PRINCIPLES CHEMSTRY CHEM 120
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This 5 page Class Notes was uploaded by Carmela Kilback on Wednesday September 9, 2015. The Class Notes belongs to CHEM 120 at University of Washington taught by Staff in Fall. Since its upload, it has received 19 views. For similar materials see /class/192608/chem-120-university-of-washington in Chemistry at University of Washington.
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Date Created: 09/09/15
Question In this equation which elements are oxidized and which are reduced Zns 2HClaq 9 H2g ZnC12aq Answer choices a Zn is oxidized and H is reduced b ZnC12 is oxidized and H is reduced c H is oxidized and Cl is reduced d Cl is oxidized and H is reduced Correct answer is B Explanation solution that shows why it is correct Zns 2HClaq 9 H2g ZnC12aq Zn has no charge 2H and 2Cl H has no charge Zn has 2 charge Net ionic equation Zn 2H 9 H Zn2 Spectator ion Cl ZnC12 is oxidized because Zn loses 2 electrons when it becomes Zn2 with Cl H is reduced because as a reactant it forms a H ion with Cl and as a product it does not have a charge which tells us that it gained electrons For each incorrect answer why is it incorrect what misunderstanding might lead students to choose it as their answer a This is wrong because Zn is not correct it is the complete ZnC12 that is oxidized not just Zn c This is wrong because H is reduced not oxidized and Cl is not an option for reduction or oxidation because it is an cation This is wrong because again Cl is a cation and cannot be oxidized 3 1 Will a reaction take place if aqueous solutions of sodium chloride and lead nitrate are mixed If a reaction will take place what would the products be A Yes PbC12aq 2NaNO3s B No reaction will take place C Yes PbC12s 2NaNO3aq D Yes PbCls NaNO3 aq Solution 2NaClaq PbNO32aq 9 PbC12s 2NaNO3aq Correct answer C A reaction takes place because PbC12 is insoluble This is a precipitation reaction If the student answered A they misinterpreted the solubility rules If the student answered B they misinterpreted the solubility rules or did not understand the type of reaction involved If the student answered D they probably forgot to make sure that the compounds have net charge of zero and balance the reaction An evil witch living in the deep dark forest has a specialty shop wherein she sells poisonous plants She knows that many plants have oxalic acid H3C204 or sodium oxalate Na2C204 A customer another evil stepmotherAAilikely Snow WhiteAA s comes in wishing to buy a plant to strangle her step daughter with The witch knows that the plants containing oxalic acid H3C204 or sodium oxalate Na2C204 have these properties causing swelling in the respiratory tract which cuts off air ow effectively strangling the person who as ingested it It turns out that the oxalate ion C204 AA72 will precipitate out as calcium oxalate which happens to be insoluble in water This is a common way to determine the amount of the oxalate ion that you have The witch needs to know how much C202 AA72 she hasAAialways important when working in sales The witch just happens to have some CaCl2 She lls her cauldron with water and adds the reactants She nds to be the net ionic equation she is after all an evil witch and is only really concerned with the reactants and product actually involved in the reaction a C204 2 aq Ca 2 aq gt CaC204 s b H3C204 aq CaCl2 aq gt CaC204 s H g 2C1 1 aq c Na2C204 aq CaCl2 aq gt CaC204 s NaCl aq d 2Na 1 aq 2C 3 aq 40 2 aq Ca 2 aq 2 C1 1 aq gt CaC204 s 2Na 1 aq 2 C1 1 aq Explanation and Reasoning correct incorrect and why a student might choose them a correct this is the net ionic equation it shows only those components directly involved in the reaction which is the de nition of net ionic equation b incorrect this is not the net ionic equation it is another way of showing the molecular equation showing what actually happens in the reaction A student might choose this answer if they were unsure about the actual de nition of net ionic equation and saw the ions on the product side c incorrect this is not the net ionic equation it is another way of showing the molecular equation A student might choose this answer if they were unsure about the actual de nition of net ionic equation d incorrect this is not the net ionic equation it is the complete ionic equation much more information than the witch actually cares about A student might choose this answer if they had confused net ionic and complete ionic equation Following the combustion reaction please select the correct reaction for complete combustion of CH4 in a balanced molecular equation A CH4g 202g gt C02g 2H201 B CH4g 202g gt COg 2H201 C CH4g 20g gt C02g 2H20g D CH4g 202g gt C02g 2H20g D Is the correct answer as it lists the products and their states A Is incorrect because it is a gas H2O is a gas after combustion B Is incorrect as CO is not a product of complete combustion B Is incorrect as O is diatomic in combustion Demitri and Anistasia are bored and are trying to nd something to do So they wandered into Resputin39s layer As they entered Bartock knocked down two of Resputin39s testtubes containing hydrochloric acid and silver nitrate that were both aqueous Once they react together what are the products Does a precipitate form Answers A AgClaq HNO3aq No precipitate is formed B C12 AgNO3 H2 Precipitate is formed AgNO3 C AgH ClNO3 No precipitate is formed D AgCls HNO3aq Precipitate is formed AgCl Correct Answer D AgCls HNO3aq Precipitate is formed AgCl This is because there is a cation paired up with an anion and from looking at the solubility rules one can determine that AgCl is not a soluble compound Therefore making it a solid Th compound with N03 is soluble because a compound containing N03 is almost always soluble Incorrect Answers A AgClaq HNO3aq No precipitate is formed This is incorrect because AgCl is not an aqueous compound and because of this one found that there is no precipitate when there should be B Cl2 AgNO3 H2 Precipitate is formed AgNO3 This is incorrect because the Precipitate and the products are incorect C AgH ClNO3 No precipitate is formed This is incorrect because the cations are paired together and the anions are paired together