chem 101 week 6 pt1
TRANSCRIPT
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CHEM 101
Chapter 4Part 1
Week Ending 2/24/12
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Reactions in Aqueous SolutionChapter 4
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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A solution is a homogenous mixture of 2 or more substances
The solute is(are) the substance(s) present in the smaller amount(s)
The solvent is the substance present in the larger amount
Solution Solvent Solute
Soft drink (l)
Air (g)
Soft Solder (s)
H2O
N2
Pb
Sugar, CO2
O2, Ar, CH4
Snaqueous solutions
of KMnO4
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An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity.
A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity.
nonelectrolyte weak electrolyte strong electrolyte
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Strong Electrolyte – 100% dissociation
NaCl (s) Na+ (aq) + Cl- (aq)H2O
Weak Electrolyte – not completely dissociated
CH3COOH CH3COO- (aq) + H+ (aq)
Conduct electricity in solution?
Cations (+) and Anions (-)
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Ionization of acetic acid
CH3COOH CH3COO- (aq) + H+ (aq)
A reversible reaction. The reaction can occur in both directions.
Acetic acid is a weak electrolyte because its ionization in water is incomplete.
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Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner.
H2O
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Electrolytes
• Substances that dissociate into ions when dissolved in water.
• A nonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so.
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Electrolytes and Nonelectrolytes
Soluble ionic compounds tend to be electrolytes.
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Electrolytes and Nonelectrolytes
Molecular compounds tend to be nonelectrolytes, except for acids and bases.
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Nonelectrolyte does not conduct electricity?
No cations (+) and anions (-) in solution
C6H12O6 (s) C6H12O6 (aq)H2O
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Electrolytes
• A strong electrolyte dissociates completely when dissolved in water.
• A weak electrolyte only dissociates partially when dissolved in water.
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Strong Electrolytes Are…
• Strong acids• Strong bases• Soluble ionic salts
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Acids
There are only seven strong acids:• Hydrochloric (HCl)• Hydrobromic (HBr)• Hydroiodic (HI)• Nitric (HNO3)
• Sulfuric (H2SO4)
• Chloric (HClO3)
• Perchloric (HClO4)
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Properties of Acids
Have a sour taste. Vinegar owes its taste to acetic acid. Citrusfruits contain citric acid.
React with certain metals to produce hydrogen gas.
React with carbonates and bicarbonatesto produce carbon dioxide gas
Cause color changes in plant dyes.
2HCl (aq) + Mg (s) MgCl2 (aq) + H2 (g)
2HCl (aq) + CaCO3 (s) CaCl2 (aq) + CO2 (g) + H2O (l)
Aqueous acid solutions conduct electricity.
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Bases
The strong bases are the soluble salts of hydroxide ion:• Alkali metals• Calcium• Strontium• Barium
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Have a bitter taste.
Feel slippery. Many soaps contain bases.
Properties of Bases
Cause color changes in plant dyes.
Aqueous base solutions conduct electricity.
Examples:
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Arrhenius acid is a substance that produces H+ (H3O+) in water
Arrhenius base is a substance that produces OH- in water
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A Brønsted acid is a proton donorA Brønsted base is a proton acceptor
acidbase acid base
A Brønsted acid must contain at least one ionizable proton!
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Monoprotic acidsHCl H+ + Cl-
HNO3 H+ + NO3-
CH3COOH H+ + CH3COO-
Strong electrolyte, strong acid
Strong electrolyte, strong acid
Weak electrolyte, weak acid
Diprotic acidsH2SO4 H+ + HSO4
-
HSO4- H+ + SO4
2-
Strong electrolyte, strong acid
Weak electrolyte, weak acid
Triprotic acidsH3PO4 H+ + H2PO4
-
H2PO4- H+ + HPO4
2-
HPO42- H+ + PO4
3-
Weak electrolyte, weak acid
Weak electrolyte, weak acid
Weak electrolyte, weak acid
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Identify each of the following species as a Brønsted acid, base, or both. (a) HI, (b) CH3COO-, (c) H2PO4
-
HI (aq) H+ (aq) + I- (aq) Brønsted acid
CH3COO- (aq) + H+ (aq) CH3COOH (aq) Brønsted base
H2PO4- (aq) H+ (aq) + HPO4
2- (aq)
H2PO4- (aq) + H+ (aq) H3PO4 (aq)
Brønsted acid
Brønsted base
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Solution StoichiometryThe concentration of a solution is the amount of solute present in a given quantity of solvent or solution.
M = molarity =moles of solute
liters of solution
What mass of KI is required to make 500. mL of a 2.80 M KI solution?
volume of KI solution moles KI grams KIM KI M KI
500. mL = 232 g KI166 g KI
1 mol KIx
2.80 mol KI
1 L solnx
1 L
1000 mLx
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Preparing a Solution of Known Concentration
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Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution.
DilutionAdd Solvent
Moles of solutebefore dilution (i)
Moles of soluteafter dilution (f)=
MiVi MfVf=
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Other Concentration Terms• Dilute- a solution containing a small amount of solute• Concentrated- a solution containing more soluteSometimes relative concentrations of solutions are
expressed with the following terms:Saturated- solution of x which is in equilibrium with
undissolved xUnsaturated- a solution which contains a lower
concentration of solute than a saturated solutionSupersaturated- unstable situation in which the solution
actually contains more than the equilibrium concentration of solute
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How would you prepare 60.0 mL of 0.200 M HNO3 from a stock solution of 4.00 M HNO3?
MiVi = MfVf
Mi = 4.00 M Mf = 0.200 M Vf = 0.0600 L Vi = ? L
Vi =MfVf
Mi
= 0.200 M x 0.0600 L4.00 M
= 0.00300 L = 3.00 mL
Dilute 3.00 mL of acid with water to a total volume of 60.0 mL.
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Types of Chemical Reactions
1. Precipitation2. Acid-Base3. Oxidation-Reduction-virtually all chemical reactions can be put into one of these classes
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Precipitation Reactions
Precipitate – insoluble solid that separates from solution
molecular equation
ionic equation
net ionic equation
Pb2+ + 2NO3- + 2Na+ + 2I- PbI2 (s) + 2Na+ + 2NO3
-
Na+ and NO3- are spectator ions
PbI2
Pb(NO3)2 (aq) + 2NaI (aq) PbI2 (s) + 2NaNO3 (aq)
precipitate
Pb2+ + 2I- PbI2 (s)
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Precipitation of Lead Iodide
PbI2Pb2+ + 2I- PbI2 (s)
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Writing Net Ionic Equations1. Write the balanced molecular equation.
2. Write the ionic equation showing the strong electrolytes completely dissociated into cations and anions.
3. Cancel the spectator ions on both sides of the ionic equation
4. Check that charges and number of atoms are balanced in the net ionic equation
AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq)
Ag+ + NO3- + Na+ + Cl- AgCl (s) + Na+ + NO3
-
Ag+ + Cl- AgCl (s)
Write the net ionic equation for the reaction of silver nitrate with sodium chloride.