Arsenites (AsO3
3-) are insoluble.5. Hydroxides (OH-) of group Ia and Ba2+ and Sr2+ are soluble.6. Most sulfides (S2-) are insoluble.
Reactions Which Form Weak and Non-electrolytes
Metathesis ReactionsMetathesis Reactions
- One example of this type of reaction is a neutralization reaction.
Mg(OH)2 + 2 HCl MgCl2 + 2 H2O
- Insoluble metal oxide (base) and a strong acid.
MgO(s) + 2 HCl(aq) MgCl2(aq) + H2O(l)
Reactions Which Form Gases
Metathesis ReactionsMetathesis Reactions
- Carbonates and Hydrogen Carbonates decompose to give CO2
- Carbonate and Acid2 HCl(aq) + Na2CO3(aq) 2 NaCl(aq) + CO2(g) + H2O(l)
- Hydrogen Carbonate and AcidHCl(aq) + NaHCO3(aq) NaCl(aq) + CO2(g) + H2O(l)
Oxidation-Reduction Reactions- reaction where electrons are exchanged.
2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g)
Na(s) Na+(aq) + 1 e-
oxidation – loss of electrons
2 H+(g) + 2 e- H2(g)
reduction – gain of electrons
Oxidation-Reduction ReactionsOxidation-Reduction Reactions
- Oxidation of metals by acids to form saltsMg(s) + 2HCl(aq) MgCl2(aq) + H2(g)
- Oxidation of metals saltsFe(s) + Ni2+(aq) Fe2+(aq) + Ni(s)
Notice that the Fe is oxidized to Fe2+ and the Ni2+ is reduced to Ni.
Oxidation-Reduction ReactionsOxidation-Reduction Reactions
- Oxidation of metals by acids to form saltsMg(s) + 2HCl(aq) MgCl2(aq) + H2(g)
- Oxidation of metals saltsFe(s) + Ni2+(aq) Fe2+(aq) + Ni(s)
but,Fe2+(aq) + Ni(s) no reaction
Oxidation-Reduction ReactionsOxidation-Reduction Reactions
- Some metals are more easily oxidized than others.- The relative ability of an element to be oxidized is
summarized in a table.
Activity series - a list of metals arranged in decreasing ease of oxidation.
- The higher the metal on the activity series, the more active that metal.
- Any metal can be oxidized by the ions of elements below it.
The Activity Series
Solution StoichiometrySolution Stoichiometry
- We can now use molarity to determine stoichiometric quantities.
ExampleHow many grams of hydrogen gas are produced when 20.0 mL of 1.75M HCl is allowed to react with 15.0g of sodium metal?
2 HCl(aq) + 2 Na(s) H2(g) + 2 NaCl(aq)