JCHS Honors Chemistry Spring Final S.G

1. JCHS Honors Chemistry Spring Final S.G CH Williams

2. Question • Which of the following substances act as catalysts in the body? • Carbohydrates • Lipids • Teeth • enzymes • Nucleic acids

3. Questions • In an endothermic reaction at equilibrium, what is the effect of raising the temperature? • The reaction makes more products

4. Question • Activation energy is • An energy barrier between reactants and products

5. Question • A + BC -- B + AC is an example of a • Single replacement reaction

6. Review: Chemical Equations C2H5OH + 3O2® 2CO2 + 3H2O reactants products When the equation is balanced it has quantitative significance: Chemical change involves a reorganization of the atoms in one or more substances. 1 mole of ethanol reacts with 3 moles of oxygen to produce 2 moles of carbon dioxide and3 moles of water

7. Calculating Masses of Reactants and Products • Balance the equation. • Convert mass or volume to moles, if necessary. • Set up mole ratios. • Use mole ratios to calculate moles of desired substituent. • Convert moles to mass or volume, if necessary.

8. Working a Stoichiometry Problem 6.50 grams of aluminum reacts with an excess of oxygen. How many grams of aluminum oxide are formed. 1. Identify reactants and products and write the balanced equation. 4 Al + 3 O2 2 Al2O3 a. Every reaction needs a yield sign! b. What are the reactants? c. What are the products? d. What are the balanced coefficients?

9. Working a Stoichiometry Problem 6.50 grams of aluminum reacts with an excess of oxygen. How many grams of aluminum oxide are formed? 4 Al + 3O2 2Al2O3 6.50 x 2 x 101.96÷ 26.98 ÷ 4 = 12.3 g Al2O3 6.50 g Al 1 mol Al 2 mol Al2O3 101.96 g Al2O3 = ? g Al2O3 4 mol Al 1 mol Al2O3 26.98 g Al

10. Limiting Reactant The limiting reactant is the reactant that is consumed first, limiting the amounts of products formed.

11. Calculations of Solution Concentration:Molarity Molarity is the ratio of moles of solute to liters of solution

12. 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?) 1.500 L 0.500 mol 58.44 g = 43.8 g 1 L 1 mol

13. Serial Dilution Problem: What volume of stock (11.6 M) hydrochloric acid is needed to prepare 250. mL of 3.0 M HCl solution? MstockVstock = MdiluteVdilute (11.6 M)(x Liters) = (3.0 M)(0.250 Liters) x Liters = (3.0 M)(0.250 Liters) 11.6 M = 0.065 L

14. Solutions

15. Solute A solute is the dissolved substance in a solution. Saltin salt water Sugarin soda drinks Carbon dioxide in soda drinks Solvent A solvent is the dissolving medium in a solution. Waterin salt water Waterin soda

16. “Like Dissolves Like” Nonpolar solutesdissolve best in nonpolar solvents Polar and ionic solutesdissolve best in polar solvents

17. Solubility Trends • The solubility of MOST solids increases with temperature. • The rate at which solids dissolve increases with increasing surface area of the solid. • The solubility of gases decreases with increases in temperature. • The solubility of gases increases with the pressure above the solution.

18. Therefore… Solids tend to dissolve best when: • Heated • Stirred • Ground into small particles Gases tend to dissolve best when: • The solution is cold • Pressure is high

19. Saturation of Solutions • A solution that contains the maximum amount of solute that may be dissolved under existing conditions is saturated. • A solution that contains less solute than a saturated solution under existing conditions is unsaturated. • A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated.

20. 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.

21. 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.

22. Try to classify the following substances as electrolytes or nonelectrolytes… • Pure water • Tap water • Sugar solution • Sodium chloride solution • Hydrochloric acid solution • Lactic acid solution • Ethyl alcohol solution • Pure sodium chloride

23. Answers to Electrolytes NONELECTROLYTES: ELECTROLYTES: • Pure water • Sugar solution • Ethanol solution • Pure NaCl • Tap water (weak) • NaCl solution • HCl solution • Lactate solution (weak)

24. Ionic Compounds “Dissociate” 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)

25. 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).

26. Precipitation Reactions Graphic: Wikimedia Commons User Tubifex

27. 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), an insoluble gas that bubbles out of solution, or a molecular compound, usually water.

28. Double replacement forming a precipitate… Lead(II) nitrate + potassium iodide  lead(II) iodide + potassium nitrate Double replacement (ionic) equation Pb(NO3)2(aq) + 2KI(aq)  PbI2(s) + 2KNO3(aq) Complete ionic equation shows compounds as aqueous ions Pb2+(aq) + 2 NO3-(aq) + 2 K+(aq) +2 I-(aq)  PbI2(s) + 2K+(aq) + 2 NO3-(aq) Net ionic equation eliminates the spectator ions Pb2+(aq) + 2 I-(aq)  PbI2(s)

29. Solubility Chart:Common saltsat 25C S = Soluble I = Insoluble P = Partially Soluble X = Other

30. ACIDS AND BASES www.lab-initio.com

31. Properties of Acids • Acids are proton (hydrogen ion, H+) donors • Acids have a pH lower than 7 • Acids taste sour • Acids effect indicators • Blue litmus turns red • Methyl orange turns red • Acids react with active metals, producing H2 • Acids react with carbonates • Acids neutralize bases

32. Acids are Proton (H+ ion) Donors Strong acids are assumed to be 100% ionized in solution (good H+donors). HCl H2SO4 HNO3 Weak acids are usually less than 5% ionized in solution (poor H+donors). H3PO4 HC2H3O2 Organic acids

33. Acids Have a pH less than 7

34. Acids React with Active Metals Acids react with active metals to form salts and hydrogen gas. Mg + 2HCl  MgCl2 + H2(g) Zn + 2HCl  ZnCl2 + H2(g) Mg + H2SO4 MgSO4 + H2(g)

35. AcidsReact withCarbonates 2HC2H3O2+Na2CO3 2 NaC2H3O2 + H2O + CO2

36. Acids Neutralize Bases Neutralization reactions ALWAYSproduce a saltandwater. HCl + NaOH NaCl+H2O H2SO4 + 2NaOH  Na2SO4+2H2O 2HNO3 + Mg(OH)2 Mg(NO3)2+2H2O

37. Properties of Bases • Bases are proton (hydrogen ion, H+) acceptors • Bases have a pH greater than 7 • Bases taste bitter • Bases effect indicators • Red litmus turns blue • Phenolphthalein turns purple • Solutions of bases feel slippery • Bases neutralize acids

38. Bases are Proton (H+ ion) Acceptors • Sodium hydroxide (lye), NaOH • Potassium hydroxide, KOH • Magnesium hydroxide, Mg(OH)2 • Calcium hydroxide (lime), Ca(OH)2 OH-(hydroxide) in base combines with H+in acids to form water H+ + OH- H2O

39. Bases Effect Indicators Red litmus paper turns blue in contact with a base. Phenolphthalein turns bright pinkin a base.

40. Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH)2 MgCl2 + 2 H2O

41. Gases

42. The Nature of Gases • Gases expand to fill their containers • Gases are fluid – they flow • Gases have low density • 1/1000 the density of the equivalent liquid or solid • Gases are compressible • Gases effuse and diffuse

43. Ideal Gases Ideal gases are imaginary gases that perfectly fit all of the assumptions of the kinetic molecular theory. • Gases consist of tiny particles that are • far apart relative to their size. • Collisions between gas particles and between • particles and the walls of the container are • elastic collisions • No kinetic energy is lost in elastic • collisions

44. Ideal Gases (continued) • Gas particles are in constant, rapid motion. • They therefore possess kinetic energy, the • energy of motion • There are no forces of attraction • between gas particles • The average kinetic energy of gas • particles depends on temperature, not • on the identity of the particle.

45. Pressure Pressure is the force created by the collisions of molecules with the walls of a container

46. Standard Pressure • 1 standard atmosphere (atm) • 101.3 kPa (kilopascals) • 14.7 lbs/in2 • 760 mm Hg (millimeters of mercury) • 760 torr

47. Measuring Pressure The first device for measuring atmospheric pressure was developed by Evangelista Torricelli during the 17th century. The device was called a “barometer” • Baro = weight • Meter = measure

48. The Kelvin Scale

49. Standard Temperature and Pressure“STP” • Either of these: • 273 Kelvin (273 K) • 0 C • And any one of these: • 1 atm • 101.3 kPa • 14.7 lbs/in2 (psi) • 760 mm Hg • 760 torr

50. Gas Laws Robert Boyle Jacques Charles Amadeo Avogadro Joseph Louis Gay-Lussac