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Chapter 4 Aqueous Reactions and Solution Stoichiometry Pg 105
Aqueous Solutions -Aqueous Solutions are solutions that have water as the dissolving medium. -Many reactions contain substances that have been dissolved in water, making them aqueous solutions. donkistry.tripod.com/Chem.jpg
3 Main Major Chemical Reaction Types Involving Aqueous Solutions Precipitation Reactions Acid-Base Reactions Redox Reactions
4.1 General Properties of Aqueous Solutions Solutions are homogeneous mixtures Usually has more solvent than solute. Solute is the substance being dissolved in the solvent
Electrolytic Properties Pure water is a bad conductor The presence of Ions in water makes it into a good conductor Aqueous solution that conduct electricity such as NaCl (aq) or other ionic compounds are electrolyte. Solutions that do not form ions like sucrose and other molecular compounds are nonelectrolytes.
Ionic Compounds in Water Ionic compounds dissolve in water dissociating into component ions (ex. NaCl -> Na + &Cl - ) The polar nature of water makes it a very effective solvent The polarity helps prevent anions and cations from rejoining.
Molecular Compounds in Water Structure usually remains unchanged, they usually do not form ions Acids and a few other compounds like ammonia react with water forming ions making an electrolyte. Ex. HCl make H + and Cl - ions
Strong & Weak Electrolytes Strong Electrolytes = Most ionic compounds and a few molecular compounds. Weak Electrolytes = Molecular compounds that produce few ions when dissolved If the chemical reaction goes both ways, breaking into ions, and recombining, than the substance is a weak electrolyte.
HCl (aq) --> H + + Cl - One arrow means strong electrolyte HC 2 H 3 O 29(aq) H + + C 2 H 3 O 2 - Double arrow means weak electrolyte
4.2 Precipitation Reactions Precipitation Reaction = Reactions that result in the formation of an insoluble product. Precipitate = Insoluble solid formed by a reaction in a solution
Solubility Guidelines for Ionic Compounds Solubility = Amount of substance that can be dissolved in given amount of solvent If less than.01 mol dissolves in a liter, substance is insoluble. In these substances intermolecular attraction is stronger than the waters polarity. Table 4.1 pg 111 (Solubility Guidelines for Common Ionic Compounds in Water) All ionic compounds with 1A elements or ammonia ions are soluble in water.
Is Sodium Carbonate Soluble (Na 2 CO 3 ) Yes. Carbonate is usually insoluble, but when paired with a 1A element, Sodium, the compound becomes soluble.
Exchange (Metathesis) Reactions Exchange or Metathesis Reaction = AX+BY --> AY+BX Precipitation and Acid Base Reactions conform to this pattern
What precipitate forms when BaCl 2 and K 2 SO 4 are mixed? BaSO 4, SO 4 2- is soluble but Ba 2+ is not
Ionic Equations Molecular Equation = complete chemical formulas of reactants and products Complete Ionic Equation = All Soluble strong Electrolytes are shown as ions Spectator ions = ions that are present in the same form on both product and reactant side. These are dropped out to form a Net Ionic Equation.
Steps to Write a Net Ionic Equation Write a balanced Molecular Equation Rewrite to show ions that are formed during dissociation or ionization, only the strong electrolytes are written in ionic form Cancel spectator ions on both sides
Write the net ionic equation for the mixing of CaCl 2 and Na 2 CO 3 CaCl 2(aq) + Na 2 CO 3(aq) --> CaCO 3(S) + 2NaCl (aq) Ca Cl - + 2Na + + CO >CaCO 3(s) + 2Na + + 2Cl - Ca 2+ (aq) + CO 3 2- (aq) -->CaCO 3(s)
Acid-Base Reactions Acids and Bases are common Electrolytes Are some of the most common compounds we encounter
Acids Substances that ionize in aqueous solutions upping H + concentration Protic refers to amount of H + ions ionizing. Monoprotic = 1, Diprotic = 2. Diprotic Acid ionization occurs in two steps, One hydrogen is separated at a time.
Bases Substances that accept H + ions, or increases OH - concentration. Does not need to have an OH - ion, if accepts H + like NH 3 (ammonia is a weak electrolyte)
Strong and Weak Acids and Bases Strong Acids and Bases are strong electrolytes that completely ionize in solutions Weak Acids and Bases are electrolytes that partly ionize in solutions Table 4.2 pg 115 (Common Strong Acids and Bases)
Identifying Strong and Weak Electrolytes Is the compound ionic, yes -> probably strong electrolyte Not ionic, is it an acid Yes, is an acid, if strong, is a strong electrolyte if weak, is a weak electrolyte. Not an acid, is it NH 3 or another molecular base, yes -> weak base, no -> probably nonelectrolyte
Classify HNO 3 as a strong, weak, or non Electrolyte Strong HNO 3 is a strong acid making it a strong electrolyte. mls.jpl.nasa.gov/images/HNO3.jpg
Neutralization Reactions and Salts When acid and base react together, it is a neutralization reaction. These reactions form a salt and a water. Salt = any ionic compound whose cation comes form a base and anion comes from an acid.
Write the net ionic equation for HC 2 H 3 O 2 and Ba(OH) 2 HC 2 H 3 O 2(aq) +OH - (aq) --> H 2 O (l) + C 2 H 3 O 2 - (aq)
Acid-Base Reaction with Gas Formation The sulfide ion and carbonate ion react with acids to form gases 2HCl (aq) + Na 2 S (aq) --> H 2 S (g) +2NaCl (aq) HCl (aq) +NaHCO 3(aq) -->NaCl (aq) + H 2 O (l) +CO 2(g)
4.4 Oxidation - Reduction Reactions
Oxidation and Reduction Metals undergoing erosion are losing electrons and forming cations Loss of electrons is known as oxidization The gain of electrons by a substance is called reduction
Oxidation Numbers Oxidization number is the actual charge of the of the atom. In elemental form the Oxidization number is 0 Oxidization of monatomic ions equals the charge Nonmetals are usually negative, Oxygen usually is -2, Hydrogen is +1, Fluorine is -1. Sum of oxidation numbers in neutral compound is 0 or equal to the charge in a polyatomic ion.
Determine the oxidation stat of sulfur in H 2 S -2, Hydrogen is always +1 2H = +2 so S = -2 so that sum of oxidation numbers = 0
Oxidation of Metals by Acids and Salts Displacement Reactions = ion is solution is displaced or replaced through the oxidation of an element. A+BX-->AX+B
Write the net ionic equation for the reaction of aluminum and hydrobromic acid 2Al (S) + 6H + (aq) +6Br - -->2Al 3+ (aq) +6Br - (aq) +3H 2(g) 2Al (s) +6H + (aq) -->2Al 3+ +3H 2(g)
The Activity Series Table 4.5 pg 124 Activity Series of Metals in Aqueous Solution Is a table of metals arranged in order of decreasing ease of oxidation. Alkali and Alkaline Earth Metals are at the top. Metals on the list can be oxidized by any of the ions below them.
Can Pb(NO 3 ) 2 can oxidize Zn, Cu, or Fe Zn and Fe Refer to table 4.5
4.5 Concentrations Of Solutions Concentration = Amount of solute dissolved in a given quantity of solvent or solution.
Molarity Molarity (M) = (moles of solute)/(Volume of Solution in Liters)
Calculate the molarity of a solution made by dissolving 23.4 g of sodium sulfate in enough water to form 125ml of solution 23.4g*(1mol Na 2 SO 4 /142g Na 2 SO 4 ) =.165 mols 125ml*(1L/1000ml)=.125 .165mols Na 2 SO 4 /.125L = 1.32M
Dilution Adding water to lower the concentration is called dilution M i *V i =M f *V f i = initial f = final M = Molarity V= Volume
How many mL of 3.0 M H 2 SO 4 are required to make 450 mL of.10 M H 2 SO 4 ? V i = (M f V f )/M i ((.10M)(450mL))/3.0M = 15 mL
4.6 Stoichiometry and Chemical Analysis
Titrations Second solution of known concentration is called the standard solution Combining the standard solution with a solution of unknown concentration to get a chemical reaction is called titration Equivalence point is where equivalent quantities have been brought together indicators change the color helping us to find this point. If molar ratio is 1 to 1 you may use the dilution equation. If not, convert standard solution to mols, then use molar ratio to give you the mols of the unknown, then convert to grams.
How many grams of chloride ion are in the sample of the water if 20.2 mL of.1 M Ag is required to react with all the chloride in the sample? (20.2 mL solution) * (1L/1000mL solution) * (.1mol Ag + /L solution) = 2.02 * 1mol Ag + : 1mol Cl - (2.02*10 -3 mol Cl - ) * (35.5g Cl - /1 mol Cl - ) = 7.17 * g Cl -