Regents Chemistry Unit 3- Bonding, Moles & Stoichiometry Study Guide & Pre-Test KEY

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1 Name: Regents Chemistry Unit 3- Bonding, Moles & Stoichiometry Study Guide & Pre-Test KEY Focus Questions for the Unit: How are compounds different... from elements?... from mixtures? What role do valence electrons play in bonding? How does valence electron behavior determine bond type? What properties of compounds are determined by bond type? What notation and nomenclature are used by chemists to describe compounds? What is the significance of a chemical formula? How are chemical equations used to illustrate chemical reactions? How are moles used in chemistry? Key Words to Know: (Check off the ones that you know and study the other ones!) Vocab Topic 1: Reviewing Compounds o Conservation of Mass o Reactant vs. Product o Balanced Equation o Coefficient vs. Subscript o Element vs. Compound o Endothermic vs. Exothermic o Symbol Topic 2: Chemical Properties Using the Periodic Table o Ion o Cation o Anion Topic 3: Ionic Bonding o Ionic bonding o Valence electrons o Octet rule o Lewis dot o Cation vs. Anion o Chemical Formula Topic 4: Covalent (Molecular) Bonding o Covalent (Molecular) Bonding o Molecule o Molecular Formula o Multiple Bond (Double Bond, Triple Bond) o Single Bond o Electron Pairs Topic 5: Polyatomic Ions o Monatomic ions o Polyatomic ions Topic 7: Moles & Stoichiometry o Mole ratio o Mole o Molar Mass (Formula Mass, Gram Formula Mass) Definitions/Related Words Reference Tables Used: Tables E, S, T, & Periodic Table

2 Vocabulary Practice: Anion Balanced Equation Cation Chemical Formula Coefficient Compound Conservation of Mass Covalent Bonding Electron Pair Endothermic Exothermic Ionic Bonding Lewis Dot Molar Mass Mole Mole ratio Molecular Bonding Molecular Formula Molecule Monatomic Ion Multiple Bond Ion Octet rule Polyatomic Ion Product Reactant Single Bond Subscript Valence electrons Compound Subscript_ Coefficient Exothermic Endothermic Polyatomic Ion_ Product 1. Substance in which the atoms exist in a fixed ratio 2. The number that indicates the number of atoms present 3. The number that indicates the number of units or molecules of that substance 4. Process in which energy is released (occurs when bonds are formed) 5. Process in which energy is absorbed (occurs when bonds are broken) 6. A covalently bonded group of atoms that have a net electric charge 7. Substance formed as a result of a chemical reaction, shown to the right of the arrow. Chemical Formula 8. Combination of symbols and subscripts, used to represent the ratio of atoms of a substance Reactant 9. A substance that a chemical reaction occurs upon, shown to the left of the arrow. Molecule_ Covalent Molecular Molar Mass Lewis Dot Cation Anion_ 10.The smallest unit of a covalently bonded substance that has the properties of that substance 11a. Bond formed by the sharing of valence electrons between 2 nonmetallic nuclei. 11b. Bond formed by the sharing of valence electrons between 2 nonmetallic nuclei. 12. The mass of one mole of a substance 13. A type of diagram Chemist s use to show how atoms bond 14. An atom that has lost electrons to obtain a positive charge 15. An atom that has gained electrons to obtain a negative charge Valence electrons 16. The outer electrons of an atom that can be exchanged or shared with other atoms. Single Bond 17. Occurs when only one pair (2 electrons) are shared between two nuclei. Multiple Bond_ Monatomic Ion Octet Rule Electron Pair Ionic 18. Occurs when more than 1 pair (4 or more electrons) are shared between two nuclei 19. A single element with a positive or negative charge due to the loss or gain of e The stable valence electron configuration of 8 electrons, which every element tries to obtain by bonding; the driving force behind why atoms bond the way they do 21. Represented by a single line in a Lewis diagram of a covalent compound 22. Bond formed by a transfer of valence electrons from a metal to a nonmetal Molecular Formula 23. A specific type of chemical formula that tells exactly how many of each atom are in a substance, not just the ratio of these atoms _Balanced Equation Cons. of Matter _ Mole Mole ratio 24. An equation that has the correct coefficients in place in order to demonstrate conservation of mass. _25. The idea that matter can be changed, but an equation should always start and end with the same number and type of each atom. 26. A measure of the number of particles in a substance, which we use to calculate the number of grams of a substance 27. The ratio of moles of atoms needed to complete a chemical reaction, depicted by a balanced equation

3 2 Ions 28. An atom that has either lost or gained electron(s).

4 Topic 1: Review 1. Which substance can not be decomposed (broken down) by a chemical change? (1) ammonia (3) ammonium nitrate (2) copper (4) water 2. When a metal atom becomes an ion, it loses (gains/loses) electrons and has a _+ (+/ ) charge. The ion is called a(an) cation (anion/cation). 3. When a non-metal atom becomes an ion, it gains (gains/loses) electrons and has a (+/ ) charge. The ion is called a(an) anion (anion/cation). Topic 2: Chemical Properties Using the Periodic Table 1. As an atom becomes an ion, its mass number (1) decreases (2) increases (3) remains the same 2. The following equation represents the formation of a (1) fluoride ion, which is smaller in radius than a fluorine atom (2) fluorine atom, which is smaller in radius than a fluoride ion (3) fluoride ion, which is larger in radius than a fluorine atom (4) fluorine atom, which is larger is radius than a fluoride ion 3. What is the total number of electrons in a Cu + ion? (1) 28 (2) 29 (3) 30 (4) After a neutral sulfur atom gains two electrons, what is the resulting charge of the ion? What is the total number of electrons in a Cr 3+ ion? (1) 18 (2) 21 (3) 24 (4) How many electrons are contained in an Au 3+ ion? (1) 76 (2) 79 (3) 82 (4) How are neutral atoms converted into cations? Electrons are lost. 8. How are neutral atoms converted into anions? Electrons are gained. 9. Metals usually form what type of ions? Cations 10. Nonmetals usually form what type of ions? Anions 11. When combining with non-metallic atoms, metallic atoms will _ lose _ electrons to 3

5 form positive (positive, negative) ions. (lose, gain) 4

6 12. Sulfur atoms can form anions with a _- 2 charge in order to get a full octet. (cations, anions) (+, - ) (1,2,3,4) 13. When an atom becomes an anion, what happens to its radius? Gets bigger 14. When an atom becomes a cation, what happens to its radius? Gets smaller 15. For each of the following pairs, circle the atom or ion having the larger radius. a. S or O c. Na 1+ or K 1+ e. S 2 or O 2 b. Ca or Ca 2+ d. Na or K f. F or F Draw Lewis dot structures for the following: a. sulfide anion b. magnesium cation c. bromide anion d. P 3- [ S ] - 2 [Mg] 2+ [ P ] -3 [ Br ] Draw Bohr diagrams for the following (include protons and neutrons in nucleus): a Ca S b. p + = 20 n 0 = p + = 16 n 0 = The ions which are normally formed from K and Cl have the same electron configuration. What is it? This is the same configuration as which noble gas? Ar How are the two ions different? 5

7 They have a different number of protons and neutrons in the nucleus and different charges (K +1, Cl -1 ) 6

8 19. Give the symbol for one (1) cation and one (1) anion that have the same electron configuration as the noble gas, krypton. Cations: Rb +1, Sr +2, Y 3+ Anions: As 3-, Se 2-, Br Fill in the following table: Symbol # protons # neutrons # electrons atomic # mass # 59 Co O Ga Cl Topic 3: Ionic Bonding Write the names from the formula: 1. KBr potassium bromide 2. Al 2 O 3 aluminum oxide 3. MgS magnesium sulfide Write the formula from the name: 4. Sodium Phosphide 5. Barium Chloride 6. Calcium Nitride 7. Gold (III) Sulfide 8. Chromium (II) Nitride Na 3 P BaCl 2 Ca 3 N 2 Au 2 S 3 Cr 3 N 2 Na 1+ P 3- Ba 2+ Cl 1- Ca 2+ N 3- Au 3+ S 2- Cr 2+ N 3-9. What is the IUPAC name for the compound FeS? S = -2, therefore Fe = +2 for a 1:1 ratio (1) iron (II) sulfate (3) iron (II) sulfide (2) iron (III) sulfate (4) iron (III) sulfide 7

9 10. In which compound is the ratio of metal ions to nonmetal ions 1 to 2? (1) calcium bromide (CaBr 2 ) (3) calcium phosphide (Ca 3 P 2 ) (2) calcium oxide (CaO) (4) calcium sulfide (CaS) 8

10 11. In the formula X 2 O, the symbol X could represent an element in Group: (1) 1 (3) 15 Since O= -2, X must be +1 each (2) 2 (4) Which formul a represents copper (I) oxide? Cu = +1 and O = -2 (1) CuO (2) CuO 2 (3) Cu 2 O (4) Cu 2 O Which element, represented by X, reacts with fluorine to produce the compound XF 2? (1) aluminum (3) magnesium Since F = -1, X must be +2 (2) argon (4) sodium 14. The compound XCl is classified as ionic if X represents the element (1) H (3) Rb Must be a metal with a +1 charge! (2) I (4) Br 15. What is the chemical formula for iron (III) oxide? (1) FeO (3) Fe 3 O Fe = +3 and O = -2 (2) Fe 2 O 3 (4) Fe 3 O An ionic compound is formed when there is a reaction between the elements (1) strontium and chlorine Must be a metal with a nonmetal! (2) hydrogen and chlorine (3) nitrogen and oxygen (4) sulfur and oxygen 17. Which formula represents an ionic compound? (1) H 2 (3) CH 3 OH Must be made of cations & anions! (2) CH 4 (4) NH 4 Cl 18. A barium atom attains a stable electron configuration when it bonds with (1) one chlorine atom (Ba would only lose 1 e - ) Barium wants to lose 2 electrons to be stable (2) two chlorine atoms (Ba would lose 2 e - ) (3) one sodium atom (metal does not want to react with metal) (4) two sodium atoms (metal does not want to react with metal) Topic 4: Covalent (Molecular) Bonding 1. The nitrogen atoms in a molecule of N 2 share a total of (1) one pair of electrons (2) one pair of protons (3) three pairs of electrons (4) three pairs of protons 2. It is possible for bonds to be single, double or triple covalent. Which molecule contains 3 single covalent bonds? (1) H 2 (3) I 2 (2) NH 3 (4) H 2 O 9

11 3. When covalent compounds bond, they share valence electrons. a. If one pair of valence electrons are shared between two atoms, this is called a single covalent bond. It represents a total of 2 (how many?) total shared valence electrons. b. If a total of four valence electrons are shared between two atoms, this is called a double covalent bond. It represents 2 (how many?) pairs of shared valence electrons. c. If three pairs of valence electrons are shared between two atoms, this is called a triple covalent bond. It represents a total of 6 (how many?) total shared valence electrons. Topics 3 & 4: Ionic & Covalent Bonding 1. Which compound has both ionic and covalent bonding? Must have a metal & polyatomic ion! (1) CaCO 3 (3) CH 3 OH (2) CH 2 Cl 2 (4) C 6 H 12 O 6 2. The chemical bonding in sodium phosphate, Na 3 PO 4, is classified as (1) ionic, only (3) both covalent and ionic (2) metallic, only (4) both covalent and metallic 3. Two categories of compounds are Molecular = covalent! (Two terms that mean the same thing!) (1) covalent and molecular (3) ionic and molecular (2) covalent and metallic (4) ionic and metallic 4. Which type of substance can conduct electricity in the liquid phase but not in the solid phase? (1) ionic compound (3) metallic element Choices 2 & 4 never conduct, (2) molecular compound (4) nonmetallic element Choice 3 conducts as a solid 5. The bonds in BaO are best described as (1) covalent, because valence electrons are shared (2) covalent, because valence electrons are transferred (3) ionic, because valence electrons are shared (4) ionic, because valence electrons are transferred 6. Which compound contains both ionic and covalent bonds? Metal & polyatomic ion (1) ammonia (3) sodium nitrate (2) phosphate (4) potassium chloride 7. Tell whether the following are ionic, molecular (covalent), both, or neither. Name those that are NOT molecular. a.) Ag 3 (PO 4 ) b.) Mg c.) Rb(CO 3 ) 2 d.)ph 3 Both Neither Both Molecular silver phosphate magnesium rubidium carbonate e.) FeCl 2 f.) ClBr g.) Br 2 h.) Al 2 O 3 Ionic Molecular Covalent Ionic Iron (II) chloride bromine aluminum oxide 10

12 8. Draw electron dot (Lewis) structures for the following compounds. a.) I 2 b.) O 2 c.) PCl 3 OR OR OR I I For each diagram, only the valence electrons are shown! For I 2, there is one single bond, signifying one shared pair of valence electrons (a total of 2 valence electrons being shared) between each I atom. For O 2, this is one double bond, signifying two shared pairs of valence electrons (a total of 4 valence electrons being shared) between each O atom. For PCl 3, there are three single bonds. Each single bond signifies one shared pair of valence electrons (a total of 2 valence electrons being shared) between the P atom and one of the Cl atoms. 9. For each structure above, describe the electrons. Which electrons are depicted (all or just valence)? Describe how many bonds are present and how many electrons are in each bond. See above! 10. Why are electron dot (Lewis) structures used to depict bonding instead of electron shell (Bohr) diagrams? Electron dot (Lewis) structures show only the valence electrons, whereas electron shell (Bohr) diagrams show all electrons. Since only the valence electrons are used in bonding, Lewis structures are more useful in depicting bonding. 11. Draw Lewis dot structures for the following (Remember to first determine whether they are ionic or molecular (covalent)!!) a.) Na 2 O b.) CH 4 c.) CaCl 2 ionic covalent ionic [Na] +1 [ O ] -2 [Na] +1 [ Cl ] -1 [Ca] +2 [ Cl ] -1 d.) NH 3 e.) N 2 f.) Al 2 S 3 covalent covalent ionic OR [ S ] -2 [Al] +3 [ S ] [Al] +3 [ S ] -2

13 12. Explain how you know if something bonds ionically, molecularly, both, or neither. You need to determine the types of atoms being bonded. If it is a metal/nonmetal it is ionically bonded, if it is two nonmetals it is a molecular bond, if it is two metals it is neither ionic or covalent, it is metallic, and if it has a polyatomic ion in it, it is both ionic and molecular because the elements in the polyatomic ion are bonded to one another covalently, but will bond with a third element ionically. 13. How many ions are formed when one unit of Ca(NO 3 ) 2 is dissolved in water? What are the ions? 3 Total Ions are formed- 1 Ca 2+ ion and 2 (NO 3 ) 1- ions 14. How many ions are formed when one unit of Al 2 (SO 4 ) 3 is dissolved in water? What are they? 5 Total ions are formed- 2 Al 3+ ions and 3 (SO 4 ) 2- ions 15. When 1 mole of AlCl 3 is dissolved in water, how many moles of Cl - are formed? EXPLAIN! 1 mole of AlCl 3 is 1 unit of AlCl 3 so it will form 3 Cl 1- ions. Each of these is 1 mole of Cl 1- ions 16. When 2 mole of SO 2 is dissolved in water, no ions are formed because it is not ionic. Describe what will happen to the SO 2 when it is dissolved. The covalently bonded SO 2 will break up into separate SO 2 molecules, but not into S & O. No new particles are formed, just smaller pieces with the same composition. 17. Multiple Choice: If element X is an alkali metal from group 1 and element Y is a non-metal from group 16, a compound formed between the two might have the formula: 1.) X 2 Y 2.) XY 2 3.) X 2 Y 2 4.) XY EXPLAIN your choice: An element in group 1 would have a +1 charge and an element from group 16 would have a 2- charge. In order to make these charges equal to zero and have a neutral compound, you would need 2 X s (total of +2) and 1 Y (total of -2). 18. Multiple Choice: If element X is an alkaline earth metal from group 2 and element Y is a non-metal from group 16, a compound formed between the two might have the formula: 1.) X 2 Y 2.) XY 2 3.) X 2 Y 2 4.) XY EXPLAIN your choice: An element in group 2 would have a +2 charge and an element from group 16 would have a 2- charge. In order to make these charges equal to zero and have a neutral compound, you would need one of each element. 19. Multiple Choice: If element X is an alkali metal from group 1 and element Y is a non-metal from group 17, a compound formed between the two might have the formula: 1.) X 2 Y 2.) XY 2 3.) X 2 Y 2 4.) XY EXPLAIN your choice: An element in group 1 would have a +1 charge and an element from group 17 would have a 1- charge. In order to make these charges equal to zero and have a neutral compound, you would need one of each element. 12

14 20. Fill in the following chart, which compares characteristics of both ionic and covalent bonding. Defining Characteristic Ionic Covalent (Molecular) Type of atoms involved? Metal & Nonmetal 2 Nonmetals Describe how the valence electrons are interacting in the bond Does it have electrical conductivity as a solid? They are transferred from metal (loses) to nonmetal (gains) No They are shared No Does it have electrical conductivity when/if dissolved in water? What phase or phases do the compounds formed tend to be in at STP? Yes! The more ions there are in the chemical formula, the more conductive it is! Solids No Liquid or Gases Relative melting/boiling point temperature: High or Low? High MP/BP Low MP/BP Particle attractions are: Stronger or Weaker? Stronger Weaker Describe how you would draw Lewis Structures. (Feel free to draw an example!) Describe how you would name one of these compounds. First, draw the Lewis structures for the atoms involved prior to bonding. Then draw arrows to show how e- are transferred. Rewrite these atoms as ions with brackets and charges (no electrons around metals, 8 electrons around nonmetals). Name the cation first. If it is a transition metal, use a roman numeral to indicate the correct charge. Next, name the anion. If it s a nonmetal, give it an -ide ending. Use Ref. Table E for any polyatomic ions. Remember that sometimes these will not be in parentheses! 13 First, draw the Lewis structures for the atoms involved prior to bonding. Then draw loops around unpaired electrons to show how e- are shared. Rewrite these atoms showing the correct number of electrons shared between them, remember that one line= 2 electrons. Check your answer to make sure you have 8 electrons around each atom. (Hydrogen will only have 2 e - ) NO NAME NECESSARY!!

15 Topic 5: Polyatomic Ions 1. Which formula represents lead (II) chromate? (1) PbCrO 4 (3) Pb 2 CrO 4 (2) Pb(CrO 4 ) 2 (4) Pb 2 (CrO 4 ) 3 2. Which formula represents barium phosphate? (1) BaPO 4 (3) Ba 2 (PO 4 ) 3 (2) Ba 3 (PO 4 ) 2 (4) Ba 3 PO 8 3. Which polyatomic ion contains the greatest number of oxygen atoms? (1) acetate (3) hydroxide (2) carbonate (4) peroxide 4. Given the formula: Al 2 (SO 4 ) 3 a) How many sulfate ions are shown? 3 b) How many total ions? 5 c) How many atoms Al? 2 S? 3 O? 12 d) Describe how the atoms are bonded together. The nonmetallic sulfur and oxygen atoms are bonded to one another covalently, forming a negatively charged particle, which will then bond ionically to aluminum. Write the formula from the name: 5. Sodium Phosphate Na 3 (PO 4 ) 6. Ammonium Fluoride NH 4 F 7. Aluminum Carbonate Al 2 (CO 3 ) 3 8. Iron (III) Hydroxide Fe(OH) 3 9. Copper (II) Nitrate Cu(NO 3 ) 2 Write the name from the formula: 10. Al 2 (SO 4 ) 3 aluminum sulfate 11. (NH 4 ) 3 (PO 4 ) ammonium phosphate 14

16 12. Fe 2 O 3 iron (III) oxide 13. Ca(NO 3 ) 2 calcium nitrate 15

17 Topic 6: Understanding Chemical Equations 1. A balanced equation representing a chemical reaction can be written using (1) chemical formulas and mass numbers (2) chemical formulas and coefficients (3) subscripts and mass numbers (4) mass numbers and coefficients 2. a. Define endothermic. Endothermic means that heat energy is being absorbed, so heat is a reactant in a chemical reaction. This occurs when bonds between atoms are broken. b. Define exothermic. Exothermic means that heat energy is being released, so heat is a product in a chemical reaction. This occurs when bonds are formed between atoms. 3. In an exothermic reaction (1) energy is a product and the surrounding temperature increases (2) energy is a product and the surrounding temperature decreases (3) energy is a reactant and the surrounding temperature increases (4) energy is a reactant and the surrounding temperature decreases Base your answers on Questions #4-12 on the following equation: _1_ Ca (s) + _2 H 2 O (l) _1_ Ca(OH) 2 (aq) + _1 H 2 (g) + heat 4. Balance the equation. (Rewrite H 2 O as HOH this will help you!) 5. Why do we balance equations? We balance equations to show conservation of mass/matter, that even though we may change the arrangement of the atoms, we have to start and end with the same amount and type of each. 6. What are the reactants? Ca and H 2 O 7. Which are the products? Ca(OH) 2 and H 2 8. What does (s) mean? solid 9. What does (l) mean? liquid 10. What does (aq) mean? aqueous (dissolved in water) 11. What does (g) mean? gas 12. Is the reaction described exothermic or endothermic? How do you know from the equation? Exothermic because heat is a product, so heat is being released as a result of the reaction. 16

18 13. Balance the following equations. Draw particle diagrams for a-c. a. 2 Al(OH) 3 (s) 1 Al 2 O 3 (s) + 3 H 2 O (l) = Al = O = H b. 1 Ca (s) + 2 HCl (aq) 1 CaCl 2 (aq) + 1 H 2 (g) = Ca = H = Cl c. 2 Fe (s) + 3 S (s) 1 Fe 2 S 3 (s) = Fe = S d. 1 C 4 H 8 (g) + 6 O 2 (g) 4 CO 2 (g) + 4 H 2 O (g) e. 2 K 3 (PO 4 ) (aq) + 3 Mg(NO 3 ) 2 (aq) 1 Mg 3 (PO 4 ) 2 (aq) + 6 KNO 3 (aq) f. 2 Al (s) + _ 3 Cu(SO 4 ) (aq) 1 Al 2 (SO 4 ) 3 (aq) + 3 Cu (s) g. 3 Ag(NO 3 ) (aq) + 1 AlBr 3 (aq) 3 AgBr (s) + 1 Al(NO 3 ) 3 (aq) h. 2 CO(g) + 1 O 2 (g) 2 CO 2 (g) 17

19 1. What is the gram-formula mass of Ca 3 (PO 4 ) 2? (1) 248 g/mol (3) 279 g/mol (2) 263 g/mol (4) 310. g/mol 2. A 1.0-mole sample of krypton gas has a mass of (1) 19 g (3) 39 g (2) 36 g (4) 84 g 3. If the mass of one mole of H 2 X is 18 grams, then X must represent which element? EXPLAIN!!! H has a mass of 1 g. If there are 2 H s, the total mass of H is 2 g. The whole compound has a mass of 18 grams, so 18 (total mass)-2(mass of H), leaves 16 g of the total mass that must come from X. There is only 1 X, so each X has a mass of 16 g. Using the Periodic Table of Elements, this must be Oxygen. 4. What is the molar mass of AlBr3? Al = 27, Br = 79.9 X , = g 5. What is the gram formula mass of CO2? C = 12, O = 16 X 2 = 32, = 44 g 6) What is the gram formula mass of CaCl2? Ca = 40.1, Cl X 35.5 X 2 = 71, = g 7. What is the mass of 4 moles of CO 2? SHOW WORK! GFM CO 2 =44g/mol 4 moles = mass = 176 g CO g/mol 8. What is the mass of 0.4 moles of H 2 O? SHOW WORK! GFM H 2 O=18g/mol. 4 moles = mass = 7.2 g H 2 O 1 18 g/mol 9. a. How many moles in 60.0 grams of Ca(NO 3 ) 2? GFM Ca(NO 3 ) 2 =164g/mol moles = 60 g =.37 moles of Ca(NO3)2 164 g/mol 18

20 b. How many grams of Ca(NO 3 ) 2 in 0.23 moles of Ca(NO 3 ) 2? GFM Ca(NO 3 ) 2 =164g/mol.23 moles = mass Mass = 37.7 g Ca(NO 3 ) g/mol c. How many grams in 12 moles of P 2 O 5? GFM P 2 O 5 =142g/mol 12 moles = mass Mass = 1704 g P2O5 d. How many moles in 37.4 grams of P 2 O 5? g/mol GFM P 2 O 5 =142g/mol Moles = 37.4 g Moles =.26 mole P2O5 142 g/mol 10. Some dry chemicals can be used to put out forest fires. One of these chemicals is NaHCO 3. When NaHCO 3 (s) is heated, one of the products is CO 2 (g), as shown in the balanced equation below. 2NaHCO 3 (s) + heat Na 2 CO 3 (s) + H 2 O (g) + CO 2 (g) Determine the total number of moles of CO 2 (g) produced when 7.0 moles of NaHCO 3 (s) is completely reacted. 1 = 2 X = 3.5 moles CO2 X Given the balanced equation representing a reaction: 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O Determine the total number of moles of oxygen that react completely with 8.0 moles of C 2 H 6. 7 = 2 X = 28 moles O2 X 8 12 Determine the mass of 5.20 moles of C 6 H 12 (gram-formula mass = 84.2 grams/mole) 5.20 moles = mass mass = g g/mol 13. The coefficients in balanced equations show the ratio of moles that react. For example, the reaction of phosphorous with oxygen is written as: 4 P + 5 O 2 2 P 2 O 5 This means that the ratio of reactants and products is 4 P : 5 O 2 : 2 P 2 O 5 19

21 Given the following reaction C 3 H O 2 3 CO H 2 O a.) What is the ratio of moles of C 3 H 8 to moles of O 2 required for the reaction? 1 moles C 3 H 8 : 5 moles O 2 b.) If you start with 8.0 moles of C 3 H 8, how many moles of O 2 would you need for the C 3 H 8 to react completely? Show your work! 1 = 5 X = 40 moles O2 8 X c.) If you start with 0.42 moles of C 3 H 8, how many moles of O 2 would you need for the C 3 H 8 to react completely? Show your work! 1 = 5 X = 2.1 moles O2.42 X d.) If you start with 2.0 moles of C 3 H 8, how many moles of H 2 O will be formed? Show your work! 1 = 4 X = 8 moles of H2O 2 X e.) If you obtain 5.3 moles of CO 2, how many moles of O 2 did you start with? Show your work! 3 = 5 X = 8.83 moles O2 5.3 X 20