Electrochemistry Redox Reaction

ELECTROCHEMISTRY Redox Reaction

Electrochemistry is the study deals with interconversion of electrical energy and chemical energy. Chemical reactions involved in electrochemistry are reduction and oxidation that call redox reaction. One type of reaction cannot occur without the other. Electrochemical (redox) is electricity used to drive a non spontaneous chemical reaction (electrolysis). In electrochemistry, redox reaction can be divided into two type of reaction: Reduction: Reduction process gain of electron and oxidation number will decrease. Reduction reaction at cathode. The electrode which is attached to the negative pole of the battery, and which supplies electrons to the electrolyte, is called the cathode. 

Oxidation: oxidation process loss of electron and oxidation number will increase. Oxidation reaction at cathode. The electrode which is attached to the positive pole of battery, and which accepts electrons from the electrolyte, is called anode. 

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ENGAGE

IN ELECTROLYSIS You are given the picture as shown below:

1. What do you observed from the picture given? 2. What is happen when the concentration of ions is increase? 3. What is the function of salt bridge and gives an example of salt bridge. 4. How does the cell maintain its electricity?

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EMPOWER STEPS 1. Electrochemical process is redox reaction, released energy by spontaneous reaction. 2. There are two type of redox reaction: •

Reduction

•

Oxidation

3. Log on the website and observe the animation to answer the question. http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/simDownload/inde x4.html#electrochem RESULT Redox Reaction Before

Electrolysis

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After

Electrolysis 4

Questions 1. What happens at the zinc and copper electrode? 2. Write all the reaction involves and the overall cell reaction. 3. How does the cell maintains its neutrality?

4. What happened if there is no salt bridge?

Answers 1. Zinc electrode: Zinc is more electropositive than copper. Tendency to release

electrons: Zn

(s)

 Zn2+

(aq)

+ 2e-. Zinc dissolves. Oxidation occurs at the zinc

electrode. Zn2+ ions enter ZnSO4 solution. Zinc is the negative electrode since it is a source of electron (anode).

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Copper electrode: The electron from the zinc metal moves out through the wire enter the copper metal. Cu2+ ions from the solution accept electrons. Cu2+

(aq)

+ 2e- Cu

(s)

Copper is deposited. Reduction occurs at the Cu electrode. Cu is the positive electrode (cathode). 2. Reaction involved:

Anode: Zn (s)  Zn2+ (aq) + 2eCathode: Cu2+ (aq) + 2e- Cu (s) _____________________________________________________ Overall cell reaction: Zn (s) + Cu2+ (aq)  Zn2+ (aq) + Cu (s) 3. Left cell: Zn2+ ions enter the solution causing an overall excess of positive charge. Cl-

ions from salt bridge move into zinc half cell. Right cell: Cu2+ ions leave the solution causing an overall excess of negative charge. K+ ions from salt bridge move into Cu half cell. Electrical neutrality is maintained. 4. As the zinc rod dissolves, the concentration of Zn2+ in the left beaker increase. The

reaction stops because the nett increase in positive charge is not neutralized. The excess charge build up can be reduced by adding a salt bridge.

ENHANCE The diagram shows the electrochemical cell of Standard Hydrogen Electrode (SHE).

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Based on the diagram, match the following words with the correct statement. Standard Electrode Potential (Eo)

Standard Hydrogen Electrode (SHE)

Electrode Potential

Electrochemical Cells

Salt bridge

1. ___________ where chemical reaction produces electricity. 2. ___________ is an inverted U tube containing a gel permeated with solution of an inert electrolyte. 3. ___________ is a measure of the ability of a half-cell to attract electrons towards it. 4. ___________ is a measure of the ability of a half-cell to attract electrons towards it at

25oc, the P is 1 atm (for gases), and the concentration of electrolyte is 1M. 5.

___________ is made up of a platinum electrode, immersed in an aqueous

solution of H+ (1 M) and bubbled with hydrogen gas at 1 atm pressure, and temperature at 25 oc.

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