Reactions day one

1. Reactions day one Three types: Precipitation Acid & base Redox

2. Reactions in Solution (or precipitation reactions) • What we need to know • Dissolving • Molarity • Solubility rules • Use to predict if reaction occurs • Predicting products of reactions • Net ionic equations

3. Dissolving • How water dissolves substances • Check out this clip

4. Molarity • A measure of concentration of solute in a solution • Has units of moles solute/ L of solution • Equations • M = mole/V • Usually mass to solution or in stoich • M1 V1 = M2 V2 • This is for a dilution of an exiting solution

5. Molarity • A volume of 15 mL of 0.50 M NaCl is measured out for a lab. What is the mass of NaCl present in this sample? • 0.44g NaCl • What is the molarity of a solution that is prepared by diluting 8.3mL of 12 M HCl to a volume of 1000.0 mL? • 0.10M HCl

6. Solubility Rules • The ugly truth • The up side • Until the test have the guide handy but wean yourself from it before the test • Check p. 145 for different presentation of rules

7. Predicting precip. products • Usually ionic compounds • Like a dysfunctional couples dance • AX + BZ → AZ + BX • After determining products check states • If there is a solid or gas formed, the reaction occurs • If everything is still aqueous, there is no reaction and NR should be written in place of products

8. Predicting precip. products • Try these: • AgNO3 (aq)+ CuCl2 (aq) • K2CrO4 (aq) + Ba(CH3CO2)2 (aq) • NH4Cl (aq) + Na3PO4 (aq) • Answers: • AgCl(s) + Cu(NO3)2 (aq) • BaCrO4 (s) + KCH3CO2 (aq) • NR

9. Net Ionic equations • Shows only the substances that are involved in chemical changes • Spectator ions (ions that are unchanged in the reaction) are left out

10. Net Ionics • The long way: • KI (aq) + Pb(NO3)2 (aq)→ KNO3 (aq) + PbI2 (s) • Show all dissolved compounds as ions • K1+ + I1- + Pb2+ + NO31-→ K1+ +NO31- + PbI2 • Cross out what is not changed • K1+ + I1- + Pb2+ + NO31-→ K1+ +NO31- + PbI2 • Net ionic is the stuff left over, write it out • I1- + Pb2+ → PbI2 (s)

11. Net Ionics • The short way: • AgNO3(aq) + NaCl(aq)→ AgCl(s) + NaNO3(aq) • Take the non-aqueous as a product and then determine the reactants used to form them • Ag1+ + Cl1-→ AgCl(s)

12. HW • Ch. 4: #8 (a-c), 9 (a,b), 12 (a,b), 19-23, 26

13. Acid-Base reactions • What we need to know: • What are they? • How to write products • Ratios for neutralization

14. What are they? • Definitions vary in specificity but… • Acids typically contain H atoms that will break off (dissociate) in solution • Bases typically contain OH ions that will dissociate • Both can vary in strength depending on amount of H+ or OH- that forms in solution

15. What are they? • Common acids: • HCl, H2SO4, HBr, CH3COOH, see your poly sheet for more… yep you need to know them • Common bases: • NaOH, Ca(OH)2, Mg(OH)2, KOH, get the picture?

16. How to write products • Does this look familiar? • AX + BZ → AZ + BX • Try one • Mg(OH)2 (aq) + HI (aq)→ • MgI2(aq) + H2O(l) • One of the products will (almost) always be there in an acid base reaction, which one?

17. Neutralization • When moles of H+ = moles of OH- • Need a balanced equation • Basically it is stoich along with molarity… yea!

18. Neutralization • What amount of moles of HCl is needed to neutralize 5 moles of Mg(OH)2? • Mg(OH)2 (aq) + 2 HCl (aq)→ MgCl2(aq) + 2 H2O(l) • 5 moles Mg(OH)2 x (2 mol HCl / 1 mol Mg(OH)2) = 10 moles HCl • What if the problem were… What volume of 1.0M HCl is rq’d to neutralize 50.0 mL of 0.10M Mg(OH)2 (aq)? • Answer: 0.010 L or 10. mL of HCl

19. HW • Ch. 4 p. 176 #31, 32, 35, 36 • Introduction to Red-Ox reactions • Read 157 – 163 • Answer questions #41 (a-e), 42 (a-e) and 43 • Should be able to: • Assign oxidation states • Know definition of: • Oxidation, reduction, oxidizing agent, reducing agent