Dr. S. M. Condren Chapter 5 Reactions in Aqueous Solutions
Mar 26, 2015
Dr. S. M. Condren
Chapter 5
Reactions
in
Aqueous Solutions
Dr. S. M. Condren
Many reactions involve ionic compounds, Many reactions involve ionic compounds, especially reactions in water — especially reactions in water —
aqueous solutions.aqueous solutions.KMnOKMnO44 in water in water KK++(aq) + MnO(aq) + MnO44
--(aq)(aq)
Reactions in Aqueous Solution
Dr. S. M. Condren
An Ionic Compound, CuCl2, in Water
CCR, page 177CCR, page 177
Dr. S. M. Condren
How do we know ions are How do we know ions are present in aqueous present in aqueous solutions?solutions?
The solutions The solutions conduct electricity!
They are called They are called ELECTROLYTES
HCl, CuClHCl, CuCl22, and NaCl are , and NaCl are strong electrolytes. . They dissociate completely They dissociate completely (or nearly so) into ions.(or nearly so) into ions.
Aqueous Solutions
Dr. S. M. Condren
HCl, CuClHCl, CuCl22, and NaCl are , and NaCl are strong electrolytes.. They dissociate They dissociate completely (or nearly so) into ions.completely (or nearly so) into ions.
Aqueous Solutions
Dr. S. M. Condren
Aqueous SolutionsAcetic acid ionizes only to a small extent, so Acetic acid ionizes only to a small extent, so
it is a it is a weak electrolyte..CHCH33COCO22H(aq)H(aq) ---> ---> CHCH33COCO22
--(aq) + H(aq) + H++(aq)(aq)
Dr. S. M. Condren
Aqueous SolutionsAcetic acid ionizes only Acetic acid ionizes only
to a small extent, so it to a small extent, so it
is a is a weak electrolyte.
CHCH33COCO22H(aq)H(aq) ---> --->
CHCH33COCO22--(aq) + H(aq) + H++(aq)(aq)
Dr. S. M. Condren
Aqueous SolutionsSome compounds Some compounds
dissolve in water but dissolve in water but do not conduct do not conduct electricity. They are electricity. They are called called nonelectrolytes.
Examples include:Examples include:sugarsugarethanolethanolethylene glycolethylene glycol
Examples include:Examples include:sugarsugarethanolethanolethylene glycolethylene glycol
Dr. S. M. Condren
Electrolytes
• Conduct electricity in solution due to the presence of ions
• Strong electrolyte – completely ionized in solution
• Weak electrolyte – partially ionized in solution
• Non-electrolyte – nonionic solution
Dr. S. M. Condren
Solubility Rules
1. All nitrates (NO3-1) are soluble.
2. All compounds of Group IA metals and the ammonium ion, NH4
+, are soluble.
3. All chlorides are soluble except: AgCl, Hg2Cl2 and PbCl2.
4. All sulfates are soluble except: PbSO4, BaSO4, and SrSO4.
Dr. S. M. Condren
Solubility Rules
5. All hydroxides (OH-1)and sulfides (S-2)are insoluble except those of the Group IA metals and the ammonium ion.
6. All carbonates (CO3-2) and phosphates
(PO4-3) are insoluble except those of the
Group IA metals and the ammonium ion.
Dr. S. M. Condren
Net Ionic Equation
Balanced Chemical Equation
Pb(NO3)2 + Na2SO4 ---> PbSO4 + 2NaNO3
Total Ionic Equation
Pb+2 + 2NO3-1 + 2Na+1 + SO4
-2
2Na+ + 2NO3 -1 + PbSO4
Net Ionic Equation
Pb+2 + SO4-2 PbSO4
Dr. S. M. Condren
A solution of Ba(NO3)2 is added to a solution of Na2SO4 to make a precipitate. From a table of solubility rules, the product is
barium sulfate, sodium nitrate
Dr. S. M. Condren
Types of Reactions
• synthesis reactions or combination reactions
• decomposition reactions
• precipitation reactions
• neutralization reactions– acid– base
• oxidation-reduction reaction
Dr. S. M. Condren
Synthesis or Combination Reactions
Formation of a compound from simpler compounds or elements.
2Na(s) + Cl2(g) 2 NaCl(s)
Dr. S. M. Condren
Decomposition Reactions
Separation into constituents by chemical reaction.
catalysis2 H2O2 (aq) 2H2O(l) + O2(g)
Dr. S. M. Condren
Precipitation Reactions
The process of separating a substance from a solution as a solid.
AgNO3 + NaCl ---> AgCl + NaNO3
precipitate
Total Ionic EquationAg+1
(aq) + NO3(aq)-1 + Na(aq)
+1 + Cl(aq)-1 AgCl(s) + NO3(aq)
-1 + Na(aq)+1
Net Ionic Equation
Ag+1(aq) + Cl(aq)
-1 AgCl(s)
Dr. S. M. Condren
Neutralization Reactions
acid + base ---> “salt” + water
Balanced Chemical Equation
HCl + NaOH ---> NaCl + H2O
Total Ionic Equation
H+1 + Cl-1 + Na+1 + OH-1 Na+ + Cl-1 + H2O
Net Ionic Equation
H+1 + OH-1 H2O
Dr. S. M. Condren
Neutralization Reactions
acid + base ---> “salt” + water
Balanced Chemical Equation
H2SO4 + 2KOH ---> K2SO4 + 2H2O
Total Ionic Equation
2H+ + SO4-2 + 2K+ + 2OH-1 2H2O + SO4
-2 + 2K+
Net Ionic Equation
2H+1 + 2OH-1 2H2O
Dr. S. M. Condren
Neutralization Reactions
• acid
• base
• salt
Household acids and Bases
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Neutralization Reactions
• acid– Any of a large class of sour-tasting
substances whose aqueous solutions are capable of turning blue litmus indicators red, of reacting with and dissolving certain metals to form salts, and of reacting with bases or alkalis to form salts.
– Substance that donates H+ ions to solution
Dr. S. M. Condren
An acid -------> HAn acid -------> H++ in water in waterAn acid -------> HAn acid -------> H++ in water in water
Some Some strongstrong acids areacids are
HClHCl hydrochlorichydrochloric
HH22SOSO44 sulfuricsulfuric
HClOHClO44 perchloricperchloric
HNOHNO33 nitricnitric HNOHNO33
ACIDS
Dr. S. M. Condren
WEAK ACIDS = weak WEAK ACIDS = weak electrolyteselectrolytes
CHCH33COCO22HH acetic acidacetic acid
HH22COCO33 carbonic acidcarbonic acid
HH33POPO44 phosphoric acidphosphoric acid
HFHF hydrofluoric acidhydrofluoric acid
Acetic acid
Weak Acids
Dr. S. M. Condren
Nonmetal oxides can be acidsNonmetal oxides can be acids
COCO22(aq) + H(aq) + H22O(liq) O(liq)
---> H---> H22COCO33(aq)(aq)
SOSO33(aq) + H(aq) + H22O(liq) O(liq)
---> H---> H22SOSO44(aq)(aq)
and can come from burning coal and can come from burning coal and oil.and oil.
ACIDS
Dr. S. M. Condren
Neutralization Reactions
• base– Any of a large class of compounds, including
the hydroxides and oxides of metals, having a bitter taste, a slippery solution, the ability to turn litmus blue, and the ability to react with acids to form salts.
– Substance that donates a OH-1 ion to solution
Dr. S. M. Condren
Base ---> OHBase ---> OH-- in water in waterBase ---> OHBase ---> OH-- in water in water
NaOHNaOH(aq)(aq) Na Na++(aq)(aq) + OH + OH--
(aq)(aq)
NaOH is a strong base
BASES
Dr. S. M. Condren
Ammonia, NH3
An Important Base
Dr. S. M. Condren
Neutralization Reactions
• salt– The term salt is also applied to substances
produced by the reaction of an acid with a base, known as a neutralization reaction.
– Salts are characterized by ionic bonds, relatively high melting points, electrical conductivity when melted or when in solution, and a crystalline structure when in the solid state.
Dr. S. M. Condren
pH Scale
@ -2 -----> @ +16
pH = - log [H3O+]
[H3O+] = -antilog pH = 10-pH
For log problems, only decimal places are significant, and all decimal places count
Dr. S. M. Condren
Example: What is the pH of a 1.0 M solution of HCl?pH = - log [H3O+]
[H3O+] = MHCl = 1.0 M
• because it is a strong electrolyte
pH = -log(1.0) = 0.002 significant figures
Dr. S. M. Condren
Example: What is the pH of a 1.0 M solution of HCl?pH = - log [H3O+]
[H3O+] = MHCl = 1.0 M
• because it is a strong electrolyte
pH = -log(1.0) = 0.002 SF
Dr. S. M. Condren
Example: What is the pH of a 0.010 M solution of HCl?
pH = - log [H3O+]
[H3O+] = MHCl = 0.010 M
• because it is a strong electrolyte
pH = -log(0.010) = 2.002 SF
Dr. S. M. Condren
Example: What is the pH of a 2.0 M solution of HCl?
pH = - log [H3O+]
[H3O+] = MHCl = 2.0 M
• because it is a strong electrolyte
pH = -log(2.0) = -0.302 SF
Dr. S. M. Condren
Example: What is the [H3O+] of a solution that has a pH = 2.30? [H3O+] = -antilog pH = 10-pH
[H3O+] = 10-pH = 10-2.30 = 5.0x10-3M2 SF 2 SF
decimal point pacement
Dr. S. M. Condren
pH Scale
Dr. S. M. Condren
Indicators
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Oxidation-Reduction Reaction
Oxidation - loss of electrons
Reduction - gain of electrons
Redox reaction
oxidizing agent - substance that causes oxidation
reducing agent - substance that cause reduction
Dr. S. M. Condren
Identify the oxidizing agent in the reaction:
2Al(s) + 6 H+ ==> 2 Al3+
(aq) + 3 H2(g)
Al, H+, Al3+, H2
Identify the oxidizing agent in the reaction:
Dr. S. M. Condren
Redox Reactions
CuSO4(aq) + Zn(s) Cu(s) + ZnSO4(aq)
4 Al(s) + 3 O2(g) 2 Al2O3(s)
2HgO2HgO(s)(s) 2 Hg 2 Hg(l)(l) + O + O2(g)2(g)
2 Al2 Al(s)(s) + 3 Br + 3 Br2 (l)2 (l) Al Al22BrBr6 (s)6 (s)
Fe2O3(s) + 2 Al(s) 2 Fe(l) + Al2O3(s)
Dr. S. M. Condren
Solution
Solutions, in chemistry, homogeneous mixtures of two or more substances.
Dr. S. M. Condren
Solute
The substance that is present in smallest quantity is said to be dissolved and is called the solute. The solute can be either a gas, a liquid, or a solid.
Dr. S. M. Condren
Solvent
The substance present in largest quantity usually is called the solvent. The solvent can be either a liquid or a solid.
Dr. S. M. Condren
Preparing a Solution
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Preparing a Solution by Dilution
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Molarity
The number of moles of solute per liter of solution.
molarity => M moles of soluteM = -------------------- liter of solution
units => molar = moles/liter = M
Dr. S. M. Condren
Example: A sample of NaNO3 weighing 0.38g is placed in a 50.0-mL volumetric flask. The flask is then filled with water to the mark on the neck, dissolving the solid. What is the molarity of the resulting solution?
M =(0.38g NaNO3)(50.0-mL soln)
= 0.089 mol/L = 0.089 molar = 0.089 M
Dr. S. M. Condren
Stoichiometric Roadmap
Gramsof A
Molesof A
Molesof B
Gramsof B
mol A x (mol B/mol A)Multiply by the
stoichiometric factor
mol B x (g B/mol B)Multiply by the
molar mass
Volumesolution B
g B x (mol A/g A)Divide by themolar mass
Volumesolution A
Vol A x (mol A/L A)Multiply by molarity
Mol B x (L B/mol B)Diviide by molarity
Dr. S. M. Condren
Example: What mass of Na2CO3, in grams, is required for complete reaction with 50.0mL of 0.125 M HNO3?
Na2CO3(aq) + 2 HNO3(aq) 2 NaNO`3(aq) + CO2(g) + H2O(l)
#g Na2CO3 = (50.0 mL)
= 0.331 g Na2CO3
Dr. S. M. Condren
EXAMPLE: Lye, which is sodium hydroxide, can be neutralized by sulfuric acid. How many milliliters of 0.200 M H2SO4 are needed to react completely with 25.0 mL of 0.400 M NaOH?
2 NaOH(aq) + H2SO4(aq) -----> Na2SO4(aq) + 2 H2O
(25.0 mL NaOH) #mL H2SO4 = ----------------------
(0.400 mol NaOH) ------------------------- (1 L NaOH)
(1 L)--------------(1000 mL)
(1 mol H2SO4) -------------------(2 mol NaOH)
(1000 mL H2SO4) ------------------------(0.200 mol H2SO4)
= 25.0 mL H2SO4