Mathematics Education

Redox reaction, Electrolysis and Electrochemistry group 8 1. Rini Kurniasih K1310069 2. Susi Cahyanti K1310076 3. Wahyu Nugroho K1310082 Mathematics Education Training Teacher and Education Faculty SEBELAS MARET UNIVERSITY (UNS) 2011

2 CONTENTS I. TITLE... 3 II. OBJECTIVES... 3 III. BASIC THEORY... 3 III.1 REDOX REACTION... 3 III.2 ELECTROLYSIS... 5 III.3 ELECTROCHEMISTRY... 5 IV. EQUIPMENTS AND MATERIALS... 8 IV.1 REDOX REACTION... 8 IV.2 ELECTROLYSIS... 9 IV.3 ELECTROCHEMISTRY... 10 V. PROCEDURE... 12 V.1 REDOX REACTION... 12 V.2 ELECTROLYSIS... 12 V.3 ELECTROCHEMISTRY... 12 VI. OBSERVATION DATA... 13 VI.1 REDOX REACTION... 13 VI.2 ELECTROLYSIS... 13 VI.3 ELECTROCHEMISTRY... 13 VII. DATA ANALYZE... 14 VII.1 REDOX REACTION... 14 VII.2 ELECTROLYSIS... 16 VII.3 ELECTROCHEMISTRY... 19 VIII. CONCLUSION... 21 IX. BIBLIOGRAPHY... 22

3 PAPER OF BASIC CHEMISTRY 2 EXPERIMENT I. TITLE Redox Reaction, Electrolysis and Electrochemistry II. OBJECTIVES 1. Knowing the redox reaction 2. Studying about chemistry reaction by elecrtric current 3. Knowing the oxidation reaction and reduction reaction zinc metal with cuprum in solution and measure cell potential III. BASIC THEORY III.1 REDOX REACTIO N Redox (shorthand for REDuction-OXidation) reactions describe all chemical reactions in which atoms have their oxidation number (oxidation state) changed. 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 (CH 4 ), or a complex process such as the oxidation of sugar (C 6 H 12 O 6 ) in the human body through a series of complex electron transfer processes. The term comes from the two concepts of reduction and oxidation. 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. Though sufficient for many purposes, these descriptions are not precisely correct. Oxidation and reduction properly refer to a change in oxidation number the actual transfer of electrons may never occur.

4 Thus, oxidation is better defined as an increase in oxidation number, and reduction as a decrease in oxidation number. In practice, the transfer of electrons will always cause a change in oxidation number, but there are many reactions that are classed as "redox" even though no electron transfer occurs (such as those involving covalent bonds). Non-redox reactions, which do not involve changes in formal charge, are known as metathesis reactions. Reduction potential is used to calculate the standard electrode potential (E o cell). This is the equation most commonly seen in textbooks: where: E o cell is the standard electrode potential (in volts). E o red is standard reduction potential of the reducing agent. E o oxi is negative of the standard reduction potential of the oxidizing agent. though the following equation is generally more useful as one is usually only given reduction potentials, not oxidation potentials : or equivalently: where: E o cell is the standard electrode potential (in volts). E o cathode is standard reduction potential of the reducing agent. E o anode is the standard reduction potential of the oxidizing agent.

5 III.2 ELECTROLYSIS Electrolysis is the passage of a direct electric current through an ionic substance that is either molten or dissolved in a suitable solvent, resulting in chemical reactions at the electrodes and separation of materials. The main components required to achieve electrolysis are : An electrolyte : a substance containing free ions which are the carriers of electric current in the electrolyte. If the ions are not mobile, as in a solid salt then electrolysis cannot occur. A direct current (DC) supply : provides the energy necessary to create or discharge the ions in the electrolyte. Electric current is carried by electrons in the external circuit. Two electrodes : an electrical conductor which provides the physical interface between the electrical circuit providing the energy and the electrolyte Electrodes of metal, graphite and semiconductor material are widely used. Choice of suitable electrode depends on chemical reactivity between the electrode and electrolyte and the cost of manufacture. III.3 ELECTROCHEMISTRY Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor (a metal or a semiconductor) and an ionic conductor (the electrolyte), and which involve electron transfer between the electrode and the electrolyte or species in solution.

6 If a chemical reaction is driven by an external applied voltage, as in electrolysis, or if a voltage is created by a chemical reaction as in a battery, it is an electrochemical reaction. In contrast, chemical reactions where electrons are transferred between molecules are called oxidation/reduction (redox) reactions. In general, electrochemistry deals with situations where oxidation and reduction reactions are separated in space or time, connected by an external electric circuit to understand each process. An electrochemical cell is a device that produces an electric current from energy released by a spontaneous redox reaction. Electrochemical cells have two conductive electrodes (the anode and the cathode). The anode is defined as the electrode where oxidation occurs and the cathode is the electrode where the reduction takes place. Electrodes can be made from any sufficiently conductive materials, such as metals, semiconductors, graphite, and even conductive polymers. In between these electrodes is the electrolyte, which contains ions that can freely move. The Galvanic cell uses two different metal electrodes, each in an electrolyte where the positively charged ions are the oxidized form of the electrode metal. One electrode will undergo oxidation (the anode) and the other will undergo reduction (the cathode). The metal of the anode will oxidize, going from an oxidation state of 0 (in the solid form) to a positive oxidation state and become an ion. At the cathode, the metal ion in solution will accept one or more electrons from the cathode and the ion's oxidation state is reduced to 0. This forms a solid metal that electrodeposits on the cathode. The two electrodes must be electrically connected to each other, allowing for a flow of electrons that leave the metal of the anode and flow through this connection to the ions at the surface of the cathode. This flow of electrons is an electrical current that can be used to do work, such as turn a motor or power a light. A Galvanic cell whose electrodes are zinc and copper submerged in zinc sulfate and copper sulfate, respectively, is known as a Daniell cell. Half reactions for a Daniell cell are these:

7 Zinc electrode (anode): Zn (s) Zn 2+ (aq) + 2 e - Copper electrode (cathode): Cu 2+ (aq)+ 2 e - Cu (s) A modern cell stand for electrochemical research. The electrodes attach to high-quality metallic wires, and the stand is attached to a potentiostat/galvanostat (not pictured). A shot glass-shaped container is aerated with a noble gas and sealed with the Teflon block. In this example, the anode is zinc metal which oxidizes (loses electrons) to form zinc ions in solution, and copper ions accept electrons from the copper metal electrode and the ions deposit at the copper cathode as an electrodeposit. This cell forms a simple battery as it will spontaneously generate a flow of electrical current from the anode to the cathode through the external connection. This reaction can be driven in reverse by applying a voltage, resulting in the deposition of zinc metal at the anode and formation of copper ions at the cathode. To provide a complete electric circuit, there must also be an ionic conduction path between the anode and cathode electrolytes in addition to the electron conduction path. The simplest ionic conduction path is to provide a liquid junction. To avoid mixing between the two electrolytes, the liquid junction can be provided through a porous plug that allows ion flow while reducing electrolyte mixing. To further minimize mixing of the electrolytes, a salt bridge can be used which consists of an electrolyte saturated gel in an inverted U-tube. As the negatively charged electrons flow in one direction around this circuit, the positively charged metal ions flow in the opposite direction in the electrolyte. A voltmeter is capable of measuring the change of electrical potential between the anode and the cathode. Electrochemical cell voltage is also referred to as electromotive force or emf. A cell diagram can be used to trace the path of the electrons in the electrochemical cell. For example, here is a cell diagram of a Daniell cell: Zn (s) Zn 2+ (1M) Cu 2+ (1M) Cu (s)

8 First, the reduced form of the metal to be oxidized at the anode (Zn) is written. This is separated from its oxidized form by a vertical line, which represents the limit between the phases (oxidation changes). The double vertical lines represent the saline bridge on the cell. Finally, the oxidized form of the metal to be reduced at the cathode, is written, separated from its reduced form by the vertical line. The electrolyte concentration is given as it is an important variable in determining the cell potential. IV. EQUIPMENTS AND MATERIALS IV.1 Redox Reaction No. Name Picture 1. Measurement glass 1 Quantity 2. Pippete 2 3. Reaction tube rack 1 4. Reaction tube 6

9 No. Name Quantity 1. Solution CuSO 4 0.5M 4 ml 2. Solution ZnSO 4 0.5M 4 ml 3. Solution FeCl 3 4 ml 4. Metal Cu 2 piece 5. Metal Zn 2 piece 6. Metal Fe 2 piece IV.2 Electrolysis No. Name Picture Quantity 1. Funnel 1 2. Power supply 1 3. Carbon electrode 2

10 4. Pippete 2 5. Measuring glass 1 6. U pipe 1 No. Name Quantity 1. Solution KI 0.5 M sufficient 2. Solution NaCl 0.5 M sufficient 3. Solution of PP 2 drop 4. Solution of amylum 2 drop IV.3 Electrochemistry No. Name Picture Quantity

11 1. Funnel 1 2. Beaker glass 2 3. Multimeter 1 4. Pippete 2 5. Salt bridge 1 No. Name Quantity 1. Solution ZnSO 4 0.5 M sufficient 2. SolutionCuSO 4 0.5 M sufficient

12 3. Salt solution sufficient 4. Metal Zn 1 piece 5. Metal Cu 1 piece V. PROCEDURE V.1 Redox Reaction 1. Enter 2 ml CuSO 4 solution into the reaction tube add Zn metal. Let it for several minutes and note what happen? By same way done to Fe metal. 2. Enter 2 ml ZnSO 4 solution into the reaction tube, then add Cu metal. Let it for several minutes and note what happen by same way, done to Fe metal. 3. Repeat by some way to FeCl 3 solution with Cu and Zn metal. V.2 Electrolysis KI and NaCl solution 1. Enter KI solution 0.5 M into U tube until glue form top and U tube. 2. Connect electrodes with source of electric current during less more 5 minutes. 3. Note the change at anode. 4. Note the change occur at catode with use pipette drop, add 2 drop indicator PP solution at catode space, observe which occur. 5. By use pipette drop, add any drop amylum solution into anode space, observe which occur. 6. Done step 1 to 5 with use NaCl 0.5 M solution. V.3 Electrochemistry Cell 1. Making a half cell. Enter 100 ml ZnSO 4 0.5 M solution into chemistry glass 250 ml. Place a stick of zinc scuff into the glass.

13 2. Making a half cell. Enter 100 ml CuSO 4 0.5 M solution into the chemistry glass 250 ml. Plece a stick of cuprum scuff into the glass. 3. Connect zinc scuff with negative pole of multimeter and connect cuprum scuff with positive pole of voltmeter. 4. Connect both cell with salt bridge. Read voltmeter then note the result. VI. OBSERVATION DATA VI.1 Redox Reaction 1. CuSO 4 +Zn there are bubble 2. CuSO 4 +Fe 3. ZnSO 4 +Cu 4. ZnSO 4 +Fe 5. FeCl 3 +Zn there are bubble and become rusty 6. FeCl 3 +Cu VI.2 Electrolysis 1. KI 0.5 M a. Change on anode (+) : yellow-brown b. After add amylum to anode :black c. Change on cathode (-) : bubbles d. After add PP to cathode : purple 2. NaCl 0.5 M a. Change on anode (+) : light yellow b. After add amylum to anode : light yellow c. Change on cathode (-) : bubbles d. After add PP to cathode : purple VI.3 Electrochemistry toward = 0.6 volt

14 VII. DATA ANALYZE VII.1 Redox Reaction 1. Cu+ZnSO 4 solution cathode : E o red= -0.76 volt anode : E o oxi= -0.34 volt E o cell= -1.1 volt E o cell is negative, therefore reaction can not happen and reactivity Zn>Cu 2. Cu+FeCl 3 solution cathode : E o red= -0.072 volt anode : E o oxi= -0.34 volt E o cell= -0.412 volt E o cell is negative, therefore reaction can not happen and reactivity Fe>Cu 3. Fe+CuSO 4 solution cathode : E o red= 0.34 volt anode : E o oxi= 0.44 volt E o cell= 0.78 volt E o cell is positive, where Cu is oxidator (doing reduction) and Fe is redactor (doing oxidation) and the reactivity Fe>Cu so the reaction is spontan. 4. Fe+ZnSO 4 solution cathode : anode : E o red= -0.76 volt E o oxi= +0.44 volt E o cell= -0.32 volt

15 E o cell is negative, therefore reaction can not happen and reactivity Zn>Fe. 5. Zn+ CuSO 4 solution cathode : E o red= 0.34 volt anode : E o oxi= 0.76 volt E o cell= 1.1 volt E o cell is positive, where Cu is oxidator (doing reduction) and Fe is redactor (doing oxidation) and the reactivity Zn>Cu so the reaction is spontan. 6. Zn+ FeCl 3 solution cathode : E o red= -0.072 volt anode : E o oxi= 0.76 volt E o cell= 0.6888 volt E o cell is positive, where Cu is oxidator (doing reduction) and Fe is redactor (doing oxidation) and the reactivity Zn>Fe so the reaction is spontan. Based on the experiment of redox reaction, the reaction can be occur only CuSO 4 solution add Zn metal and FeCl 3 solution add Zn metal. In the experiment we get the difference which is gotten by calculation. From experiment Zn added in CuSO 4 solution there is changes Zn become brown and there are stratified or powder also there are bubbles. It is match with theory hence occur reaction. While for Fe entered in CuSO 4 there are no changes. It is indicated that not occur reaction. Through the experiment, metal Cu and Fe not react in the ZnSO 4 caused not occurring changes. It is same with metal Cu in the FeCl 3 solution. In the ordered volta metals Li- K-Ba-Ca-Na-Mg-Al-Zn-Fe-Ni-Sn-Pb-H-Cu-Hg-Ag-Pt-Au only can reduct other metal which exist in the right side and can not reduct metal in the left side. Metal which has law reduction potential will have reactivity. According to volta cell set Zn-Fe-Cu. The differences from calculating or theory with the experiment caused by:

16 1. Practicant do not have much time in observing reaction, hence reaction which must occur can not be observed. Practicant can not see bubbles or color changes. 2. Inaccurate when metal Fe, Cu, Zn started to react. 3. The instrument not clean. 4. Metal Fe, Zn, and Cu firstly can not be sandpaper it influence the reaction. Reaction happen spontaneously if potential cell (E o cell) which resulted from the reaction between metal with a solution have positive value. Potential cell is the difference between cathode potential with anode potential. At redox reaction in anode happen oxidation reaction and at cathode happen reduction reaction. Reactivity metals based on calculation in CuSO 4 solution Zn>Fe, in ZnSO 4 solution Fe>Cu and in FeCl 3 solution Zn>Cu. VI.2 Electrolysis Reaction : cathode : anode :

17 In KI solution we get ion K + and I - and water molecule, possibility reaction which occur in the left side is reduction K + ion or reduction of water molecule. Electrolyte solution can conduct electric current. Conduction electric through solution accompanied a reaction which is called electrolysis. Electrolysis is expansion process of electrolyte in the solution form or break by electric current direct. These reaction can take place because the influence of electric current. So, at electrolysis occur changes from electric energy become chemistry energy. If the electric flow through ion compound melt, so the ion compound will be expansion cation reduction in cathode white anion oxidation in anode. If which flowed by electric is electrolyte solution, so reaction which occur not cation and anion, may be water or the electrode. Reaction at cathode: E o = -2.92 volt E o = -0.83 volt Because the reduction potential of water is higher so water able to be reducted hence in cathode form H 2 gasses. Reaction in anode oxidation: E o = -0.54 volt E o = -0.83 volt Because potential I - higher than potential of water oxidation, so at anode form iodine which in this experiment have yellow-brown, so oxidation ion I - will be able to occur. So, at electrolysis KI solution occur reaction with the result H 2 gases, OH -, KI. Reaction is oxidation reaction, we can conclude that in the right side

18 is anode because at anode occur oxidation reaction. While at reaction of conclude at this part look cathode. is reduction reaction and can be Electrolysis KI reaction with C completely: anode : cathode : When flowed by electric current KI solution occur at anode has orange or yellow color rather brown which firstly has clear rather yellow. Based on the experiment result which gotten at anode space which added with amylum solution that occur changes there are change color become brown. While at cathode space which added by PP solution the color change from pure to purple and there exist bubbles. This show that the solution has base properties. The changes at anode if mix with iodine. At anode appear bubbles gass that is H 2 gases. Electrolysis NaCl 0.5 M solution Reaction : anode : cathode : Reaction which occur is below E o = -0.83 volt

19 E o = -2.71 volt At electrolysis of NaCl solution with electrode grafit appear much bubble in the cathode (-), while in the anode (+) the solution change the color. In the cathode there exist bubbles gases caused at this part occur reduction H 2 O reaction. Like which occur at the experiment at anode space which given amylum occur changes become much bubbles gases of Cl 2 and cathode space which added PP appear bubbles H 2 gases just little, not occur change color. From theory we know that in anode from chlorine gases and cathode result hydrogen gases. Ion OH - which occur react with ion Na + hence result NaOH which can be crystaled because the potential reduction of water is higher than Na. Therefore, water more able to reduct hence in cathode form H 2 gases. At this experiment not show that the solution have base properties. The difference between theory and experiment caused by less accurate doing experiment, inaccurate when drop amylum ad PP, the instrument not clean and soon. VI.3 Electrochemistry If an electrolyte solution and metal which act as electrode connected with salt bridge, so will have voltage. Voltage (different putential) E o cell can be calculated by formula.

20 Based on the constanta, the magnitude potential (E o cell) of standart reduction E o = +0.34 volt E o = -0.76 volt The reaction anode : E o oxi= 0.76 volt cathode : E o red= 0.34 volt E o cell= 1.1 volt E o Cu bigger than E o Zn, hence Cu faced reduction and Zn oxidation. At anode occur oxidation reaction that is and cathode occur reduction reaction. Change number (+) which formed in anode equivalent with negative ion which formed in cathode. Negative ions flow from salt bridge to anode, because formed positive ion. Because negative charge formed in cathode, so positive ion flow from salt bridge toward electrode (cathode). Salt bridge function to arrange the equilibrium of ions solution. Metal which faced reduction is metal which faced oxidation is metal which has E o cell smaller or which more difficult to reduct. In ordered volta properties more left, the E o reduction value smaller means more difficult for metal to reduct (more able to oxidated) and more right the E o value bigger means more able to reduct. From the electrochemistry experiment making a half cell by entering 100 ml ZnSO 4 0.5 M into beaker glass also made a half cell entered 100 ml CuSO 4 0.5 M into beaker glass and connected both beaker glass with salt bridge. Positive pole at voltmeter dipped in CuSO 4 solution and negative pole at ZnSO 4 and E o cell at the experiment we obtain 0.6 volt. It is different with the theory, the caused by inaccurate to read voltmeter, instrument not clean and soon.

21 VIII. CONCLUSION 1. Redox is the term used to label reactions in which the acceptance of an electron (reduction) by a material is matched with the donation of an electron (oxidation). Redox reaction happen because there is difference of potential of each element can happen if E o cell positive (E o cell>0). 2. Order of reactivity in the experiment Zn>Fe>Cu. 3. Electrochemistry is the study of solutions of electrolytes and of phenomena occurring at electrodes immersed in these solutions. 4. Cell potential can be calculate with formula Magnitude of cell tension from electrochemistry Zn (s) Zn 2+ Cu 2+ Cu (s) theory : 1.1 volt experiment : 0.6 volt 5. Electrolysis is chemical reaction when lectricity is passed through an liquid solution of an ion or an electrolyte. Electrolysis KI anode : cathode : Electrolysis NaCl anode : cathode :

22 IX. BIBLIOGRAPHY Anshory, irfan.2000.kimia.jakarta:erlangga Brady,james.1994.Kimia Universitas.Jakarta:Erlangga Cliff.D.A et al.chemistry Astructural View Laboratory Manual Edisi3. G.Wulfsberg.2000.Inorganic Chemistry.University Science Book,Sausolito,CA. Keenan,klemfelter/.1986.Kimia Universitas.Jakarta:Erlangga Kuswati,tine maria.2005.sains Kimia.Jakarta:Bumi Aksara http://wikipedia.com(access May16 th 2011) http://google.com(access May16 th 2011) Surakarta, May 17 th 2011 Writer