Chemistry 30 - Chapter 13 - Cells and Batteries PDF

Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Chapter 13 - Cells and Batteries 1 of 25  Miss Bonora & Mr.Brown Chemistry 30...

Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Chapter 13 - Cells and Batteries 1 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Voltaic Cells Since most Redox reactions occur within solution, the electrons need to be able to flow in and out through a conducting pathway consisting of solid conductors called ___________________________, connecting wire, and conducting solution called _______________________________________. Some voltaic cells use a porous membrane to separate the half-cells. But, most connect the half-cells using a ____________________________________________ Anodes and Cathodes Anodes The electrode where _______________________ occurs is called the _____________. If the anode is a metal, it __________________ mass as the cell operates. The anode is labelled as ___________ since it is the electrode where the negative electrons originate and are ___________. ________________ move to the anode. 2 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Cathodes The electrode where _____________________ occurs is called the ________________. If the cathode is a metal, it ____________________ mass as the cell operates. The cathode is labelled as ___________ since the anode is labelled negative and it gains electrons. _______________ move to the cathode. How does this all work? Here’s a sketch to show how particles move in a cell. Building Voltaic Cells In order to construct a basic voltaic cell you must remember your 5 step method to determine materials that would be able to create a SPONTANEOUS redox reaction. Here is a process we can follow that uses the 5 step method: 1. Find all OAs and RAs provided. If none are provided YOU are in control of what to use! 2. Find the SOA and SRA. They can be any part of the cell provided, solutions or solid electrodes. 3. Find the ½ reactions in your data booklet or textbook. 4. Follow our sketching process to put it all together. Remember to place each half reaction in their own half cell. Connect the two half cells with a salt bridge! 3 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Practicing Together Create a voltaic cell using copper and zinc electrodes. Sketch the cell and label all of the relevant components including: cathode, anode, flow of e-, and flow of ions. Questions for Discussion What is the SOA? ___________ What is the SRA? ___________ Which metal electrode is the anode? ___________ Which metal electrode is the cathode? ___________ Your Turn Create a voltaic cell using silver and chromium electrodes. Sketch the cell and label all of the relevant components including: cathode, anode, flow of e-, and flow of ions. Provide the SOA and SRA in the blanks under your sketch. SOA ___________ SRA ___________ 4 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Inert Electrodes Certain solutions can be used as an OA or RA that do not have a solid metal that they can be paired with. In order to use these solutions we must use an _____________________________________________. Very strong oxidizing agents are most likely to require an inert electrode. Here are some examples: There are two common inert electrodes used in the creation of a cell: They are _______________________ and ____________________________ Adding an inert electrode may change how a cell would normally work, especially if a metal electrode could have been used. Now you must read each question carefully and go through our construction process to determine if we need to change the materials of a cell or not. Practicing Together Create a voltaic cell using carbon and silver electrodes. The electrolyte in the half-cell with carbon is copper(II) nitrate. Sketch the cell and label all of the relevant components including: cathode, anode, flow of e-, and flow of ions. 5 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Your Turn Create a voltaic cell using platinum and lead electrodes. The electrolyte in the half-cell with the inert electrode is acidified potassium dichromate. Sketch the cell and label all of the relevant components including: cathode, anode, flow of e-, and flow of ions Cell Notation Cells can be described using a special notation called cell notation. The standard form of the notation is described by the image below. This notation can be reversed, so you need to make sure you predict precisely which side is the anode and which side is the cathode! Single line ________ separates ______________________ (electrode from electrolyte) Double line _______ represents the ___________________ or __________________ and separates the two ________________ A comma separates chemical species in the same __________________________ 6 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Practicing Together Using the image, provide the proper cell notation. Practicing Together Create the net redox equation from the provided cell: Your Turn Create the net redox equation from the provided cell: Practicing Voltaic Cells Pg. 482 #5-7 (5(a) E0 = -0.336 V) 7 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Cell Potentials A __________________cell is a _____________________ cell where each half cell contains all necessary entities at SATP conditions and all aqueous solutions have a concentration of _____________. Standard Cell Potential, _______ cell is the electric potential difference of the cell also known as _____________________. Calculating Cell Potentials Your super table contains values that can be used to calculate cell potential. These values are called _______________________________________, and are represented by the symbol ___________. By analyzing each half cell we can find E0 of the cell. The formula for this is: ______________________________________________________________________________ The higher the E0r the stronger the OA. The lower the E0r the stronger the RA. If the E0 cell is ____________, the reaction occurring is ___________________________. If the E0 cell is ____________, the reaction occurring is ____________________________. Practicing Together Calculate the standard potential for the cells provided. 8 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School An electrochemical cell made of a cadmium electrode in a 1.0 mol/L cadmium nitrate solution and chromium electrode in a 1.0 mol/L chromium(II) nitrate solution? A standard scandium-copper cell is constructed and the cell potential is measured. The voltmeter indicates that the copper electrode is positive. The cell has a potential of 2.454 V. Calculate the potential of the scandium half cell. Your Turn A standard lead-dichromate cell is constructed. Write the cell notation and calculate the standard cell potential. Practicing Cell Potentials Pg. 487 #1-4 9 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Applying Cell References All standard reduction potentials are based on the standard hydrogen half cell being __________ V. This means that all standard reduction potentials that are positive are _________________ OA’s than hydrogen ions and all standard reduction potentials that are negative are ________________. What happens when the reference reaction is changed? __________________________ Practicing Together Adjust the reduction potentials listed to use aluminum as the new cell reference. Using the adjusted potentials calculate the cell potential for the following: 10 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Applications of Voltaic Cells A typical dry cell contains a zinc anode and an inert graphite cathode. The electrolyte is a moist paste of __________________________________________________ The two half reactions for the dry cell are: Anode: ______________________________________________________________________ Cathode: _____________________________________________________________________ Net: _________________________________________________________________________ Here is a sketch of the dry cell: 11 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School The alkaline battery replaced the dry cell as they tend to last longer. The ammonium chloride and zinc chloride are replaced by strongly alkaline potassium hydroxide. The two half reactions for the alkaline cell are: ______________________________________________________________________________ ______________________________________________________________________________ Silver or mercury button batteries are smaller, but just as powerful as dry or alkaline cells. The two half reactions for the button battery are: ______________________________________________________________________________ ______________________________________________________________________________ Secondary cells, rechargeable batteries, are common in many things these days. Two very common secondary cells include the lead-acid battery, and the lithium ion battery. The two half reactions for the lead-acid battery are: ______________________________________________________________________________ ______________________________________________________________________________ Calculate the cell potential ________________________. 12 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Fuel Cells One of the most important cells is the PEM (proton exchange membrane) or Hydrogen Oxygen Fuel Cell. Analyze the following image and create half reactions for the anode and cathode. Other fuel cells are being researched to create something that uses a fuel that can generate hydrogen gas, rather than using other non-environmentally friendly ways to produce hydrogen gas for use in the fuel cell. This cell is called _____________________________________________________________ This cell uses methanol as its fuel source to produce the hydrogen necessary to run the cell. 13 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Corrosion: Unwanted Voltaic Cells Rusting is an example of ______________________________, which is a _______________________________________ redox reaction of materials with substances in their environment. Interesting facts: Not all metals corrode to the same extent as iron. In fact, many metals corrode in air to form a surface coating of metal oxide that, in many cases, adheres to the metal surface and forms a protective layer that prevents the metal from further corrosion. For example, aluminium, chromium, and magnesium are readily oxidized in air to form their oxides, Al2O3, Cr2O3, and MgO. Unless the oxide layer is broken by a cut or a scratch, the layer prevents further corrosion. In contrast, rust easily flakes off from the surface of an iron object and provides little protection against further corrosion. 14 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Corrosion Prevention Simple methods to prevent corrosion include __________________ or __________________ the object to protect the underlying metal from corrosion. But, we can use our knowledge of voltaic cells to create solutions for corrosion prevention. Galvanizing Galvanizing is the process where iron is covered with a protective layer of zinc. The typical half reactions now change to: Forcing the iron to become the ____________________, allows the iron to remain while the zinc becomes the ____________________________________________________. Cathodic Protection Another method to control corrosion is to use the concept of a sacrificial anode, but instead of coating the surface of the object with a ___________________________________ we attach a _______________________________ to the object. Ships and oil pipelines use this method to ensure structural integrity. 15 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Electrolytic Cells Questions for Thought and Analysis Would it be possible to introduce electrical energy from an external source and cause redox reactions to proceed in the opposite direction? If so, what could you accomplish by reversing the direction of redox reactions? A cell that uses an external source of electrical energy to drive a __________________ redox reaction is called an _______________________________________________. You could describe an electrolytic cell as a cell that converts ________________ energy into __________________ energy. The process that takes place in an electrolytic cell is called ___________________________. Constructing Electrolytic Cells Using your textbook as a guide, sketch a generic electrolytic cell in the space provided. What do you notice is different from a voltaic cell? 16 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Voltaic vs. Electrolytic Zinc-Copper Voltaic Cell Zinc-Copper Electrolytic Cell Complete the following table using the chart from pg. 503 in your textbook. This table is EXTREMELY IMPORTANT! Voltaic Cell Electrolytic Cell 17 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Calculate the standard cell potential for the zinc-copper cell. What would the potential be for the reverse reaction? As we discussed before, any negative cell potential denotes a _______________________________________ redox reaction. This value is the ___________________________________________________________ that you would have to apply to drive the cell reaction for an electrolytic cell. Practicing Together What are the cell reactions and the cell potential of the aqueous potassium iodide electrolytic cell? Litmus paper does not change colour in the initial solution and turns blue only near the electrode from which gas bubbles. Why? At the other electrode, a yellow-brown colour and a dark precipitate forms. The yellow brown substance produces a purplish-red colour in the halogen test. Why? 18 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School An electrolytic cell containing cobalt(II) chloride solution and lead electrodes is assembled. a) Predict the reactions at the cathode and anode, and in the overall cell. b) Draw and label a cell diagram for this electrolytic cell, including the power supply. c) What minimum voltage must be applied to make this cell work? Your Turn 19 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School 2. An electrolytic cell is set up with a power supply connected to two nickel electrodes immersed in an aqueous solution containing cadmium nitrate and zinc nitrate. Predict the equations for the initial reaction at each electrode and the net cell reaction. Draw the chemical cell, and calculate the minimum voltage that must be applied to make the reaction occur. The Chloride Anomaly In the electrolysis of an aqueous sodium chloride solution an anomaly was found to occur in which the half reactions would not be as you would expect if carbon electrodes are used. Using our process for predicting the products of a redox reaction, construct the two half reactions, including reduction potentials, that should be used to create the cell. Red: Ox: Net: This is why you must pay very close attention to water as an OA and RA! HOWEVER… 20 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School The reactions that actually occur are as follows: Red: Ox: Net: Why? Water is not at standard conditions and the actual potential for the half reaction is difficult to measure. Water requires approximately 0.6 V of ________________________ to function in the electrolysis of aqueous solutions. Na+ is still too low on the table to overtake water as the SOA, but water becomes a much weaker RA, so much so that Cl becomes the SRA. - THE ANOMALY STATES: IN THE ELECTROLYSIS OF AQUEOUS SOLUTIONS WHERE WATER AND CHLORINE ARE THE ONLY REDUCING AGENTS PRESENT, THE CHLORINE WILL BECOME THE STRONGEST REDUCING AGENT. The Chlor-Alkali Process The production of sodium hydroxide and hydrogen gas from sodium chloride has important industrial applications. Examine the image below to apply your understanding of the chloride anomaly. 21 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Molten Salt Electrolysis - Ending the Anomaly To ensure the production of sodium and chlorine gas in the electrolysis of sodium chloride scientists, specifically Sir Humphry Davy, discovered that you can melt the salt to ensure there is no water present, but still complete the electrolysis. Red: Ox: Practicing Together An electrolysis experiment was carried out with molten sodium chloride, NaCl(l). Determine the half reactions and the minimum voltage required to operate the cell. Your Turn Another experiment is carried out with KCl(l). Determine the half reactions and the minimum voltage required to operate the cell. Practicing Electrolytic Cells Pg. 508 #5-8 Pg. 510 #17-18 22 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Stoichiometry and Faraday’s Law Question for Thought and Analysis How can you quantitatively relate current flowing through a circuit to the reactions occurring in the half-cells? Crash Course Electrical Current (I) is measured in amperes (A). Charge is measured in coulombs (C), and time (t) is measured in seconds (s). This means Amperes = Coulombs / Second or A = C/s Using all of this information Michael Faraday determined that one of electrons has a charge of 9.65 x 10 C. We call this value _______________________________________ 4 To remember the value rewrite it with appropriate units __________________________ Stoichiometry in Electrochemistry Faraday’s Law states: (pg. 516) We can use Faraday’s Law and Faraday’s Constant to find the mass of a product, amount of current used, or time required to produce a specific amount of product. There are two practical applications of this: 1. ______________________________________________ 2. ______________________________________________ We will examine the use of Faraday’s Law and Constant as it applies to electroplating! 23 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Using GMRU We can use our stoichiometric process to determine the theoretical output of a system. This can really help if you are constructing a lab and need to know how much stuff you need, or if it will even work! Practicing Together How long in minutes, will it take a current of 3.50 A to transfer 0.100 mol of electrons? Silver is deposited on objects in a silver electroplating cell. If 0.175 g of silver is to be deposited from a silver cyanide solution in a time of 10.0 min, predict the current required. 24 of 25  Miss Bonora & Mr.Brown Chemistry 30 Brooks Composite High School Your Turn What is the mass of copper deposited at the cathode of a copper electrorefining cell operated at 12.0 A for 40.0 min? Practicing Faraday’s Law Pg. 516 # 9-12 Faraday Challenge Question Pg 520 #5 25 of 25