1. Indicate whether the following balanced equations inviove oxidation reduction
ID: 850702 • Letter: 1
Question
1. Indicate whether the following balanced equations inviove oxidation reduction. If they do, identify the elements that undergo changes in oxidation number.
a) PBr3(l) + 3 H2O (l) --> H3PO3(aq) + 3 HBr(aq)
b)NaI(aq) + 3 HOCl(aq) -->NaIO3(aq) + 3 HCl (aq)
c) 3 SO2 (g) + 2 HNO3 (aq) + 2 H2O (l) --> 3 H2SO4(aq) + 2 NO(g)
d) 2 H2SO4 (aq) + 2 NaBr(s) --> Br2 (l) + SO
2. A volatic cell is constructed with two silver silver chloride electrodes, each of which is based on the follwoing half reaction: AgCl(s) + e- --> Ag(s) + Cl- (aq). The two half cells have [Cl-]=0.0150 M and [Cl-]=2.55 M, respectively. a) Which electrode is the cathode of the cell? b) What is the standard emf of the cell? c) What is the cell emf for the concentrations given? d) For each electrode, predict whether [Cl-] will increase, decrease, or stay the same as the cell operates.
3.A voltaic cell is constructed that is bases on the following reaction : Sn2+(aq) + Pb(s) --> Sn(s) + Pb2+(aq). a) If the concentration of Sn2+ in the cathode half cell is 1.00M and the cell generates an emf of +0.22 V, what is the concentration of Pb2+ in the anode half cell? b) If the anode half cell contains [SO42-] = 1.00 M in equilibrium with PbSO4 (s), what is the Ksp of PbSO4?
4. An iron object is plated with a coating of cobalt to protect against corrosion. Does the cobalt protect iron by cathodic protection. Explan?
5. Metallic magnesium can be made by the electrolysis of molten MgCl2. a) What mass of Mg is formd by passing a current of 4.55 A through molten MgCl2, for 4.50 days? b) How many minutes are needed to plate out 25.00 g Mg from molten MgCl2 using 3.50 A of current?
Explanation / Answer
1)Redox (portmanteau of reduction and oxidation) reactions include all chemical reactions in which atoms have their oxidation state changed; in general, redox reactions involve the transfer of electrons between species.
This can be either a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO
2) or the reduction of carbon by hydrogen to yield methane (CH4), or a complex process such as the oxidation of glucose (C6H12O6) in the human body through a series of complex electron transfer processes.
The term "redox" comes from two concepts involved with electron transfer: reduction and oxidation.[1] It can be explained in simple terms:
Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion.
Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.
a)P shows -3 and becomes +3 so there is a loss of electron thus its oxidation
b)In the same manner Na shows +1 yo +5 so oxidation
c)S was +4 and now it is -6 so reduction or gain of electron.N also shows reduction +2->+5
d)S was +6 now it is +2 so Reduction.Br -1->0 so Oxidation
This may help you
Electroplating is a process that uses electrical current to reduce dissolved metal cations so that they form a coherent metal coating on an electrode. The term is also used for electrical oxidation of anions onto a solid substrate, as in the formation silver chloride on silver wire to make silver/silver-chloride electrodes. Electroplating is primarily used to change the surface properties of an object (e.g. abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc.), but may also be used to build up thickness on undersized parts or to form objects by electroforming.
The process used in electroplating is called electrodeposition. It is analogous to a galvanic cell acting in reverse. The part to be plated is the cathode of the circuit. In one technique, the anode is made of the metal to be plated on the part. Both components are immersed in a solution called an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A power supply supplies a direct current to the anode, oxidizing the metal atoms that comprise it and allowing them to dissolve in the solution. At the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the cathode, such that they "plate out" onto the cathode. The rate at which the anode is dissolved is equal to the rate at which the cathode is plated, vis-a-vis the current flowing through the circuit. In this manner, the ions in the electrolyte bath are continuously replenished by the anode
The cations associate with the anions in the solution. These cations are reduced at the cathode to deposit in the metallic, zero valence state. For example, in an acid solution, copper is oxidized at the anode to Cu2+ by losing two electrons. The Cu2+ associates with the anion SO42- in the solution to form copper sulfate. At the cathode, the Cu2+ is reduced to metallic copper by gaining two electrons. The result is the effective transfer of copper from the anode source to a plate covering the cathode.
The plating is most commonly a single metallic element, not an alloy. However, some alloys can be electrodeposited, notably brass and solder.
Many plating baths include cyanides of other metals (e.g., potassium cyanide) in addition to cyanides of the metal to be deposited. These free cyanides facilitate anode corrosion, help to maintain a constant metal ion level and contribute to conductivity. Additionally, non-metal chemicals such as carbonates and phosphates may be added to increase conductivity.
When plating is not desired on certain areas of the substrate, stop-offs are applied to prevent the bath from coming in contact with the substrate. Typical stop-offs include tape, foil, lacquers, and waxes
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