Chapter 4

1. Chapter 4 Chemical Quantities and Aqueous Reactions

2. What Happens When a Solute Dissolves? • there are attractive forces between the solute particles holding them together • there are also attractive forces between the solvent molecules • when we mix the solute with the solvent, there are attractive forces between the solute particles and the solvent molecules • if the attractions between solute and solvent are strong enough, the solute will dissolve

3. Table Salt Dissolving in Water Each ion is attracted to the surrounding water molecules and pulled off and away from the crystal When it enters the solution, the ion is surrounded by water molecules, insulating it from other ions The result is a solution with free moving charged particles able to conduct electricity Tro, Chemistry: A Molecular Approach

4. Electrolytes and Nonelectrolytes • materials that dissolve in water to form a solution that will conduct electricity are called electrolytes • materials that dissolve in water to form a solution that will not conduct electricity are called nonelectrolytes Tro, Chemistry: A Molecular Approach

5. Molecular View of Electrolytes and Nonelectrolytes • in order to conduct electricity, a material must have charged particles that are able to flow • electrolyte solutions all contain ions dissolved in the water • ionic compounds are electrolytes because they all dissociate into their ions when they dissolve • nonelectrolyte solutions contain whole molecules dissolved in the water • generally, molecular compounds do not ionize when they dissolve in water • the notable exception being molecular acids Tro, Chemistry: A Molecular Approach

6. ionic compounds dissociate into ions when they dissolve molecular compounds do not dissociate when they dissolve Salt vs. Sugar Dissolved in Water Tro, Chemistry: A Molecular Approach

7. Acids • acids are molecular compounds thationizewhen they dissolve in water • the molecules are pulled apart by their attraction for the water • when acids ionize, they form H+cations and anions • the percentage of molecules that ionize varies from one acid to another • acids that ionize virtually 100% are called strong acids HCl(aq)  H+(aq) + Cl-(aq) • acids that only ionize a small percentage are called weak acids HF(aq)  H+(aq) + F-(aq) Tro, Chemistry: A Molecular Approach

8. Strong and Weak Electrolytes • strong electrolytesare materials that dissolve completely as ions • ionic compounds and strong acids • their solutions conduct electricity well • weak electrolytesare materials that dissolve mostly as molecules, but partially as ions • weak acids • their solutions conduct electricity, but not well • when compounds containing a polyatomic ion dissolve, the polyatomic ion stays together Na2SO4(aq) 2 Na+(aq) + SO42-(aq) HC2H3O2(aq)  H+(aq) + C2H3O2-(aq) Tro, Chemistry: A Molecular Approach

9. Classes of Dissolved Materials Tro, Chemistry: A Molecular Approach

10. Solubility of Ionic Compounds • compounds that dissolve in a solvent are said to be soluble, while those that do not are said to beinsoluble • NaCl is soluble in water, AgCl is insoluble in water • the degree of solubility depends on the temperature • even insoluble compounds dissolve, just not enough to be meaningful Tro, Chemistry: A Molecular Approach

11. When Will a Salt Dissolve? • Predicting whether a compound will dissolve in water is not easy • The best way to do it is to do some experiments to test whether a compound will dissolve in water, then develop some rules based on those experimental results • we call this method the empirical method Tro, Chemistry: A Molecular Approach

12. Solubility Rules

13. Precipitation Reactions • reactions between aqueous solutions of ionic compounds that produce an ionic compound that is insoluble in water are called precipitation reactionsand the insoluble product is called a precipitate Tro, Chemistry: A Molecular Approach

14. 2 KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2 KNO3(aq)

15. No Precipitate Formation = No Reaction KI(aq) + NaCl(aq)  KCl(aq) + NaI(aq) all ions still present,  no reaction Tro, Chemistry: A Molecular Approach

16. Example 4.10 – Write the equation for the precipitation reaction between an aqueous solution of potassium carbonate and an aqueous solution of nickel(II) chloride • Write the formulas of the reactants K2CO3(aq) + NiCl2(aq)  • Determine the possible products • Determine the ions present (K+ + CO32-) + (Ni2+ + Cl-)  • Exchange the Ions (K+ + CO32-) + (Ni2+ + Cl-)  (K+ + Cl-) + (Ni2+ + CO32-) • Write the formulas of the products • cross charges and reduce K2CO3(aq) + NiCl2(aq)  KCl + NiCO3

17. Example 4.10 – Write the equation for the precipitation reaction between an aqueous solution of potassium carbonate and an aqueous solution of nickel(II) chloride • Determine the solubility of each product KCl is soluble NiCO3 is insoluble • If both products soluble, write no reaction does not apply since NiCO3 is insoluble Tro, Chemistry: A Molecular Approach

18. Example 4.10 – Write the equation for the precipitation reaction between an aqueous solution of potassium carbonate and an aqueous solution of nickel(II) chloride • Write (aq) next to soluble products and (s) next to insoluble products K2CO3(aq) + NiCl2(aq)  KCl(aq) + NiCO3(s) • Balance the Equation K2CO3(aq) + NiCl2(aq)  2 KCl(aq) + NiCO3(s) Tro, Chemistry: A Molecular Approach

19. Ionic Equations • equations which describe the chemicals put into the water and the product molecules are called molecular equations 2 KOH(aq) + Mg(NO3)2(aq) ® 2 KNO3(aq) + Mg(OH)2(s) • equations which describe the actual dissolved species are called completeionic equations • aqueous strong electrolytes are written as ions • soluble salts, strong acids, strong bases • insoluble substances, weak electrolytes, and nonelectrolytes written in molecule form • solids, liquids, and gases are not dissolved, therefore molecule form 2K+1(aq) + 2OH-1(aq) + Mg+2(aq) + 2NO3-1(aq)® 2K+1(aq) + 2NO3-1(aq) + Mg(OH)2(s) Tro, Chemistry: A Molecular Approach

20. Ionic Equations • ions that are both reactants and products are called spectator ions 2K+1(aq) + 2OH-1(aq) + Mg+2(aq) + 2NO3-1(aq)® 2K+1(aq) + 2NO3-1(aq) + Mg(OH)2(s) • an ionic equation in which the spectator ions are • removed is called a net ionic equation • 2OH-1(aq) + Mg+2(aq)® Mg(OH)2(s) Tro, Chemistry: A Molecular Approach

21. Example • Write a balanced molecular equation, ionic equation and net ionic equation for the following reactions: • K2S(aq) + Fe(NO3)2(aq)  • NaCl(aq) + NH4(aq)CO3 

22. Acid-Base Reactions • also called neutralization reactionsbecause the acid and base neutralize each other’s properties 2 HNO3(aq) + Ca(OH)2(aq)  Ca(NO3)2(aq) + 2 H2O(l) • the net ionic equation for an acid-base reaction is H+(aq) + OH(aq)  H2O(l) • as long as the salt that forms is soluble in water Tro, Chemistry: A Molecular Approach

23. Acids and Bases in Solution • acids ionize in water to form H+ ions • more precisely, the H from the acid molecule is donated to a water molecule to form hydronium ion, H3O+ • most chemists use H+ and H3O+ interchangeably • bases dissociate in water to form OH ions • bases, like NH3, that do not contain OH ions, produce OH by pulling H off water molecules • in the reaction of an acid with a base, the H+ from the acid combines with the OH from the base to make water • the cation from the base combines with the anion from the acid to make the salt acid + base salt + water Tro, Chemistry: A Molecular Approach

24. Common Acids

25. Common Bases Tro, Chemistry: A Molecular Approach

26. HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) Tro, Chemistry: A Molecular Approach

27. Example • Write the molecular, ionic, and net-ionic equation for the reaction of • aqueous nitric acid with aqueous calcium hydroxide • Aqueous sulfuric acid and aqueous potassium hydroxide • Aqueous hydrofluoric acid and aqueous sodium hydroxide Tro, Chemistry: A Molecular Approach