Chem 1035 Chapter 4 1 of 56Chapter 4Three Major Classes of Chemical ReactionsMany reactions take place in solution, which is a homogeneous mixture.Two parts of a solution:Solute:Solvent:We need a way to express the ratio of the components in the solution (since the composition is variable):Concentration unit:Molarity:
Chem 1035 Chapter 4 2 of 56Two ways to prepare a solution of a given molarity:1.Dissolving the solute in the solvent:Example Problem: How do you prepare 350. mL of a 0.250 Msolution of KNO3?
Chem 1035 Chapter 4 3 of 56
Chem 1035 Chapter 4 4 of 562. By dilution of an existing solution: Add water to an existing solution.
Example Problem: How do you prepare 500. mL of a 0.150 Msolution of KNO3, starting with the 0.250 Msolution prepared in the problem above?
Chem 1035 Chapter 4 5 of 56In this chapter, we will discuss reactions that take place in aqueous solution.Aqueoussolution: Water is the solvent.Water interacts strongly with its solutes and often plays an active role in aqueousreactions. First, we need to understand what happens when a soluble compound dissolves in water. The type of compound determines the process: •Ionic compounds•Covalent (molecular) compounds•Acids
Chem 1035 Chapter 4 6 of 56Ionic Compounds (metal + nonmetal)Solideg. K2SO4attraction between oppositely charged particles holds ions together++++++++++++------Aqueous SolutionIonized: K2SO4(s) 2K+(aq) + SO42–(aq)++++++++++-----Note: polyatomic ions do not dissociate (ionize); these act as a unit:
Chem 1035 Chapter 4 7 of 56SO42–, not S and O ions separately.
Chem 1035 Chapter 4 8 of 56
Example Problem: How many Al3+ ions are present in 50.0 mL of1.25 Maluminum sulfate? How many SO42–ions?
Chem 1035 Chapter 4 9 of 56Molecular Compound (nonmetals)Pure Substanceeg. CH3OH No ions, only moleculesCovalent bonds (shared electrons) hold atoms together in a moleculeAqueous SolutionAtoms held together in a molecule by covalent bondsCH3OH (l) CH3OH(aq)
Chem 1035 Chapter 4 10 of 56Acids (contain ionizable H)Pure Substanceeg. HCl, HF Not composed of ions, but H+ionizesCovalent bonds hold atoms together in the moleculeAqueous Solutioncompletely ionizedORpartially ionizedHCl(aq) → H+(aq) + Cl–(aq)HF(aq) H+(aq) + F–(aq)Some acids completely ionize and some acids only partially ionize in solution.Type of compoundas soluteAmount ofions inDoes the solutionconduct electricity?