Assignment #1: Redox Reaction Skill Drills

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1 Assignment #1: Redox Reaction Skill Drills Skill #1 Assigning Oxidation Numbers (Text Reference: p ) All elements have an oxidation number of 0. In compounds, oxidation numbers add up to 0. o Group 1 elements are +1 in all compounds. o Group 2 elements are +2 in all compounds. o F is always -1 in compounds. o H is usually +1, and if so, will be first written in the chemical formula. o O is almost always -2, exceptions: H 2 O 2 and OF 2 o In compounds using polyatomic ions, the first and middle elements all have + oxidation states. Sulfur has 5 oxidation states: -2, 0, +2, +4, +6 1.) Which substance listed below has sulfur with an oxidation state of 0? How do you know? 1. H 2 S 2. S 3. SO 3 4. SO 2 S isn t in a compound it s a free element! 2.) In the compound Na +1 2S +2 2O 2 3, does S have a + or oxidation state? + What is the oxidation number of S in each of the following substances? 3.) H 2 S -2 5.) SO ) SO ) S 0 6.) Na 2 S 2 O 3 +2 Chlorine has six possible oxidation states that it uses in bonding situations: -1, 0, +1, +3, +5, +7 What is the oxidation number of Cl in each of the following substances? 8.) HClO ) HClO ) NaCl -1 9.) HClO ) HClO ) Cl 2 0 Hydrogen has three oxidation states: -1, 0, +1 What is the oxidation number of H in each of the following substances? 14.) LiH ) H 2 O ) H 2 S ) H 2 0 Oxygen is usually -2 in compounds, but may be -1 or +2 in weird situations What is the oxidation number of O in each of the following substances? 18.) H 2 O ) NaOH ) O ) H 2 SO ) OF ) Na 2 O 2-1 Nitrogen has an amazing nine oxidation states! -3, -2, -1, 0, +1, +2, +3, +4, +5 Assign an oxidation state to N in each compound: 24.) NO ) HNO ) Li 3 N ) NH 3-3

2 SCORE YOURSELF ON THIS DRILL: /27 IF you missed more than 4, you should do Assignment #1A to get more practice on SKILL #1!! Assignment #1: Redox Reaction Skill Drills (cont d) Skill #2 Identifying Redox Reactions (Text Reference: p ) In all reactions, both mass and charge must be conserved (maintained). If an equation involves a free element (an element by itself), it is a redox reaction. Double replacement reactions are NEVER redox, but the other 4 types USUALLY are. 1.) Which equation is an example of an oxidation-reduction reaction? Two answers! (oops!) 1. C 3 H O 2 3 CO H 2 O 3. Cu + 2AgNO 3 Cu(NO 3 ) 2 + 2Ag 2. HCl + NaOH HOH + NaCl 4. Pb(NO 3 ) 2 + 2NaI 2NaNO 3 + PbI 2 2.) In a redox reaction, there is conservation of 1. mass, only 2. charge, only 3. both mass and charge 4. neither mass nor charge Balance each reaction. Classify each reaction. Then decide if it is a REDOX reaction or not. Classification Redox? 3.) _2 Al + 3_Cu(NO 3 ) 2 _3 Cu + 2_Al(NO 3 ) 3 single replacement YES 4.) BaCl 2 + Na 2 CrO 4 BaCrO 4 + 2_NaCl double replacement NO 5.) H 3 PO 4 + _3 KOH _3_H 2 O + K 3 PO 4 neutralization (double replacement) NO 6.) CaCO 3 CaO + CO 2 decomposition NO 7.) N 2 + _3 H 2 _2 NH 3 synthesis YES 8.) CH 4 + O 2 CO 2 + H 2 O combustion YES 9.) A redox reaction is a reaction in which 1. only reduction occurs 3. reduction and oxidation occur at the same time 2. only oxidation occurs 4. reduction occurs first and then oxidation occurs 10.) Oxidation-reduction reactions occur because of the competition between particles for 1. neutrons 2. electrons 3. protons 4. ions

3 SCORE YOURSELF ON THIS DRILL: /10 IF you missed more than 1 or 2, you should do Assignment #1B to get more practice on SKILL #2!! Assignment #1: Redox Reaction Skill Drills (cont d) Skill #3 Identifying Species Oxidized & Reduced (Text Reference: p ) The element which is oxidized gains in oxidation number (becomes more positive) The element which is reduced loses in oxidation number (becomes less positive). Reduction ( G.E.R. ) Oxidation ( L.E.O. ) 1.) Which change occurs when a Sn 2+ ion is oxidized to Sn 4+? 1. two electrons are lost 2. two electrons are gained 3. two protons are lost 4. two protons are gained 2.) When a substance is oxidized, it 1. loses protons. 2. gains protons. 3. loses electrons. 4. gains electrons. 3.) Given the reaction: Fe(s) + Sn 4+ (aq) Fe 2+ (aq) + Sn 2+ (aq) The substance reduced is: 1. Fe(s) 2. Sn 4+ (aq) 3. Fe 2+ (aq) 4. Sn 2+ (aq) 4.) Given the reaction: 2Na(s) + 2H 2 O(l) 2NaOH(aq) + H 2 (g ) Which substance undergoes oxidation? 1. Na 2. NaOH 3. H 2 4. H 2 O 5.) In the reaction: Cu + 2Ag + Cu Ag The Cu atoms are oxidized when they lose 2 electrons. (oxidized or reduced?) (gain or lose?) (how many?) 6.) In any redox reaction, the substance that undergoes reduction will gain (lose or gain?) electrons and as a result the value of the oxidation number will decrease (increase or decrease?). 7.) Given the reaction: Zn(s) + 2 HCl(aq) ZnCl 2 (aq) + H 2 (g) Which statement correctly describes what occurs when this reaction takes place in a closed system? 1. Atoms of Zn(s) lose electrons and are oxidized. 3. There is a loss of mass. 2. Atoms of Zn(s) gain electrons and are reduced. 4. There is a gain of mass. 8.) Given the equation: C(s) + H 2 O(g ) CO(g) + H 2 (g) Which species undergoes reduction? 1. C(s) 2. H + 3. C H 2 (g) 9.) Given the reaction: Zn(s) + Cu 2+ (aq) Zn 2+ (aq) + Cu(s) Which particles must be transferred from one reactant to the other reactant? 1. ions 2. neutrons 3. protons 4. electrons

4 10.) Given the redox reaction: 2I - (aq) + Br 2 (l) 2Br - (aq) + I 2 (s) What occurs during this reaction? 1. The I - ion is oxidized, and its oxidation number increases. 2. The I - ion is oxidized, and its oxidation number decreases. 3. The I - ion is reduced, and its oxidation number increases. 4. The I - ion is reduced, and its oxidation number decreases. SCORE YOURSELF ON THIS DRILL: /10 IF you missed more than 1 or 2, you should do Assignment #1C to get more practice on SKILL #3!! ASSIGNMENT #1A KEY More Skill #1 Assigning Oxidation Numbers Chlorine has several possible oxidation states (-1, 0, +1, +3, +5, +7). Assign the proper state to Cl in each situation below: 1. Cl 2 Cl = 0 2. FeCl 2 Cl = -1 Fe = FeCl 3 Cl = -1 Fe = NaClO Cl = +1 Na = +1 O = NaClO 2 Cl = +3 Na = +1 O = NaClO 3 Cl = +5 Na = +1 O = NaClO 4 Cl = +7 Na = +1 O = -2 Nitrogen is the most complex element there is, having nine possible oxidation states: -3, -2, -1, 0, +1, +2, +3, +4 and +5. Assign oxidation states to each type of atom in each substance. 8. NH 3 N = -3 H = +1 (HINT: ammonia is a rule breaker usually the first element written is the one with the positive oxidation state, but here it is H that is +1, so you work out what N has to be ) 9. N 2 N = NaNO 3 N = +5 Na = +1 O = Al 2 N 3 N = -2 Al = Ca(NO 2 ) 2 N = +3 Ca = +2 O = -2

5 ASSIGNMENT #1B KEY More Skill #2 Identifying Redox Reactions Practice: Figure out which ones of these reactions could be classified as redox reactions. a. 2Na + Cl 2 2 NaCl REDOX b. 2 HNO 3 + 6HI 2 NO + 3 I H 2 O REDOX c. NaOH + HBr NaBr + HOH NOOOOOOO!!!!!! d. 3 H 2 S + 2 HNO 3 3 S + 2NO + 4H 2 O REDOX e. Fe 2 O 3 + 3CO 2Fe + 3CO 2 REDOX f. P + HNO 3 + H2O NO + H 3 PO 4 REDOX g. Ba(NO 3 ) NaOH 2 NaNO 3 + Ba(OH) 2 NOOOOOOO!!!!!! h. 2Al + 3CuCl 2 3Cu + 2AlCl 3 REDOX i. C 2 H 4 + 3O 2 2CO 2 + 2H 2 O REDOX

6 ASSIGNMENT #1C KEY More Skill #3 Identifying Species Oxidized & Reduced PRACTICE: For each reaction on Assign. #1B that IS a redox reaction, identify: The element reduced during the reaction The element oxidized during the reaction a. 2Na 0 + Cl Na 1+ Cl 1- REDOX Cl - reduced Na - oxidized b. 2 H 1+ N 5+ O H 1+ I 1-2 N 2+ O I H 2 1+ O 2- REDOX N - reduced I - oxidized d. 3 H 2 1+ S H 1+ N 5+ O S 0 + 2N 2+ O H 2 1+ O 2- REDOX N - reduced S - oxidized e. Fe 2 3+ O C 2+ O 2-2Fe 0 + 3C 4+ O 2 2- REDOX Fe - reduced C - oxidized f. P 0 + H 1+ N 5+ O 3 2- N - reduced P - oxidized h. 2Al 0 + 3Cu 2+ Cl 2 1- Cu - reduced Al - oxidized + H 2 1+ O 2- N 2+ O 2- + H 3 1+ P 5+ O 4 2-3Cu 0 + 2Al 3+ Cl 3 1- REDOX REDOX i. C 2 2+ H O C 4+ O H 2 1+ O 2- REDOX O - reduced C & H - oxidized

7 ASSIGNMENT #2 KEY Writing Half Reactions Identify the following half reactions as oxidation or reduction. THEN, complete the reaction showing electrons in the right place. 1. Li Li+ + 1 e Fe 2+ Fe e -1 oxidation oxidation 2. P + 3 e -1 P3-6. Mn 4+ Mn e -1 reduction oxidation 3. Ca e -1 Ca 7. Fe e -1 Fe reduction reduction 4. 2 Br 1- Br e H 2 2H e -1 oxidation oxidation

8 Assignment #3 KEY: Balancing Net Ionic Equations Part 1: Balance the half reactions in each pairing Identify which is the oxidation half reaction and which is the reduction half reaction. Combine the half reaction pairs in order to write a balanced skeleton reaction. Explain or show how: # of electrons lost = # of electrons gained 1. Fe +3 + _1 e -1 Fe +2 and Zn Zn +2 + _2 e -1 reduction oxidation 2(Fe e - Fe +2 ) 2 Fe e - 2 Fe +2 ) 2 Fe +3 + Zn 2 Fe +2 + Zn +2 Each Fe +3 ion gains 1 electron (for a total of 2 electrons gained) and each Zn 0 atom loses 2 electrons (for a total of 2 electrons lost). 2. Ca Ca +2 + _2 e -1 and Al e -1 Al oxidation reduction 3(Ca Ca e - ) 2(Al e - Al) 3 Ca 3 Ca e - 2 Al e - 2 Al 3 Ca + 2 Al +3 3 Ca Al Each Ca loses 2e- and each Al gains 3e- (6 electrons lost = 6 electrons gained)! 3. Sr +2 + _2 e -1 Sr and Rb Rb +1 + _1 e -1 reduction oxidation 2(Rb Rb e - ) 2 Rb 2 Rb e Sr Rb Sr + 2 Rb +1 Each Rb loses 1e- and Sr gains 2e- (2 electrons lost = 2 electrons gained)!

9 Assignment #3 KEY: Balancing Net Ionic Equations (Cont d) Part 2: Write balanced half reactions for each of the following unbalanced equations. Indicate which half reaction is oxidation and which is reduction. Combine the half reaction pairs in order to write a balanced net ionic equation Fe 2 O 3 (s) + Mg (s) MgO + FeO Fe e - Fe +2 reduction 2(Fe e - Fe +2 ) 2 Fe e - 2 Fe +2 Mg Mg e - oxidation 2 Fe Mg 1 Mg Fe Ba + 2 Al +3 3 Ba Al Ba Ba e - oxidation 3(Ba Ba e - ) Al e - Al reduction 2(Al e - Al) 6. 4 Al + 3 Ti +4 4 Al Ti Al Al e - oxidation 4(Al Al e - ) Ti e - Ti reduction 3(Ti e - Ti) HCl (aq) + Zn (s) ZnCl 2 (aq) + H 2 (g) 2 H e - H 2 reduction Zn Zn e - oxidation

10 2 H Zn _1 Zn +2 + _1 H 2 Assignment #4 KEY: Spontaneous Reactions & Reference Table J Directions: 1.) Go to the following website (link on your teacher s webpage): 2.) Click on Activity 1, followed by Activity 3. Activity 3: 1.) Click on iron metal, record your observations (in the table below) when each iron metal strip is placed in the four solutions. (Reaction or No Reaction?) 2.) Repeat this process as you place the remaining metals into each solution, being sure to record your observations for each in the table below. SOLUTIONS Fe(NO 3 ) 2 (aq) Pb(NO 3 ) 2 (aq) Ni(NO 3 ) 2 (aq) Sn(NO 3 ) 2 (aq) Fe (s) no reaction reaction reaction reaction METALS Pb (s) no reaction no reaction no reaction no reaction Ni (s) no reaction reaction no reaction reaction Sn (s) no reaction reaction no reaction no reaction 3.) Click on Molecular Scale Reactions. For each of the metal/solution combinations that resulted in a reaction, answer the following questions: Reaction 1: Fe metal and Pb(NO 3 ) 2 solution a.) What substance was oxidized? Fe How many electrons were lost? 2 e - What did this substance change into? Fe +2 b.) What substance was reduced? Pb +2 How many electrons were gained? 2 e - What did this substance change into? Pb c.) Write the balanced skeleton equation for this reaction: Fe + Pb +2 Fe +2 + Pb Reaction 2: Fe metal and Ni(NO 3 ) 2 solution a.) What substance was oxidized? Fe How many electrons were lost? 2 e - What did this substance change into? Fe +2 b.) What substance was reduced? Ni +2

11 How many electrons were gained? 2 e - What did this substance change into? Ni c.) Write the balanced skeleton equation for this reaction: Fe + Ni +2 Fe +2 + Ni Assignment #4: Spontaneous Reactions & Reference Table J (cont d) Activity 4: Place each of the metal strips into the hydrochloric acid (HCl (aq)). 1.) List the metals that DO NOT react with the acid: Ag, Cu 2.) List the metals that DO react with the acid: Fe, Mg, Ni, Pb, Sn, Zn 3.) Click on Molecular Scale Reaction and answer the following for ONE of the reactions between the acid and a metal: a.) What substance was oxidized? How many electrons were lost? 2 e - What did this substance change into? Fe +2 Fe b.) What substance was reduced? H + How many electrons were gained? 1 e - each What did this substance change into? H 2 c.) Write the balanced skeleton equation for this reaction: Fe + 2H + H 2 + Fe +2 Take out Reference Table J: Each of the reactions you observed in this simulation were spontaneous they did not require an additional energy source to make the reaction happen on its own. The placement on Table J is important elements that want to oxidize must be in a certain position relative to the elements that want to reduce. 1.) Look closely at one of your reactions from Activity 3. Compare the element oxidized and the element reduced to their location in the metals column of Table J. Where is the element oxidized in the column, compared to the element reduced? The element oxidized is higher on Table J or more reactive than the element reduced. Ex. Iron (Fe) was oxidezed when reacting with Pb +2 because Fe is higher on Table J and therefore more reactive. 2.) Look at the reaction you chose to analyze for Activity 4. Compare the element oxidized and the element reduced to their location in the metals column of Table J. Where is the element oxidized in the column, compared to the element reduced? The element oxidized is higher on Table J or more reactive than the element reduced.

12 Ex. Iron (Fe) is higher on Table J than H 2 and therefore more reactive. Therefore Fe will become oxidized while H + will become reduced. Assignment #5 KEY: Predicting Spontaneous Reactions Unless you are a genius, you should probably take out Table J now! 1. Based on Table J, which of the following metals is most reactive? a) Ag b) Au c) Ca d) Cu 2. Based on Table J, which of the following metals is most likely to lose electrons? a) Ca b) Co c) Cr d) Cu 3. Based on Table J, which of the following metals is most likely to be oxidized? a) Li b) Na c) K d) Cs 4. Based on Table J, circle the reaction below that is going to be spontaneous. Explain why you chose it: Ca is more readily oxidized than Na! a) Ca + 2 Na +1 Ca Na (Ca is higher than Na on Table J) OR b) 2 Na + Ca +2 2 Na +1 + Ca 5. Circle the pairs for which a spontaneous reaction will occur: a.) Al, Cu 2+ c.) Cu, H + e.) Sn, Pb g.) Au, Ag + b.) Mg 2+, Co d.) Ni 2+, Sn 2+ f.) Li, Ca 2+ h.) H +, Sn 6. On the non-metals side of Chart J, explain why it makes sense that F 2 is most reactive and I 2 is least. Explain using the definition of electronegativity, as well as the electronegativity values. F 2 is the most reactive nonmetal because it has the highest electronegativity (F is 4.0), which means that it has the strongest desire to attract electrons. I 2 is the least reactive nonmetal because it has the lowest electronegativity value (2.7).

13 Assignment #5: Predicting Spontaneous Reactions (cont d) 7. Treasure hunters that search for bounty from sunken Spanish ships often find hordes of gold and silver coins or bullion. Neither metal is very active. However, if the wreck is several hundred years old, the silver is often partially corroded, whereas the gold is not. Explain why based on Table J. Ag is higher than Au on Table J which means that silver (Ag) is more readily oxidized (corroded/reactive) than gold (Au). 8. Check out Figure on p Explain why the zinc blocks are more likely to corrode than the iron hull of the ship, based on Table J. Zn is higher on Table J than Fe and therefore Zn is more easily oxidized (likely to react) than Fe. 9. Which half-reaction correctly represents oxidation? 1. Mg + 2e - Mg Mg 2+ Mg + 2e - 2. Mg e - Mg 4. Mg Mg e Which metal can spontaneously react with Cr +3, according to Table J? 1. nickel 2. lead 3. copper 4. aluminum 11. In the redox reaction: Fe(s) + CuSO 4 (aq) FeSO 4 (aq) + Cu(s), the correctly written reduction half-reaction is 1. Cu + 2 e- Cu Cu e- Cu 2. Cu Cu e- 4. Cu 2+ Cu + 2 e- 12. Which half-reaction correctly represents reduction? 1. Fe e - Fe 0 3. Fe 0 + 2e - Fe Fe 2+ + e - Fe Fe 0 + e - Fe Given the reaction: Ca(s) + Cu 2+ (aq) Ca 2+ (aq) + Cu(s)

14 What is the correct reduction half-reaction? 1. Cu 2+ (aq) + 2e - Cu(s) 2. Cu 2+ (aq) Cu(s) + 2e - 3. Cu(s) + 2e - Cu 2+ (aq) 4. Cu(s) Cu 2+ (aq) + 2e - Assignment #6: Cell Diagrams Directions: For each of the given cell diagrams 1 Write the chemical half reactions for each cell 2 Write a balanced redox equation 3 Label the cathode and the anode 4 Show the direction of electron flow in the external circuit

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17 ASSIGNMENT #7 KEY Electrochemical Cells Electrode: a conductor in a circuit that carries electrons from a substance other than a metal Anode: the electrode where oxidation occurs Voltaic Cell: an electrochemical cell used to spontaneously convert chemical energy to electrical energy Oxidation: losing electrons which makes an atom become more positively charged Electrolytic Cell: a type of electrochemical cell used to cause a chemical change by applying electrical energy Cathode: the electrode where reduction occurs Salt Bridge: strong electrolyte used to separate half-cells in a voltaic cell; preventing mixing but allowing passage of ions Reduction: gaining electrons which makes an atom become more negatively charged ½ Reaction: an equation showing either the oxidation or the reduction that takes place in a redox reaction Drawing of Voltaic Cell and Electrolytic Cell:

18 ASSIGNMENT #8 KEY Topic 4 Drill 1.) 4 2.) 4 3.) 4 4.) 4 5.) 2 6.) 1 7.) 1 8.) 3 9.) 2 10.) 1 11.) 3 12.) 4 13.) 4 14.) 3