Stoichiometry …like a beautiful sunset on a serene lake – NOT!

1. Stoichiometry…like a beautiful sunset on a serene lake – NOT!

2. What the heck is Stoichiometry • Stoichiometry is the study of quantities of materials produced and consumed in chemical reactions. Or, in a way normal people (not honors students) could understand… …solving problems using relationships found in balanced, chemical equations!

3. MOLE (a mole is a unit or have you heard containing 6 x 10 to the 23rd) • A mole is a counting number used by chemists …Kind of like 1 dozen eggs – 12 eggs Avogadro defined the mole as the number of Carbon atoms in exactly 12 grams of pure Carbon – 12 (think the graphite in a pencil!) It was determined that 1 mole = 6.02 x 1023 units The units are usually atoms or molecules This number is called AVOGADRO’S NUMBER!

4. Just How Big is This Number? (not as big as your hips or mouth!!) • How big is 6.02 x 1023 ? A huge number! • 1 mole of marbles would cover the entire earth a depth of 50 miles! • 1 mole sheets of paper would go to the moon and back 80 billion times. • 1 mole of pennies- each of us on earth could spend 1 million dollars each hour (day and night) and have ½ of it left if we died at age 70! (Much too big a number to comprehend)

5. Comparisons of 1 mole of different elements

6. So… what is the connection between moles and atomic weights? • The atomic weights (or the mass numbers or the atomic masses) of the elements on the periodic table are equal to 1 mole of that substance. That’s why we LOVE the periodic table!

7. You have 10 g of Al. Calculate the number of moles AND the number of atoms . • Remember: the mass of 1 mole of Al equals 26.98 or 27 grams (the at. wt.)

8. Mole Map

9. A silicon chip used in your cell phone has a mass of 5.68 mg (which is 0.00568g). How many Si atoms are present in this chip?

10. Co is a metal added to steel (a mixture) to help the steel resist corrosion. You have 5.00 x 1020 atoms of Co. Calculate: • The number of moles: • The mass of Cobalt:

11. Molecular or Formula Weights • A formula weight gives the mass of 1 mole of a molecule. • Find the formula weight of CH4(a byproduct of Chipotle)

12. Calculate the formula weight of NaCl

13. Calculate the formula weight of C10 H6 O3 , a natural herbicide (weed killer) and dye in Rit Dye.

14. Now, nerds of the world…calculate the number of moles of C10 H6 O3 in 0.0156 g

15. Isopentyl acetate (C7H14O2) is the compound responsible for the scent of bananas. Bee’s also release this same compound when they sting in order to attract other bees (to the buffet) and join in the attack. (smell you bee sting next time!) They release 1 microgram in each bee sting. • How many molecules of C7H14O2 are released in one bee sting?

16. How many atoms of C are present in one bee sting? (a fact you have always wanted to know)

17. Percent Composition • Ethanol, an additive to gas (and alcoholic drinks) has the formula C2H5OH. Find the % of each element in ethanol. STEP 1: STEP 2:

18. Find the mass % of each element in C10H14 O

19. Penicillin, an antibiotic, has the formula C14H20N2SO4. • Find the % of Nitrogen in penicillin. • Find the number of moles of penicillin if you give a patient a 250 mg tablet.

20. Empirical Formulas • A empirical formula is the simplest, whole number ratio of atoms. Most formulas are empirical. What is the key? If it CAN’T be reduced, it is empirical. If it CAN be reduced, it is a molecular formula. What are these? Na2SO4 C12H22O11 C6H12O6 N4O12

21. To find the Empirical Formula (from %) • Convert % data to grams (% means “parts per hundred”). • Convert the grams to moles (÷ by the atomic weight) • Divide by the smallest to the get the simplest, whole-number ratio.

22. The junior scientist was given 38.67% C, 16.23% H and 45.1% N. Find the empirical formula.

23. A white powder was found near where mole died and was found to contain 43.64% P and 56.36% O. Find the empirical formula and name this molecule.

24. How many grams of potassium can be produced when 150.6 g of potassium sulfate is completely decomposed? First, find the % of K in K2SO4 Next, multiply the % (decimal) by the mass given.

25. How many grams of Cu are needed to make 16.6 g of copper II phosphate? First, find the % of Cu: Second, multiply the % by the mass given:

26. Molecular Formulas • A molecular formula is NOT the simplest formula (it can be reduced…but don’t do it!) • Formula: • W • Where X is an integer

27. A compound with an empirical formula of CH5N has a molecular weight of 93 g/mole. Find the molecular formula.

28. Find the empirical and molecular formulas (normal kids don’t get to do this….you’re lucky!) for a compound that is 71.65% Cl, 24.27% C, and 4.07% H. The molecular formula weight is 98.96 g/mol. Four Steps to find the Molecular Formula: • Find the empirical formula: • Find the empirical formula weight:

29. 3. Find X (X = Molec.fwt/Emp. Fwt) 4. Multiply X by the empirical formula to get the molecular formula.

30. Chemical Equations • CH4 + O2 → CO2 + H2O • In a chemical reaction, atoms have been rearranged but have NOT been created or destroyed. This is why we have to balance every chemical reaction/equation. • Balance CH4 + O2 → CO2 + H2O • Balance HCl + NaHCO3 → CO2 + H2O + NaCl • When balancing equations, the formulas must NEVER be changed. We may just add coefficients.

31. Balance the following reactions: • C2H5OH + O2 → CO2 + H2O • (NH4 )2Cr2O7 → Cr2 O3 + N2 + H2O • C3H8 + O2 → CO2 + H2O • NH3 + O2 → NO + H2O

32. Diatomic Elements • N2 , Cl2 , O2 , H2 , I2 , Br2 , F2 • Memory aid: I Bring Clay For Our New House • Or Never Collect Our House Insurance Before Friday (this one is ghetto!) • Diatomic elements always combine with a like atom when they are a free element. • An arrow pointing up (↑) indicates a gas. The abbreviation ppt. or a down arrow (↓) indicates a precipitate.

33. Chemical equations indicate a… • Chemical change. Remember, they must obey the Law of Conservation of Mass – the number of atoms of the reactants MUST equal the number of atoms of products. • The coefficients from the balanced equation tell us the mole ratios of reacting substances (this will be important later!!!) • 2K + S → K2S • 2FeCl3 + 3Ca(OH)2 → 2Fe(OH)3 + 3CaCl2

34. Five Types of Chemical Reactions • 1. Composition (or Combination) Reactions • A + B → AB • Sodium and sulfur yields _____________ 1. complete the word equation 2. write the correct formulas 3. Balance that bad boy!

35. Aluminum and iodine yields ??

36. 2. Decomposition Reactions (6 types) • Generic equation AB → A + B • These are the opposite of Composition Reactions. • Here, one thing is HEATED and it breaks down into two things. • The best way to learn these six types of equations is to MEMORIZE them!!!

37. 1. Binary Compound into Elements • Arsenic III oxide yields when heated ______________ + ________________ • Water yields with electricity _____________ + ____________.

38. 2. Metal Carbonates form metal oxides and carbon dioxide • Magnesium carbonate yield when heated _________________+ _________________ • Sodium carbonate yields when heated _________________ + _________________

39. 3. Metal hydroxides yield metal oxides and water • Potassium hydroxide yields when heated __________________ +________________ • Calcium hydroxide yields when heated _________________ + _________________

40. 4. Metal chlorates yield metal chlorides and oxygen • Potassium chlorate yields when heated _________________ + ___________________

41. 5. Metallic bromates yields metal bromides and oxygen • Calcium bromate yields when heated _________________ + _________________ • Iron II bromate yields when heated _________________ + _________________

42. 6. Acids when heated form nonmetal oxides and water • Carbonic acid when heated yields _________________ + __________________

43. 3. Single Replacement Reactions (two types) • A. Positive Replacement (3 types) • AX + B → BX + A • The single element will replace the positive element in the compound

44. 1. Replacement of a Metal by a more active metal • Magnesium and calcium nitrate yields

45. 2. Replacement of hydrogen in water by a metal (to form a metallic hydroxide and hydrogen gas) • Aluminum and water yields

46. 3. Replacement of H in an acid by a metal • Aluminum and hydrochloric acid yields

47. B. Negative Replacement - Replacement of Halogens (1 type) • A + MB → MA + B • The halogens are Br-1 , Cl-1 , F -1 , and I-1 and they are all diatomic when they stand alone (Br2 , Cl2 , F2 , and I2 )

48. Hydrochloric acid and bromine yields…

49. 4. Ionic/Exchange/Double Replacement Reactions • AB + CD → AD + CB • The product MAY produce a solid or a precipitate • PRECIPITATE: an insoluble substance formed in solution. •a liquid + liquid → solid • but only one of the products may be a precipitate

50. Solubility Rules • See chart in your book, the chart in your handouts section or on the back of your Chem Helper.