CHEM 161: Chapter 4 Notes v0914 page 1 of 34 Chapter 4: Solution Chemistry: The Hydrosphere Problems: 4.1-4.86, 4.91-134, 4.139-4.141, 4.143-4.144 4.1 SOLUTIONS ON EARTH AND OTHER PLACES aqueous solution: a solution where water is the dissolving medium (the solvent) – For example, when table salt (NaCl) is dissolved in water, it results in an aqueous solution of sodium chloride, NaCl(aq), with Na+ and Cl ions dissolved in water. – Note: The physical state aqueous,(aq), indicates an element or compound dissolved in water while the physical state liquid,(l), means a pure substance in the liquid state. Example: If you had to drink one on the following, which would you choose? NaCl(l) NaCl(aq) Explain why. Thus, recognize that aqueous and liquid are not the same! Thus, a solution consists of a solute dissolved in a solvent. solute: component present in smaller amount solvent: component present in greater amount The formation of a solution – As a solute crystal is dropped into a solution, the water molecules begin to pull apart the ionic compound ion by ion  solvent molecules surround the solute particles, forming a solvent cage  The ions are now hydrated (surrounded by polar water molecules).  The solute is now dissolved in the solvent and cannot be seen because the ions are far apart, like the particles in a gasCHEM 161: Chapter 4 v0914 page 2 of 34 UNSATURATED, SATURATED, AND SUPERSATURATED SOLUTIONS If a solid is soluble in a solvent, more solid dissolves in the solvent at higher temperatures. unsaturated: contains less than the maximum amount of solute that a solvent can hold at a specific temperature saturated: contains the maximum amount of solute that a solvent can hold at a specific temperature supersaturated: contains more than the maximum amount of solute that a solvent should be able to hold at specific temperature A supersaturated NaC2H3O2 solution recrystallizing after addition of more solute: How can a solution hold more solute than it should be able to hold? – If a given amount of solute is dissolved in a solvent at a higher temperature, and the solution is allowed to cool without being disturbed, the solute will remain in solution. But the solution is unstable, and the solute will come out of solution (i.e. recrystallize) if the solution is disturbed (e.g. by adding more solute, scratching the glass, etc.) For some substances, recrystallization is exothermic, releasing heat to the surroundings.  Hot packs used to warm hands and feet in winter For other substances, recrystallization is endothermic, absorbing heat and making the surroundings colder.  Cold packs used for sports injuriesCHEM 161: Chapter 4 Notes v0914 page 3 of 34 EVIDENCE OF A CHEMICAL REACTION a) A gas is produced. b) A precipitate forms. c) Heat is released/absorbed Types of Chemical Reactions - Precipitation Reactions - Acid-Base Neutralization Reaction - Oxidation-Reduction (Redox) Reactions – Also classified as combination, decomposition, combustion, and single-replacement reactions 4.7 PRECIPITATION REACTIONS Solubility Rules: Indicate if an ionic compound is soluble or insoluble in water. – Keep in mind that these are just general guidelines, and in reality, some ionic compounds may only be slightly soluble, and solubility may depend on temperature. Solubility Rules for Ionic Compounds in Water Soluble if the ionic compound contains: 1. Li+, Na+, K+, NH4+ (ALWAYS!) 2. C2H3O2–, NO3–, ClO3–, ClO4– 3. Halide ions (X–): Cl–, Br–, or I–, but AgX, PbX2, HgX, and Hg2X2 are insoluble 4. sulfate ion (SO42-), but CaSO4, SrSO4, BaSO4, Ag2SO4, `and PbSO4 are insoluble. Insoluble if the ionic compound contains: 5. carbonate ion, CO32- 6. chromate ion, CrO42- 7. phosphate ion, PO43- 8. sulfide ion (S2–), but CaS, SrS, and BaS are all soluble. 9. hydroxide ion (OH–), but Ca(OH)2, Sr(OH)2, and Ba(OH)2 are soluble. soluble = compound dissolves in water  exists as individual ions in solution  physical state is aqueous, (aq) insoluble = compound does not dissolve in water but remains a solid  physical state is shown as solid, (s)CHEM 161: Chapter 4 v0914 page 4 of 34 Ex. 1 Use the Solubility Rules and identify the ionic compounds are soluble or insoluble by indicating the physical state of each compound. a. NaCl d. LiOH g. Mg(OH)2 j. Ag3PO4 b. MgS e. CaS h. SrSO4 k. BaCO3 c. K3PO4 f. Li2CrO4 i. Na2CO3 l. (NH4)2CrO4 Ex. 2 Use your answers from Ex. 1 to draw each soluble compound as individual ions and each insoluble compound as a solid at the bottom of the beaker: NaCl MgS K3PO4 Ag3PO4 (NH4)2CrO4 In a precipitation reaction, two solutions react to form a precipitate (an insoluble solid): AX(aq) + BZ(aq)  AZ(s) + BX(aq) precipitate To balance and complete the following reactions: 1. Exchange the anions, writing the formulas for the products based on the charges of the ions! 2. Use the Solubility Rules to determine if each product is soluble or insoluble. – If at least one product is insoluble, a precipitate reaction has occurred, so write the formulas for both products, indicating the precipitate as(s), then balance the equation. – If both products are soluble—both(aq)—then write NR=no reaction. 3. Keep in mind that the charges on ions do NOT change in precipitation reactions.CHEM 161: Chapter 4 Notes v0914 page 5 of 34 For metals that can form more than one charge, use the charge on the metal ion from the reactant side of the equation. Ex 1. MgSO4(aq) + NaOH(aq)  +  Ex 2. K2CO3(aq) + AlCl3(aq)  +  Ex 3. SrBr2(aq) + Zn(NO3)2(aq)  + CHEM 161: Chapter 4 v0914 page 6 of 34 4.5 ACID-BASE (NEUTRALIZATION) REACTIONS: PROTON TRANSFER Properties of Acids and Bases Acids Bases – produce hydrogen ions, H+ – produce hydroxide ions, OH– – taste sour – taste bitter; feel soapy, slippery – turn blue litmus paper red – turn red litmus paper blue Arrhenius Definitions: acid: A substance that releases H+ when dissolved in water – Some acids are monoprotic