CHAPTER 4Types of Chemical Reactionsand Solution Stoichiometry
Classification of Matter Solutions are homogeneous mixtures
Two kinds of mixtures • Heterogeneous - not uniform in composition Examples???? • Homogeneous–uniform in composition AKA: SOLUTIONS • Alloys–solid solutions that contain different metals and sometimes nonmetallic substances. Can you name any alloys? Ex. Gold jewelry, steel, bronze….
U Homogeneous Mixtures = Solutions Salt in salt water Sugar in soda drinks • Solute – substances being dissolved • Solvent – substance that does the dissolving Carbon dioxide in soda drinks Water in salt water Water in soda V
Homogeneous Mixtures = Solutions CAUTION: Be careful when deciding which is Uand which isV • If U and V are in the same phase… • Uis the lesser amount • V is the greater amount • If U and V are in the different phases… • Uchanges its phase • V retains its phase
O O H H From the nine choices below, which accurately indicates hydrogen bonding of H2O molecules? Why? 1) H-O-H….H-O-H 2) O = O 3) O-H-H-O 4) O = O 5) H-O….H-O 6) H– H– H 7) H….H 8) O – H – O 9) H-O-H-O-H-O-H O O H….H H H V V V H H O O O O
4.1 Water, the “Universal Solvent” Q: What happens when a solid dissolves? Consider the structure of water, a BENT molecule. 105o… NOT linear 180o O-H bond: unequal sharing of electrons… +,- (O is more electronegative than H)
When salts (ionic compounds) dissolve in water, they dissociate into individual cations and anions. NaCl(s) Na+(aq) + Cl-(aq) AgNO3(s) Ag+(aq) + NO3-(aq) MgCl2(s) Mg2+(aq) + 2 Cl-(aq) Na2SO4(s) 2 Na+(aq) + SO42-(aq) AlCl3(s) Al3+(aq) + 3 Cl-(aq)
Q: What happens when a solid dissolves? Consider the structure of water, a BENT molecule. 105o… NOT linear 180o O-H bond: unequal sharing of electrons… +,- (O is more electronegative than H) + end is attracted to the solute’s anion - end is attracted to the solute’s cation A: Strong cation-anion force (bond) replaced by strong water-ion interactions.
General Rule of Solubility/Miscibility “Like Dissolves Like” Molecule classes that are soluble/miscible: • Polar and Ionic………… (H2O and NaCl) • Polar and Polar………… (H2O and HC2H3O2, vinegar) • Nonpolar and Nonpolar………… (grease and soap) H–CH2–CH2–CH2 – H propane Organic compounds that contain only C’s and H’s are nonpolar
TRY: Predict which will mix: NaNO3 and H2O C6H14 and H2O I2 and C6H14 I2 and H2O Ionic and polar… will Hydrocarbon and polar… won’t Nonpolar and hydrocarbon… will Nonpolar and polar… won’t
TRY: Write the dissociation of: NaNO3(s) K2Cr2O7(s) Ba(OH)2(s) Na+(aq) + NO3-(aq) 2K+(aq) + Cr2O7-2(aq) Ba+2(aq) + 2OH-(aq)
4.2 – Nature of Aqueous Solutions, Strong & Weak Electrolytes
Electrolytes vs. Nonelectrolytes The ammeter measures the flow of electrons (current) through the circuit. • If the ammeter measures a current, and the bulb • glows, then the solution conducts. • If the ammeter fails to measure a current, and the • bulb does not glow, the solution is non-conducting.
Definition of Electrolytes and Nonelectrolytes An electrolyte is: • A substance whose aqueous solution conducts • an electric current. A nonelectrolyte is: • A substance whose aqueous solution DOES NOT • conduct an electric current. Try to classify the following substances as electrolytes or nonelectrolytes…
Electrolytes, YES or no? • Pure water…………………………… • Tap water……………………………… • Sugar solution……………………… • Sodium chloride solution…… • Hydrochloric acid solution… • Lactic acid solution……………… • Ethyl alcohol solution…………… • Pure, solid sodium chloride… no YES no YES YES YES no no But why do some compounds conduct electricity in solution while others do not…?
Ions tend to stay in solution where they canconduct a current rather than re-forming a solid. The reason for this is the polar nature of the water molecule… Positive ions associate with the negative end of the water dipole (oxygen). Negative ions associate with the positive end of the water dipole (hydrogen).
“THOU SHALT MEMORIZE THE EIGHT (8) STRONG ACIDS FROM THE “STUFF” WORKSHEET.”… Cooper Strong acids completely ionize in solution. 3 2
“THOU SHALT MEMORIZE THE STRONG BASES FROM THE “STUFF” WORKSHEET.”… Cooper Group I hydroxides and CBS hydroxides
Most covalent compounds do not ionizeat all in solution. Sugar (sucrose – C12H22O11), and ethanol (ethyl alcohol – C2H5OH) do not ionize - That is why they are nonelectrolytes!
Solubility • maximum grams of solute that will dissolve in 100 g of solvent at a given temperature • varies with temp • based on a saturated solution
UNSATURATED SOLUTION more solute dissolves SATURATED SOLUTION no more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form Solubility (Qualitative descriptions) concentration
Qualitative Description of Solution Concentration • SUPERsaturated - contains more dissolved solute than a saturated solution under the same conditions • Saturated - contains the maximum amount of solute that may be dissolved under existing conditions • UNsaturated - contains less solute than a saturated solution under existing conditions
Solubility Curve • shows the dependence of solubility on temperature
Quantitative Description of Solution Concentration The concentration of a solution measured in moles of solute per liter of solution. Molarity, M = moles U L of sol’n
Preparation of Molar Solutions Problem: How many grams of sodium chloride are needed to prepare 1.50 liters of 0.500 M NaCl solution? • Step #1: Ask “How Much?” (What volume to prepare?) • Step #2: Ask “How Strong?” (What molarity?) • Step #3: Ask “What does it weigh?” (Molar mass is?) 1.50 L 0.500 mol 58.44 g = 43.8 g 1 L 1 mol Place 43.8g NaCl(s) into a volumetric flask. Add enough water to make 1.50L of the solution.
TRY: Calculate the molarity of 11.85g potassium permanganate dissolved in enough water to make a 750.mL solution. M = moles U = (11.85g * 1mole/158g) L of sol’n 0.750L = 0.100M
TRY: Calculate the mass of sodium chloride needed for 175mL of a 0.500M solution. M = moles U L of sol’n 0.500M = x 0.175L , where x = 0.0875 moles NaCl 0.0875 moles NaCl 58.5g NaCl = 5.12g NaCl 1 mole NaCl
Calculate the concentration of all ions 0.25M CaCl2 0.25M 0.50M 0.25M CaCl2(s) Ca2+(aq) + 2Cl-(aq) 2M CrCl3 2M 6M 2M CrCl3(s) Cr3+(aq) + 3Cl-(aq)
TRY: What is the [Cl-] in solution made from 9.82g copper (II) chloride to make 600.mL of solution. 1st calculate [solute] M = moles U/L sol’n = (9.82g CuCl2 * 1mole/134.5g CuCl2) 0.600L = 0.122M Then write the dissociation equation CuCl2(s) Cu+2(aq) + 2Cl-(aq) Calculate [Cl-] 0.122M CuCl22 moles Cl- = 1 mole CuCl2 = 0.244M Cl-
TRY:(a) What is the [SO4-2] when 48.05g iron (III) sulfate is mixed with enough water to make 800.mL of solution. (b) Find [Fe+3]. Fe2(SO4)3(s) 2Fe+3(aq) + 3SO4-2(aq) [ Fe2(SO4)3 ] = (48.05g Fe2(SO4)3* 1mole/400g Fe2(SO4)3) 0.800L = 0.150 M (a) [ SO4-2] = 0.150M Fe2(SO4)3 3 moles SO4-2 1 mole Fe2(SO4)3 = 0.450M SO4-2 (b) [ Fe+3] = 0.150M Fe2(SO4)3 2 moles Fe+3 1 mole Fe2(SO4)3 = 0.300M Fe+3
Serial Dilution It is not practical to keep solutions of many different concentrations on hand, so chemists prepare more dilute solutions from a more concentrated “stock” solution.
Dilution Adding water to get desired M M1V1 = M2V2 MstockVstock = MdiluteVdilute (moles/L)*(L) = (moles/L)*(L) moles = moles !!!!!! Calculate the volume of 11.6M HCl needed for 250mL of 3.0M HCl. (11.6 M)(Vstock ) = (3.0 M)(0.250 Liters) Vstock = (3.0 M)(0.250 Liters) 11.6 M Vstock = 0.065 L
Dilution Adding water to get desired M M1V1 = M2V2 How much 9.00M NaOH is needed to make 1200.mL of a 1.00M NaOH solution? (9.00 M)(Vstock ) = (1.00 M)(1200. mL) Vstock = (1.00 M)(1200. mL) 9.00 M Vstock = 133 mL
4.4 Types of Reactions Ppt (precipitation) Rxns Redox Rxns Acid-Base Rxns
5 Reactions from 1st Year Chem Synthesis (Combination) Reaction A + B AB Decomposition (Analysis) Reaction AB A + B Single Replacement Reaction M + BX MX + B N + BX BN + X Double Replacement Reaction AX + BY AY + BX Combustion Reaction Hydrocarbon + O2 CO2 + H2O
Synthesis (Combination) Reactions Two or more reactants combine to form a single product A + B AB 2Na + Cl2 2NaCl NOTE: “reactants”, not necessarily “elements”
Synthesis (Combination) Reactions Two or more reactants combine to forma single product Common synthesis reactions include: Metallic Oxide + Water Base (Hydroxide) MgO + HOH Mg(OH)2 Nonmetallic Oxide + Water Acid CO2 + H2O H2CO3 Metallic + Nonmetallic Ionic Compound Oxide Oxide (Salt) MgO + CO2 MgCO3
Decomposition (Analysis) Reactions Single reactant broken down into two or more products AB A +B Common decomposition reactions include: Metallic Metallic + CO2 Carbonate Oxide MgCO3 MgO + CO2 Metallic Metallic + O2 Chlorate Chloride Mg(ClO3)2MgCl2 + 3O2
Decomposition (Analysis) Reactions Single reactant broken down into two or more products AB A +B Common decomposition reactions include: (NH4)2CO3 2NH3 + H2CO3 CO2 + H2O NH4OH NH3 + H2O H2SO3 H2O + SO2 2H2O2 2H2O + O2
Single Replacement Reactions M + BX MX + B If element M is a metal, it may replace cation B. N + BX BN + X If element N is a nonmetal, it may replace anion X. Why “may”? Cooper, you’re getting wishy-washy on me. It depends on which is more reactive: M or B, N or X.
The Activity Series of the Metals Metals can replace other metals provided that they are above the one they are trying to replace. Metals from sodium upward can replace hydrogen in water • Lithium • Potassium • Calcium • Sodium • Magnesium • Aluminum • Zinc • Chromium • Iron • Nickel • Lead • Hydrogen • Bismuth • Copper • Mercury • Silver • Platinum • Gold Significance Metals above hydrogen can replace it in acids.
The Activity Series of the Halogens • Fluorine • Chlorine • Bromine • Iodine Halogens can replace other halogens in compounds, provided that they are above the one they’re trying to replace. 2NaCl(s) + F2(g) 2NaF(s) + Cl2(g) ??? MgCl2(s) + Br2(l) No Reaction ???
Double Replacement Reactions The ions of two compounds exchange places in an aqueous solution to form two new compounds. AX + BY AY + BX • One of the compounds formed is usually • a precipitate (an insoluble solid), • a gas that bubbles out of solution, or • water.
4.5 Precipitation Reactions Solubility Rules – Mostly Soluble