Electrochemistry Questions and Answers

A student plots the graph of absorbance vs concentration for their sample They end up with a line with the equation y 0 015x 0 006 If the student finds the absorbance of the caffeine solution is 0 117 what would be the concentration of caffeine in mg ml 0 0077

Ni s Ni2 aq Ag aq AB s Which of the following descriptions of the cell is correct Electrons are released at the O Ni electrode and are gained by the Ni2 ions in the anode electrolyte causing Ag to plate on the anode Ag electrode and are gained by the Ag ions in the anode electrolyte causing Ni to plate on the anode Ag electrode and are gained by the Ni ions in the cathode electrolyte causing Ni to plate on the cathode O Ni electrode and are gained by the Ag ions in the cathode electrolyte causing Ag to plate on the cathode

In a galvanic cell ions are able to flow from one half cell to another to prevent charge build up via a a salt bridge Ob the electrodes Oc a voltmetre d a battery

xplain what makes a solution an electrolyte

Electrochemistry is important in many aspects of daily life i Define voltaic cell ii Fill in the blanks for the drawing of a voltaic cell that s made with copper copper II nitrate E 0 34 V and zinc zinc II nitrate E 0 76 V Briefly explain the role of the salt bridge iii Using the equation Esel Ecathede Eanode calculate the overall cell potential for the cell in step b Be sure to show all steps completed to arrive at the answer

A base of the information in this table ect from the following reactions the one s that are spontaneous if any and Ill are spontaneous one is spontaneous hey are all spontaneous and III are spontaneous and II are spontaneous Pregunta 31 Sin responder a n Puntua como 1 00 F Marcar pregunta A base de la informaci n de esta tabla E V Sn aq 2 e Sn ac 0 15 BrOy ac 6 H ac 6 e Br ac 3 H O 1 44 Fe ac 2 e Fe s 0 44 Fe ac e Fe ac 0 771 NO ac 4 H ac 3 e NO g 2 H O 0 96 Seleccione de entre las siguientes reacciones la s que sea n espont neas si alguna 1 BrO3 ac 2NO g H O Br ac 2 NO3 ac 2H ac 11 So fad 50 6d Sn a Fe s

HBr aq LiOH aq a Predict the products b Determine the states s 1 g aq c Write the complete ionic equation d Cross out spectator ions e Write the net ionic equation

Use the images to answer the following question Beaker A 100 Dissociation Beaker B 50 Dissociation How do Beaker A and Beaker B compare O A Beaker A is a strong acid because it is a better conductor of electricity and has more hydronium ions present in solution Be is a weak acid because it is not a good conductor of electricity OB Beaker A is a weak acid because it is not a good conductor of electricity Beaker B is a strong acid because it is a better con of electricity and has more hydronium ions present in solution OC Beakers A and B are both strong acids because both are good conductors of electricity because both have equal numbers of hydronium ions present in solution OD Beakers A and B are both weak acids because neither is a good conductor of electricity because neither have hydronium ions present in solution

High Potential Energy Low Potential Energy Exert Pressure Do not exert pressure Take the shape of their container Take up a portion of the shape of their container Take on no shape of their container

1 Write the short form for the following voltaic cells and calculate the electric potential A Beaker 1 Fe s Fe NO3 2 aq Beaker 2 Cu s Cu NO3 2 aq

3 Al NO3 3 KI NR 4 AgNO3 Na PO4 Ag PO 5 fb NO3 2 Na3PO4 6 Al NO3 3 Na3PO4 1

3 Calculate the electric potential for each voltaic cell and write the reactions at the anode and cathode A Cu 1 1

4 3 2 We Acid base titration is used quite frequently in research labs to titrate buffers or cell culture media to a desired pH This is accomplished by adding acids such as HCI or bases such as NaOH to shift the pH of the solution either to be more acidic or more basic respectively The changes in pH achieved by the addition of the acid or base can be monitored in two ways First the pH shifts can be monitored chemically by adding an acid base indicator such as phenol red Phenol red is a chemical which is normally red at around pH 7 but turns yellow at the lower pH of acidic environments This is a quick way to check the health of cells normally grown at around pH 7 in culture as cellular waste products or contamination will turn the cell culture media yellow The second way to monitor pH is by measuring the conductivity or ability of solution to conduct electricity A student conducted the following titration experiment at room temperature 25 C The solutions used were 0 1 M NaOH 0 1 M NH nd 0 2 M HCI The acid base indicator used was enol red which is purple at pH above 8 2 yellow pH 6 8 and below and red between 8 2 and 6 8 Deriment 1 First several drops of phenol red were added 30 mL of NaOH solution in an Erlenmeyer flask solution was then titrated with HCI while the uctivity was monitored When adding a strong to a solution it is important to add the acid because the heat of hydration for H ions is migh The conductivity of the titrated solution monitored continuously Figure 1 shows the ctivity titration curve conductivity umho cm conductivity umho cm 8642086420 18 16 14 12 10 0 18 16 14 12 10 8 6 4 Lat 2 0 0 Experiment 2 The first experiment was repeated with a weak base NH instead of the NaOH solution while every other condition remained the same Figure 2 shows this conductivity titration curve purple 10 10 purple red 20 30 volume of HCI mL Figure 1 red yellow 20 30 volume of HCI mL Figure 2 40 yellow 40 50 50 1 Lesson 4 Support of Hypotheses Part 2 4 3 2 Weakening the Hypothesis Another student claimed that the pH of the NH solution required a greater volume of HCI to become acidic than the NaOH solution Comparing Figures 1 and 2 is this claim accurate A Yes because the yellow portion of the graphs start at different volumes of HCI B Yes because the conductivity is different in both experiments after 30 mL No because the yellow portion of the graphs both start at the same point near C 30 mL D No because the conductivity is the same in both experiments after 30 mL 2 Is the hypothesis that conductivity always increases as the concentration of acid increases supported by the results of Experiment 1 Yes because the experiment showed that the heat of hydration for H ions increased over time along with the conductivity of the solution G Yes because the slope of the graph is positive as volume of HCI increases over time H No because the conductivity of the solution initially decreased with the addition of acid J No because the conductivity of the solution increased and decreased independently from the concentration of acid in the solution F 3 Suppose a scientist comes up with a theory that the conductivity of a solution is highest before any acid is added to it Which of the experiments results would most strongly contradict this theory JEFTENE A Experiment 1 B Experiment 2 C Both Experiment 1 and Experiment 2 Neither Experiment 1 nor Experiment 2 D Science Tip 50 50 Lifeline You can use the process of elimination to narrow down the answer choices to two gettin rid of two answer choices with the wrong yes no or two answer choices with the wrong supporting deta

Predict the voltage for the cell Cd Cd 1 M Ni 1 M Ni Cd2 aq 2e Cd s E 0 402 V Ni2 aq 2e Ni s E 0 236 V A 0 638 V C 0 166 V B 0 166 V D 0 638 V

Which of the following are weak electrolytes partially dissociate weak acids and bases HNO3 HC2H302 NH3 KCIO3 A HNO3 KCIO3 B HNO3 HC2H302 NH3 KCLO3 C HC2H302 KCIO3 D HNO3 HC2H302 KCIO3 E HC2H3O2 NH3

Which of the following are strong electrolytes Completely dissociate in solution strong aci bases and soluble ionic compounds A HNO3 NH3 KCIO3 B HNO3 KCIO3 C HNO3 HC2H302 NH3 KCLO3 D HNO3 HC2H302 KCIO3 E HC2H302 KCIO3

Consider the cell below Pb 1M Pb NO3 2 As the cell operates V 1M NaNO3 1M Mn NO3 2 Select one a Pb and Mn increases O b Pb and Mn2 decreases O c Pb2 increases as Mn decreases d Pb 1 decreases as Mn 1 increases Mn

Zn a Mg s Products Zn sa Mg Zn s 0 635500 g Mass of solids 0 635500 g 0 980700 g 0 1 M Molarity of metal ag 0M I Clear Liquid Observations Clear

Experiment 3 Does Magnesium reduce Zinc Reactants 1 g Mg s 150 mL Zn aq

points Which of the following corresponds to an ox dation process 1 Fe R e Che CI 3 C r Gu 2e 4 Co 3e 3e Co

009 10 0 points Select the true statement for the following reaction N 3H 2NH 1 Each N atom is oxidized from 1 to 3 Each II atom is reduced from 1 to 0 2 Each N atom is reduced from 0 to 3 Each II atom is oxidized from 0 to 1 3 Each N atom is oxidized from 0 to 3 Each II atom is reduced from 0 to 1 4 Each N atom is reduced from 0 to 6 Each II atom is oxidized from 0 to 2 5 Each N atom is oxidized from 0 to 6 Each II atom is reduced from 0 to 2 6 Each N atom is oxidized from 0 to 3 Each Hatom is reduced from 0 to 1 7 Each N atom is reduced from 1 to 3 Each II atom is oxidized from 1 to 8 Each N atom is reduced from 0 to 3

Consider the following reaction and its AG at 25 00 C Mg s Ni aq Mg aq Ni s AG 408 0 kJ mol Calculate the standard cell potential Ecell for the reaction cell Calculate the equilibrium constant K for the reaction K

A current of 3 96 A is passed through a Ni NO3 2 solution for 1 50 h How much nickel is plated out of the solution mass of nickel

The equilibrium constant kc was found to be 1 8 10 at 25 3 C for 24 Your 1 the reaction 2X s u aq 2X aq Cu s the reduction the substance X Using the following reduction potential for copper what is potential in V for the other half reaction involving Cu aq 2e Culs E 0 30V 2

What would the potential of a standard hydrogen electrode S H E be under the following conditions H 0 20 M PH 4 5 atm T 298 K

In the redox reaction 2KCIO32KCI 302 which element is oxidized and which is reduced K is oxidized and Cl is reduced O Cl is oxidized and O is reduced OK is oxidized and O is reduced OCl is reduced and O is oxidized O Cl is oxidized and K is reduced

The reaction between finely powdered iron and oxygen results in the formation of iron III oxide and heat 4Fe s 30 g 2Fe O3 s AHO rxn 822 kJ mol Which is the best qualification for this reaction O An exothermic oxidation reduction reaction O An endothermic oxidation reduction reaction On exothermic precipitation reaction O An endothermic acid base reaction O An exothermic disproportionation reaction

Which of the following reactions is a redox reaction O HNO3 aq KOH aq KNO3 aq H O l O CO32 aq HSO4 aq HCO3 aq SO4 aq O Pb NO3 2 aq 2NH4Cl aq NH4NO3 aq PbCl s O ICI s H O 1 HCl aq HIO aq O Fe O3 s 3CO g 2Fe s 3CO g

MnO4 Mn 04 MnO4 Mn 04 a What is the mechanism for reaction according to the kinetic model of electron transfer Assuming that the separation step happens much faster than the reverse electron transfer and the electron transfer step happens much faster than the complex dissociation step b What is the rate constant for this reaction in terms of kets ka and or ka where ket ka and ka are the forward electron transfer forward complex formation and reverse complex formation rate constants respectively c Under these conditions what is the rate limiting step Justify your answer mathematically

A galvanic cell consists of an Cd s Cd2 aq half cell and a Zn s Zn2 aq half cell connected by a salt bridge Reduction occurs in the cadmium half cell The cell can be represented in standard notation as Cd s Cd2 aq Zn s Zn aq Zn s Zn aq Cd s Cd aq Zn s Zn2 aq Cd aq Cd s Cd2 aq Cd s Zn s Zn aq Zn2 aq Zn s Cd s Cd aq

A galvanic cell consists of an Cu s Cu2 aq half cell and a Cd s Cd aq half cell connected by a salt bridge Oxidation occurs in the cadmium half cell The cell c represented in standard notation as Cu s Cu2 aq Cd s Cd aq Cd s Cd2 aq Cu aq Cu s Cd aq Cd s Cu s Cu aq Cu2 aq Cu s Cd s Cd aq Cd s Cd2 aq Cu s Cu aq

The equilibrium constant Kc was found to be 1 1 x 103 at 26 4 C for the reaction 2X s Cu2 aq 2X aq Cu s Using the following reduction potential for copper what is the reduction potential in V for the other half reaction involving the substance X Cu2 aq 2e Cu s E 0 32 V Do not put units in your answer Report your answer with 2 places after the decimal point Type your answer

O HC H302 aq O H O 1 O HgO aq O C H O aq O two of these Question 34 Calculate the OH in a solution that has a pH of 3 71 O 5 1 x 10 11 M O 1 0 x 10 7 M O 1 9 x 10 4 M Q 2 7 10 15 M 1 pts

A student adds 15 0 g of LiBr s to an insulated container holding 150 0 g of water at 22 0 C After the LiBr s has completely dissolved the final temperature of the solution is 34 2 C Calculate the amount of heat in kJ that was absorbed by the solution during the dissolution process Assume that the solution has a specific heat of 4 18 J g C Write your answer using three significant figures k J

Alkaline batteries are used in automobiles True O False

Corrosion can be defined as the reduction of metals True False

Using the activity list included in this problem which element ion is the most resistant to oxidation Sn s Activity Series Pb s none of the above OH Sn2 aq 2e Pb2 aq 2e H g 2H aq 2e Cu s Cu2 aq 2e Cu 2 O Pb

An electrochemical cell is based on the coupling of a spontaneous redox reaction True O False

It can be shown that copper metal lies below H2 on the activity series of metals This means that copper will dissolve in hydrochloric acid O True False

What always happens to a reducing agent during a redox reaction It is oxidized It is reduced It becomes a liquid It becomes a gas

Electrolysis is the process in which an electrical current is used to force a non spontaneous redox reaction to occur Electrolysis describes a measure of opposition to alternating current AC Electrolysis is the opposition of a circuit element to a change of electric current or voltage due to that element s capacitance or inductance Electrolysis measures electrical element opposition

Which metal is the best reducing agent Mg Fe Pb

Determine whether the reaction is a redox reaction Identify the substance being oxidized and the substance being reduced 2K s Br2 1 2KBr s A B C D O A B Redox reaction with K being oxidized and Br being reduced Redox reaction with K being oxidized and KBr being reduced Redox reaction with KBr being oxidized and Br2 being reduced Not a redox reaction

How can you use the activity series to determine whether a metal will dissolve in acids such as HCI aq or HBr aq A B C D C A B Metals above Fe on the activity series will dissolve in acids while metals below Fe will not dissolve in acids Metals below H on the activity series will dissolve in acids while metals above H will not dissolve in acids Metals above H on the activity series will dissolve in acids while metals below H will not dissolve in acids Metals above Fe on the activity series will dissolve in acids while metals below Fe will not dissolve in acids

What is an oxidation reduction or redox reaction Redox reactions involve the transfer of electrons between reactants Redox reactions involve the loss or the acquisition of electrons by one or more of the reactants

Lead is listed below zinc in the activity series What will most likely happen when zinc particles are placed in lead nitrate solution Zinc lead will form Oxygen will evolve No reaction will occur Zinc nitrate will form

An electrolytic cell is prepared for the purpose of producing chlorine gas Cl2 g from molten magnesium chloride MgCl2 Consider the half reactions listed below During operation chlorine gas will be produced at the Mg2 2e Mg Cl 2e 2CI E 2 356 V vs SHE E 1 358 V vs SHE Select one O a negative terminal O b more than one of these O c salt bridge O d anode O e cathode

A voltaic cell is constructed by wiring a lead electrode bathed in 1 0 M Pb aq to a copper electrode bathed in 1 0 M Cu aq with the two solutions connected by a salt bridge Consider the two half reactions listed below What is the cell voltage for this device E 0 13 V vs SHE E 0 34 V vs SHE Pb aq 2e Pb s Cu aq 2e Cu s Select one O a 0 47 V O b 0 11 V O C 0 21 V O d 0 21 V O e 0 47 V 4

Based on the half reactions below which of the following chemical species is the strongest oxidizing agent EO 0 257 V vs SHE Ni aq 2e Pb aq EO 0 13 V vs SHE Select one 2e Pb s O a Pb2 O b Ni aq aq O c Pb s O d Ni s Ni s

An electrolytic cell is used to produce calcium metal from a bath of molten calcium chloride The relevant cathodic half reaction is as follows Ca 2e Ca How many grams of calcium metal are produced if a constant current of 24 7 amps is passed for 31 minutes and 55 seconds assuming a 100 Faradaic efficiency for calcium production g rt your answer with 3 significant figures