Test ENTHALPY AND ENTROPY OF ZINC WITH COPPER SULFATE The CCLI Initiative Computers in Chemistry Laboratory Instruction LEARNING OBJECTIVES The acquirements objectives of this test are to. . . ! ! individualize diversifys in enthalpy and entropy of the reaction of zinc with copper sulfate using span manners: electrochemistry and calorimetry. collate the enthalpy prizes earned by the span manners. BACKGROUND Thermodynamics is careful with activity diversifys that arise in chemical and substantial mode es. The enthalpy and entropy diversifys of a rule underneathgoing such modees are interakin by the diversify in frank activity, ?
G, according to the equation ?G = ?H – T ? S (1) This search focuses on the reaction Zn(S ) + CuSO4(aq) Y ZnSO4(aq) + Cu(S ) (2) ?G gain be adapted from the ? H and ? S prizes earned electrochemically. The fibre of Equation (1) gain be tested by comparing the prize of ? H earned electrochemically with the prize of ? H earned calorimetrically cessationraint the corresponding reaction. The electrochemical manner The electrochemical manner offers pure and complimentary resources cessationraint the self-indulgence of thermodynamic quantities. A pure electrochemical cell is constrained in a Chem-Carrou-Cell™ platter as shown in Figure 1.
Cu(S )/CuSO4 (aq) || Zn(S )/ZnSO4(aq) (3) Fi? G ure 1: Uplift cessationraint measuring E versus weather. 1 The CCLI Initiative The aggravatetotal galvanic cell reaction is Zn(S ) + Cu2+ (aq) Y Zn2+(aq) + Cu(S ) and it is essentially the corresponding as that preface attribute in the calorimeter. The portion of the electrical activity, F , manufactured or consumed during the electrochemical reaction is a steady estimated per glacis of electrons, and can be complimentaryly estimated. The frank activity diversify, ? G , of an electrochemical reaction is akin to the voltage, E, of the electrochemical cell by the equation (4) G where and = -nFE n (5) F = the compute of glaciss of electrons transferred in a redox reaction. = Faraday’s steady of 96,500 C/glacis of electrons . Combining equations (1) and (5), and dividing twain sides by the steady “n,” we earn a rectirectirectistraight interunarm-an among the voltage diversify, ? E, and the enthalpy and entropy diversifys at contrariant weathers E = – IH + T ? S nF nF I (6) or E = IS (T) – IH nF (7) nF By measuring the voltage E, of our electrochemical cell, at divers weathers, we can earn a frame of the voltage versus weather. Assuming that ? H and ?
S dpolite steady aggravate a paltry weather ramble, we can apportion the ? S and ? H from the appear and the seize of the rectirectistraight sequence respectively appear = IS nF (8) and Y-seize = – IH nF (9) ?G can now be adapted by resources of Equation (1). We can substantiate its prize using Equation (5). Please melody that in twain cases, ? G must be adapted cessationraint the corresponding weather. If the calculations are effected cessationraint 298 K (25 °C), we can also substantiate the testal prize of E° cessationraint this weather by employing the Nernst equation (7) E = E° – RT ln [products ] nF [reactants ] 2 (10)
The CCLI Initiative where E° is the type implicit estimated at 25 ° C and is 1. 100V cessationraint the cell underneathneath remuneration. When the concentrations of the ZnSO4 and CuSO4 resolutions are similar, the log signal of the Nernst equation becomes cipher. Underneathneath these stipulations, the type voltage, E°, of the cell is similar to the estimated voltage, E The calorimetric manner The creative calorimeter is a unmeasuredy insulated vessel which contains a ample unreserved gravity of rerediscerption in infallible irascible contiguity with an complimentary thermometer and a paltry reaction tube (Figure 2).
When estimated quantities of reactants are introduced into the reaction tube, the passion of reaction diversifys the weather of the calorimeter resolution. Figure 2. Diagram of Calorimeter The passion of the chemical reaction is given by the equation IH H n K W Ti Tf = (K + W)(Ti – Tf) n (11) is the passion of reaction at steady constraining. is the compute of glaciss of a limiting reactant as explicit in the redressd equation. is the passion ability of the calorimeter resolution. is the passion ability of the calorimeter. s the judicious weather of the calorimeter resolution. is the definite weather of the calorimeter resolution. The passion ability of the calorimeter rerediscerption is earned by multiplying the specific passion of the rerediscerption (3. 8 J g-1 °C-1 cessationraint CuSO4 ) by the gravity of the rerediscerption in the calorimeter. W, the estimated cup passion ability, is 30 J °C-1 . 3 The CCLI Initiative SAFETY PRECAUTIONS Safety goggles must be barren in the lab at total dates. Any bark contiguityed by chemicals should be washed instantly. BEFORE PERFORMING THIS EXPERIMENT . . . … ou gain need a MicroLAB program preferable of: Part I – measuring voltages and weathers and displaying them in the Graphing , Digital Display and Spreadsheet views. Use delta. G . test supplied by your preceptor. Part II – collecting weather balbutiations as a acquit of date and displaying them in the Graphing, Digital Display and Spreadsheet views. Use passion of Rediscerption from the Date and Weather tab in the MicroLAB hole window. EXPERIMENTAL PROCEDURES Part I: Electrochemistry 1. Calibrate your Weather test at a narrowness of three disjoined weathers with ice-calm instil and fervent tap instil. . Fill a 600 ml beaker three-quarters unmeasured of ice. Fill the cessation of the beaker with calm tap instil until the beaker is filled to individual cm from the summit. Stir the ice/instil conformation to deal-quenched the ice evenly. 3. Attribute the beaker on a fervent platter — don’t deviate the passion on yet! Cessation the Chem-Carrou-CellTM on summit of the beaker so that the bottoms of the polites of the Cell are aggravatewhelmd in the ice/instil conformation. Let the uplift continue cessationraint 15 minutes until the weather stabilizes. 4. Pour environing 5 ml of 0. 1 M KNO3 into the nature polite. Pour environing 5 ml of 0. 0 M ZnSO4 into polite #1 and environing 5 ml of 0. 50 M CuSO4 into polite #2. 5. With uncloggedsedsed tweezers, accept a s skip of percolate pamphlet and decrease individual object into the accessible polite (where immersion in the KNO3 rerediscerption gain trust individual object); decrease the other object into polite #1. Repeat this process with another sskip of percolate pamphlet, decreaseping the other object into polite #2. This creates the salt bridge cessationraint your galvanic cell. 6. With uncloggedsedsed tweezers accept a zinc metal sskip and sand it (on a concern of pamphlet so as referable to dabble the table summit) to dislodge any oxide plaster.
Bobject 2 cm of individual object of the ? S skip and aggravatewhelm it in the ZnSO4 rerediscerption (polite #1). The cessation of the metal sskip (3cm) extends quenched to the edge of the cell and should be predilection aggravate the hem. Repeat the corresponding process with the copper metal sskip and attribute it in polite #2. Later the electrical leads (alligator clips ) from the interface gain be solid to the metal disencumbers. 7. Fasten your weather test to the ring continue with a clamp and enjoin the weather test such that its extremity can be aggravatewhelmd in the accessible polite (KNO3 resolution) of the cell.
It is conjectured that the weather of the ZnSO4 rerediscerption and CuSO4 rerediscerption gain be very arrest to the weather of the KNO3 rerediscerption throughquenched the test. 8. Start the computer program to instructor the weather. 9. Read and archives the weather. Attach the totaligator clips to the metal disencumbers and accept the voltage balbutiation. If a denying compute appears on the protect, inversion the wires. Disbe-mixed the wires instantly succeeding the balbutiation is archivesed. 10. Deviate the fervent platter onto haughty, Start the MicroLAB program, then the program gain rest entire five °C to estimate the voltage and weather.
When the Message window “Attach tests , Cece ENTER to accept a balbutiation, then divorce tests ’’ appears on the protect, be-mixed the voltage leads to the 4 The CCLI Initiative misspobject metal tabs, fabricate positive the voltage is lasting, then cece ENTER, and disbe-mixed the voltage leads until the proximate balbutiation is due. Prolonged be-mixedion of the wires gain origin electric popular to career through the cell. This acquit gain product in diversifys in concentrations of the resolutions. Since the estimated voltage depends on these concentrations, there gain be an fallacy in the voltage balbutiations.
Ssummit the program when the weather reaches 40 °C. Part II: Calorimetry 1. Explore a uncloggedsed, sarcastic 150 ml beaker on the summit loading redress, then supplement 50 ml of 0. 5 M CuSO4 resolution. Explore the beaker a relieve date to individualize the bulk of the rerediscerption in the calorimeter. Nest the 150 ml beaker within a 400 and 600 ml beaker, continuity the memorable rod and weather test through the Styrofoam lid and situation the lid on the vital beaker. The weather test should be as heartfelt into the rerediscerption as feasible notwithstanding withquenched lixiviate. Let the attendance continue ? so that the components win the corresponding weather.
Using the summit loading redress, tare the malleable exploreing boat, then explore 0. 5 grams of zinc interlard into a malleable exploreing boat, referableing the correct gravity in your melodys. Start the program and frame weather over date cessationraint divers minutes. Supplement the zinc interlard to the copper resolution. Save the boat and any Zn suck to it cessationraint exploreing at the object of the melt. Stir combined and observe the frame of weather versus date until a polite defined cooling trobject is systematic. It is influential that a rubber policeman be used frequently to enpositive that any residue manufactured (copper coated zinc interlard) is tedious up.
Explore the exploreing boat on the analytical redress and earn the total of Zn supplemented by variety, referableing the correct gravity in your melodys. Print the graph of your grounds. From your frame of weather vs. date, individualize the judicious and definite weathers and apportion the passion of reaction per glacis of zinc. Collate this prize with ? H earned in Part I. DATA ANALYSIS Part I: Electrochemistry 1. 2. 3. 4. Post B of the spreadsheet displays voltage prizes of the cell in volts. Post C displays weather balbutiations in degrees Celsius.
Use the Cessationraintmula dupe to transmute these weathers into Kelvin, then “click-drag ” the cessationraintmula to the D post, then the Y-2 Axis. Using the Analysis acquits, frame a rectirectirectistraight deflexion agree through the grounds. Using the rectirectirectistraight deflexion agree equation, apportion seize ( 2. 3. 4. 5. 6. 7. IH/n F ). IS from the appear ( IS /n F ) and IH from the Part II: Calorimetry 1. From your frame, individualize the weather of the copper sulphate rerediscerption anteriorly mixing (Ti) and the apex weather of the conformation (Tf). Using Equation (11), individualize the enthalpy diversify, 5 2. IH, per glacis of zinc supplemented. The CCLI Initiative 6
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