STOICHIOMETRY

STOICHIOMETRY PERCENTAGE COMPOSITION Part x 100 = % Whole Part = % 1. A sample of magnesium weighing 2.246 g burns in oxygen to form 3.724 g of magnesium oxide. What are the percentages of magnesium and oxygen in magnesium oxide? Part x 100 = % Whole Part = % Whole 100

2. Give the mass percentages of the elements in glucose, C6H12O6.

3. Determine the mass of carbon present in a sample of glucose weighing 5.4 g.

4. The mass percentages of aluminum and chlorine in aluminum chloride are: 20.24% aluminum and 79.76% chlorine. Determine the masses of the two elements in a sample weighing 25.60 g.

5. When 6. 20 g of nitrous oxide decomposes, 3 5. When 6.20 g of nitrous oxide decomposes, 3.95 g of nitrogen is produced. What are the mass percentages of nitrogen and oxygen in the compound?

THE MOLE RATIO = THE ATOM RATIO ! DETERMINING FORMULAS EMPIRICAL FORMULAS H2O1 : 2 atoms H : 1 atom O x 6.022 x 1023 x 6.022 x 1023 2 moles H : 1 mole O THE MOLE RATIO = THE ATOM RATIO !

DETERMINING FORMULAS 1. A certain compound contains 75.0% carbon and 25.0 % hydrogen. What is its simplest (empirical) formula?

2. Analysis: I: 76.0%, O: 24.0%. Find the empirical formula.

3. Acetic acid contains the elements carbon, hydrogen, and oxygen 3. Acetic acid contains the elements carbon, hydrogen, and oxygen. The mass percentages of these elements are 40.0%, 6.73%, and 53.3%, respectively. Determine the simplest formula of acetic acid.

MOLECULAR FORMULAS Molecular Empirical C6H12O6 C1H2O1 Mass: Mass: The mass of the molecular formula is 6 x the mass of the empirical formula! Just as the molecular formula is some WHOLE NUMBER multiple of the empirical formula. C1H2O1 180.18 30.03

4. A certain hydrocarbon is found to have the empirical formula CH3 4. A certain hydrocarbon is found to have the empirical formula CH3. Its molecular mass is 30. What is the molecular formula?

5. A compound is found by analysis to consist of 17.9% nitrogen and 82.1% sulfur. Its molecular mass is 156. Find its empirical formula and its molecular formula.

6. If the empirical formula of a compound is CH2 and its molecular mass is 42, find its molecular formula.

7. Given: Carbon: 92.3%, Hydrogen: 7.7% If the molecular mass of the compound is 78, find its molecular formula.

8. A compound containing nitrogen and oxygen is 30.4% nitrogen by mass. If the molar mass of the compound is 92.0 g/mole, find the compound’s empirical and molecular formulas.

CHEMICAL EQUATIONS

Chemical Reactions

CHEMICAL REACTION Process in which one or more substances are converted into new substances with different physical and chemical properties For example, a yellow solid precipitate, lead iodide (PbI2), forms from the mixture of two clear liquids, potassium iodide (KI) and lead nitrate (Pb(NO3)2).

2 H2(g) + O2(g)  2 H2O(l) Reactants Products CHEMICAL EQUATIONS “HYDROGEN GAS AND OXYGEN GAS REACT EXPLOSIVELY TO PRODUCE WATER” a. _________________________ INFORMATION 2. BALANCED CHEMICAL EQUATION WORD QUALITATIVE 2 H2(g) + O2(g)  2 H2O(l) Reactants Products Gives quantitative, as well as qualitative information.

COEFFICIENT: SUBSCRIPT: STATES: (s) = (l) = (g) = (aq) = Number IN FRONT of the formula 1. Tells number of particles (atoms/molecules) 2. 2 Cu + O2  2 CuO 2 Cu atoms + 1 oxygen molecule yields 2 copper oxide units SUBSCRIPT: Lower number to the right in a formula (2 Fe3O4 … subscripts are & ) STATES: (s) = (l) = (g) = (aq) = 3 4 solid liquid gas dissolved

WRITING CHEMICAL EQUATIONS 1. Write correct FORMULAS and physical states of ELEMENTS and COMPOUNDS. a. ELEMENTS: Element symbol (Fe), diatomic elements in pairs (Br2), also P4 for element phosphorus b. COMPOUNDS: Correct molecular or empirical formula 2. Balance the equation a. Law of Conservation of Mass SAME # OF ATOMS OF EACH ELEMENT ON BOTH SIDES OF EQUATION. b. Always adjust COEFFICIENTS, never SUBSCRIPTS. c. Coefficients in balanced eqn: IN LOWEST WHOLE # RATIO

Rules for Balancing Equations 1. Write correct formulas for all reactants and products For elements – use symbol: Iron = Fe Diatomic elements travel in pairs! H2, N2, O2, F2, Cl2, Br2, I2

a. To balance atoms of reactants and products, change ONLY the coefficients. b. Do NOT change the chemical formula to balance numbers of atoms.

WRITING CHEMICAL EQUATIONS 1. Carbon reacts with water to yield carbon monoxide (CO) and hydrogen. 2. When free bromine is added to dissolved sodium iodide (NaI), free iodine is produced, along with dissolved sodium bromide (NaBr). 3. Dissolved silver nitrate (AgNO3) reacts with copper to produce dissolved copper(II) nitrate (Cu(NO3)2 and silver.

4. Dissolved barium chloride (BaCl2) reacts with sodium sulfate (Na2SO4) to yield solid barium sulfate (BaSO4) and dissolved sodium chloride (NaCl). Remember the states of elements: Gases: Liquids: Solids: All the rest!

Al + O2  Al2O3 PRACTICE Fe2O3 + H2  Fe + H2O NaClO3  NaCl + O2 4. CO + O2  CO2 C2H2 + O2  CO2 + H2O Al(NO3)3 + Ca3(PO4)2  Ca(NO3)2 + AlPO4 Mg(OH)2 + H3PO4  Mg3(PO4)2 + H2O Ba(OH)2 + HCl  BaCl2 + H2O

BALANCING EQUATIONS Name_________________   1. N2 + O2  NO 2. Al + HCl  AlCl3 + H2 3. Ca(ClO3)2  CaCl2 + O2 4. Fe + H2O  Fe3O4 + H2 5. KI + Cl2  KCl + I2 6. NaCl + H2SO4  Na2SO4 + HCl 7. Ni(ClO3)3  NiCl3 + O2 8. C2H6 + O2  CO2 + H2O

________ 9. Al2O3  Al + O2 10. Ca3(PO4)2 + H2SO4  CaSO4 + H3PO4   10. Ca3(PO4)2 + H2SO4  CaSO4 + H3PO4 11. Al2(SO4)3 + Ca(OH)2  Al(OH)3 + CaSO4 12. NaHCO3  Na2CO3 + H2O + CO2 13. H2S + PbCl2  PbS + HCl 14. Fe + O2  Fe2O3 15. PbO2  PbO + O2 16. MnO2 + HCl  MnCl2 + Cl2 + H2O 17. Al(NO3)3 + H2SO4  Al2(SO4)3 + HNO3 ________

MOLE RELATIONS IN CHEMICAL EQUATIONS COEFFICIENTS IN BALANCED EQUATIONS GIVE THE MOLE RATIOS IN WHICH SPECIES REACT! MOLE RELATIONS IN CHEMICAL EQUATIONS Propane gas, C3H8, burns in oxygen to produce carbon dioxide and water vapor. C3H8(g) +  1 molecule + 5 molecules  3 molecules + 4 molecules C3H8 O2 CO2 H2O OR 1 mol C3H8 + 5 mole O2  3 mol CO2 + 4 mol H2O O2(g) CO2(g) + H2O(g)

a. If we start with 1.65 moles propane, C3H8, how many moles of oxygen are required to react with it? C3H8(g) + O2(g)  CO2(g) + H2O(g)

b. How many moles of carbon dioxide are formed? C3H8(g) + O2(g)  CO2(g) + H2O(g)

MOLE – MASS PROBLEMS If solid copper(III) oxide (Cu2O3) is decomposed into copper and oxygen by electrolysis, what mass of copper(III) oxide is required to produce 7.20 moles of copper? Cu2O3(s)  Cu(s) + O2(g)

2.65 grams of copper(III) oxide form how many moles of oxygen? Cu2O3(s)  Cu(s) + O2(g)

3. 100.0 grams of solid iron(III) oxide (Fe2O3) react with hydrogen gas to form water and iron. How many moles of water are produced in this reaction?   4. How many moles of hydrogen are required to form 3.67 moles of iron in the above reaction?

MASS-MASS PROBLEMS Solid sodium chlorate (NaClO3) is decomposed by heating to form oxygen and solid sodium chloride (NaCl). If 50.0 g of NaClO3 are decomposed, what mass of oxygen is formed? NaClO3(s)  NaCl(s) + O2(g)

2. Octane (C8H18) burns in air to form carbon dioxide and water 2. Octane (C8H18) burns in air to form carbon dioxide and water. What mass of oxygen is needed to form 150.g of carbon dioxide?

3. Iron reacts with chlorine gas to form solid iron(III) chloride (FeCl3). What mass of chlorine is needed to form 160. g of iron(III) chloride?

THE LIMITING REAGENT   An analogy:

1. Solid tetraphosphorus decoxide, P4O10, reacts with water to produce dissolved phosphoric acid (H3PO4). How many grams of phosphoric acid can be produced by the reaction of 0.720 mole of P4O10 with 2.28 moles of water?

2. Aluminum reacts with chlorine to form solid aluminum chloride (AlCl3). What mass of aluminum chloride is formed when 3.60 moles of aluminum reacts with 5.30 moles of chlorine?

2H2 (g) + 1O2 (g) 2H2O (l) 2 Molecules Water 2 Molecules H +1 molecule O2 + 2 Moles H2 + 1 Mole O2 2 Moles Water 4 g 32 g + 36 g Or 1 g + 8 g  9 g

Rules for Balancing Equations 2. Obey the LAW OF CONSERVATION OF MASS. Same number of each kind of atom on both sides of the equation. 25g + 25g + 50 g 50 g + 150 g ?g

How to Balance an Equation cont. c. Check your work by counting atoms of each element. d. Check to see that the coefficients are in the lowest whole number ratio. 2H2O (l) 2H2 (g) + 1O2 (g) 4 Hydrogen 4 Hydrogen 2 Oxygen 2 Oxygen e. SUBSCRIPTS: Lower numbers in a formula 4 Al2O3 1 Na2CO3 Subscripts: 2 & 3 Subscripts: 2, 1 & 3

Practice Balancing These Equations Ca + O2 CaO 2 1 2 1 Ca 1 Ca 2 O 1 O *Hint: Start by making the uneven side even. 2 O 2 O 1 Ca 2 Ca 2 Ca 2 Ca 2 O 2 O 1 Ca, 2 O 1 Ca, 2 O

Practice 1 CH4 + O2 CO2 + H2O 1 2 2 1 O 2 O 4 O 4 O 1 C 1 C 4 H 4 H *Hint: Start with the element that is split up: Oxygen. Then, make uneven side even. 1 O 2 O 4 O 4 O 1 C 1 C 4 H 4 H 1 C, 4 H, 4 O 1 C, 4 H, 4 O

Fe + Cl2 FeCl3 2 1 3 2 1 Fe 1 Fe 2 Cl 3 Cl 6 Cl 6 Cl 1 Fe 2 Fe 2 Fe Practice Fe + Cl2 FeCl3 2 1 3 2 1 Fe 1 Fe 2 Cl 3 Cl 6 Cl 6 Cl 1 Fe 2 Fe 2 Fe 2 Fe 2 Fe, 6 Cl2 2 Fe, 6 Cl2

2 HgO Hg + O2 2 1 Practice 1 3 2 Al + MnO Al2O3 + Mn 3 2 Al, 3 Mn, 1 O Br2+ NaI NaBr + I2 1 2 2 Br, 2 Na, 2 I 2 Br, 2 Na, 2 I Do these on own 2 HgO Hg + O2 2 1 2 Hg, 2 O 2 Hg, 2 O

Classification of Chemical Reactions 1. Synthesis 2. Decomposition 3. Single Replacement 4. Double Replacement 5. Combustion

Synthesis (Direct Combination) One or more elements or compounds combine to from a single product (compound). A B AB One Product Examples: Cu + O2 2 CuO 2 H2CO3 CO2 + H2O

AB A B Decomposition Examples: 2 2 H2O2 H2O + O2 2 2 3 KClO3 KCl + O2 A single compound is broken down into 2 or more simpler substances AB A B One Reactant Examples: 2 2 H2O2 H2O + O2 2 2 3 KClO3 KCl + O2

A BC AC B Single Replacement Examples: 2 Mg+ HCl MgCl2 + H2 2 2 One element replaces another from a compound A BC AC B Examples: 2 Mg+ HCl MgCl2 + H2 2 2 Cl2 + KI KCl + I2

Double Replacement (ionic) Ions in a solution combine to form a product that leaves the scene of the reaction AB CD AD CB Example: AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq)

More on Double Replacement Precipitate (s), gas (g) or water (H2O) will form AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq) Actual reaction: AgCl Ag+1 + Cl-1 Don’t dwell (do it in depth later) Spectator Ions: Na+1 & NO3-1

Combustion (burning) CxHy+ O2 CO2 + H2O C3H8 + O2 CO2 + H2O C2H2+ O2 Yes, James, FIRE! Produces light and heat CxHy+ O2 CO2 + H2O Balance C 1st, then H, then O (because it splits up) 1 C3H8 + O2 5 3 CO2 + H2O 4 1 C2H2+ O2 2.5 CO2 + H2O 2 1 * 2 C2H2 + 5 O2  4 CO2 + 2 H2O

Coefficients Must Be in Lowest WHOLE Number! 21/2 1 C2H2 + O2 CO2 + H2O 5 2 4 1 2 2 What number can you multiply 21/2 by to get the smallest whole number? 2! So, multiply the whole equation by 2 to get a properly balanced equation. 4 C, 4 H, 10 O 4 C, 4 H, 10 O

You try. Multiply by 2! 8 C, 2O H, 26 O 8 C, 2O H, 26 O 61/2 13 4 8 10 5 C4H10 + O2 CO2 + H2O 1 2 Multiply by 2! 8 C, 2O H, 26 O 8 C, 2O H, 26 O

Classification of Equations SYNTHESIS AB A B Ca S CaS DECOMPOSITION AB A B 2HgO 2Hg O2

Classification of Equations SINGLE DISPLACEMENT AB C A BC 2KCl Br2 Cl2 2KBr DOUBLE DISPLACEMENT AB CD AD BC CaSO4 BaCl2 CaCl2 BaSO4

Putting it all together 1. Write the ions and element symbols. 2. Rewrite the correct formulas. 3. Balance the equation. 4. Identify the type of reaction. BEFORE this they balance equation sheet (see star) then go back and ID type of equation Iron (II) sulfide + Hydrochloric acid Iron (II) sulfide + Hydrogen sulfide

1. Write the ions and element symbols Iron (II) sulfide + Hydrochloric acid Iron (II) sulfide + Hydrogen sulfide Fe+2S-2 + HCl Fe+2Cl-1 + H+1S-2

2. Rewrite the correct formula. Fe+2S-2 + HCl Fe+2Cl-1 + H+1S-2 FeS + HCl FeCl2 + H2S

4. Identify the type of reaction. 3. Balance the equation. 1 FeS + HCl FeCl2 + H2S 2 1 1 4. Identify the type of reaction. Insist on them writing oxidation states BEFORE formula. Double Replacement!

Try this one. Ca0 + HCl Ca+2Cl-1 + H2 1 + HCl Ca CaCl2 + H2 2 1 1 1. Write the ions and element symbols. 2. Rewrite the correct formulas. 3. Balance the equation. 4. Identify the type of reaction. Calcium + Hydrochloric acid Calcium chloride+ Hydrogen Ca0 + HCl Ca+2Cl-1 + H2 1 + HCl Ca CaCl2 + H2 2 1 1 Single Replacement!

Try this one. Zn+2 (OH)-1 Zn+2O-2 + H2O Zn(OH)2 ZnO + H2O 1 1 1 1. Write the ions and element symbols. 2. Rewrite the correct formulas. 3. Balance the equation. 4. Identify the type of reaction. Zinc hydroxide Zinc oxide+ water Zn+2 (OH)-1 Zn+2O-2 + H2O Zn(OH)2 ZnO + H2O 1 1 1 Maybe stop here and go on own with worksheet (depend on how they handle it). Decomposition!

Try this one. N20 + O20 N+2O-2 1 N2 + O2 NO 1 2 Synthesis! Nitrogen 1. Write the ions and element symbols. 2. Rewrite the correct formulas. 3. Balance the equation. 4. Identify the type of reaction. Nitrogen Nitrogen oxide + Oxygen N20 + O20 N+2O-2 1 N2 + O2 NO 1 2 Synthesis!

Activity Series of the Elements: Table L Metals Li Rb K Ba Sr Ca Na Mg Al Mn Zn Cr Fe Cd Co Ni Sn Pb H2 Sb Bi Cu Hg Ag Pt Au Nonmetals F2 Cl2 Br2 I2 Replaces H from acids Replaces H from water Most Active Most Active Least Active Least Active Metals replace metals or H Nonmetals replace nonmetals *REPLACE FROM OWN COLUMN

Making Predictions: Single Replacement Rxn 1. Write symbol and ions (for compounds) and predict products. 2. Rewrite correct formulas. 3. Use activity series to tell if rxn occurs and why. 4. Balance equation. Pepsi commercial Aluminum + Nickel (II) chloride ?

1. Write symbols & ions and predict products. Aluminum + Nickel (II) chloride ? Al0 + Ni+2Cl-1 Al+3Cl-1 + Ni0 2. Rewrite correct formulas. Al + NiCl2 AlCl3 + Ni

3. Use the activity series to tell if the rxn occurs and why. Yes, Al is more active than Ni. 2 Al + NiCl2 3 2 AlCl3 + Ni 3 4. Balance equation.

Now try this one. Ca0 + Co+3(NO3)-1 Ca+2(NO3)-1 + Co0 3 Ca(NO3)3 + Co 1. Write symbol and ions (for compounds) and predict products. 2. Rewrite correct formulas. 3. Use activity series to tell if rxn occurs and why. 4. Balance equation. Calcium + Cobalt (III) nitrate ? Ca0 + Co+3(NO3)-1 Ca+2(NO3)-1 + Co0 3 Ca(NO3)3 + Co 2 3 Ca + Co(NO3)3 2 Yes, Ca is more active than Co.

Now try this one. Br20 + Rb+1I-1 Rb+1Br-1 + I20 1 2 RbBr + I2 1 Br 1. Write symbol and ions (for compounds) and predict products. 2. Rewrite correct formulas. 3. Use activity series to tell if rxn occurs and why. 4. Balance equation. Bromine + Rubidium Iodide ? Br20 + Rb+1I-1 Rb+1Br-1 + I20 1 2 RbBr + I2 1 Br + RbI 2 Yes, Br is more active than I.

Making Predictions: Double Replacement Rxn Double Replacements will only complete when one or more of these events occur: 1. Water forms (H2O) 2. A gas forms (g) 3. A precipitate (s) forms Do “Chapter 9 Double Replacement Reactions” first two together, rest on own.

Let’s try a couple Does the reaction occur? Does the reaction occur? Ba(OH)2 (aq) + H2SO4(aq) BaSO4(aq) + H2O(l) Does the reaction occur? YES; water is formed. What are the spectator ions? (The ions not involved in forming water, gas, or precipitate) Ba+2 & SO4-2 Ca3(PO4)2(aq) + NaNO3(aq) Na3(PO4)2(aq) + CaNO3(aq) Does the reaction occur? No; no water, gas or precipitate is formed.

Potassium chromate + copper(II) hydroxide 1. Write symbols & ions and predict products. Rewrite correct formulas and look up states of products on Table C. K+1 (CrO4)-2 + Cu+2(OH)-1 Cu+2(CrO4)-1 + K+1(OH)-1 K2 (CrO4) + Cu(OH)2 Cu(CrO4)2 (s) + K(OH) (aq) insoluble on Table C soluble on Table C

1 2 NO NO YES! THE RXN OCCURS! 3. Balance equation. Potassium chromate + copper(II) hydroxide 3. Balance equation. 4. Does reaction occur? Does water form? Does a gas (g) form? Does a precipitate (s) form? 1 2 K2CrO4 + Cu(OH)2 CuCrO4 (s) + KOH (aq) NO NO YES! THE RXN OCCURS! Do “Double Replacement Reactions” predicting Then single and double replacement reactions predicting

Writing equations from words Write the equation for the production of oxygen gas and potassium chloride from the breakdown of potassium chlorate. 1. Potassium chlorate breaks down to form potassium chloride & oxygen K+1Cl-1 + O2 K+1(ClO3)-1 2. Rewrite the correct formulas. KCl + O2 K(ClO3) 3. Balance the equation by changing the coefficients. KCl + O2 K(ClO3) 2 3

Barium hydroxide reacts with carbon dioxide to form barium carbonate and water. Barium hydroxide reacts with carbon dioxide to form barium carbonate & water Ba+2(OH)-1 + CO2 Ba+2(CO3)-2 + H2O(l) Ba(OH)2 + CO2 BaCO3 + H2O(l) Ba(OH)2 + CO2 BaCO3 + H2O(l) 1

CaC2 + H2O(l) + C2H2(g) Ca+2(OH)-1 CaC2 + H2O (l) Ca(OH)2 + C2H2(g) 2 Calcium carbide, CaC2, reacts with water to produce calcium hydroxide & ethyne gas, C2H2. Calcium carbide reacts with water to produce calcium hydroxide & ethyne gas CaC2 + H2O(l) + C2H2(g) Ca+2(OH)-1 CaC2 + H2O (l) Ca(OH)2 + C2H2(g) CaC2 + H2O (l) Ca(OH)2 + C2H2(g) 2 1

Classification of Equations SYNTHESIS AB A B Ca S CaS DECOMPOSITION AB A B 2HgO 2Hg O2

Classification of Equations SINGLE DISPLACEMENT AB A BC C 2KCl Br2 Cl2 2KBr DOUBLE DISPLACEMENT AB CD AD BC CaSO4 BaCl2 CaCl2 BaSO4

Practice 1 CH4 + O2 CO2 + H2O 1 2 2 1 C 1 C 4 H 2 H 2 O 3 O 4 O 4 O *Hint: Don’t make a move until you find the uneven side. 2 O 3 O 4 O 4 O 1 C 1 C 4 H 4 H 1 C, 4 H, 4 O 1 C, 4 H, 4 O

Practice 2 1 Na + H2O NaOH + H2 2 1 2 1 Na 1 Na 2 H 3 H 4 H 4 H 1 Na

Practice 6 C, 16 H, 20 O 6 C, 16 H, 20 O 6 8 2 C3H8 + O2 CO2 + H2O 1 1 10 1 C 3 C 6 C 6 C 2 H 16 H 16 H 16 H 2 O 20 O Do together 20 O 20 O 6 C, 16 H, 20 O 6 C, 16 H, 20 O

Practice 1 2 Ba(OH)2 + HCl BaCl2 + H2O 1 1 2 1 Ba 1 Ba 2 O 1 O 2 O 2 O 1 Ba, 4 H, 2O, 2Cl 1 Ba, 4 H, 2O, 2Cl

Practice 3 2 1 Na3PO4 + Al2(SO4)3 Na2SO4 + AlPO4 2 1 3 Na 2 Na 6 Na 6 Ba, 2P, 20 O, 2 Al, 3 S 6 Ba, 2P, 20 O, 2 Al, 3 S

Practice 2 Ca(NO3)2 + KCl KNO3 + CaCl2 1 1 2 2 3 1 3 Al(OH)3 + CaSO4 Al2(SO4)3 + Ca(OH)2 2 Al, 12 O, 3 H, 3 Ca, 1 S 2 Al, 12 O, 3 H, 3 Ca, 1 S