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Determinación de la carga de un electrón por electrólisis

Químicos: * Solución de sulfato de cobre * Acetona * Ácido sulfúrico * Ácido sulfúrico diluido.

Químicos: * Solución de sulfato de cobre * Acetona * Ácido sulfúrico * Ácido sulfúrico diluido.

Objetivo: Determinar la carga de un electrón.
Equipo:
* Cubeta de electrólisis con armadura para conexión * Electrodos de cobre * Transformador * Conectores * Amperímetro * Cronómetro * Balanza electrónica * Probeta de 100 ml.
Diagrama:

Procedimiento:
Se limpiaron los electrodos con lija, se sumergieron en ácido sulfúrico y una vez secos, se midió la masa de cada uno. Se armó el equipo como en el diagrama 1. Se agregaron 200 ml de solución de sulfato de cobre. Se conectó la fuente de energía durante 5 minutos y se midió la corriente cada 15 segundos, intentando mantenerla constante. Se enjuagaron los electrodos, primero con agua destilada y posteriormente con acetona. Se dejó secar por unos minutos y luego se volvió a medir la masa. Se repitió el proceso 2 veces más. Se calculó la corriente promedio que ha fluido por el circuito en los tres casos. Se calculó la carga eléctrica que ha pasado por el circuito, los mol de iones de cobre formados o reducidos, mol de electrones transferidos y por consiguiente la carga de cada electrón.

Resultados: Tiempo en segundos (±1 s) | Corriente en A (± 0.05 A) | Masa inicial de Cu en g (±0.001 g) | Masa final de Cu en g (±0.001 g) | | | Cátodo | Ánodo | Cátodo | Ánodo | 15 | 0.90 | 3.321 | 13.382 | 3.350 | 13.377 | 30 | 0.90 | | | | | 45 | 0.90 | | | | | 60 | 0.90 | | | | | 75 | 0.90 | | | | | 90 | 0.90 | | | | | 105 | 0.90 | | | | | 120 | 0.90 | | | | | 135 | 0.90 | | | | | 150 | 0.90 | | | | | 165 | 0.90 | | | | | 180 | 0.90 | | | | | 195 | 0.90 | | | | | 210 | 0.90 | | | | | 225 | 0.90 | | | | | 240 | 0.90 | | | | | 255 | 0.90 | | | | | 270 | 0.90 | | | | | 285 | 0.90 | | | | | 300 | 0.90 | | | | |
Tabla 1: Datos crudos obtenidos en la primera repetición del experimento

Tiempo en segundos (±1 s) | Corriente en A (± 0.05 A) | Masa inicial de Cu en g (±0.001 g) | Masa final de Cu en g (±0.001 g) | | | Cátodo | Ánodo | Cátodo | Ánodo | 15 | 0.90 | 3.382 | 13.280 | 3.645 | 13.232 | 30 | 0.90 | | | | | 45 | 0.90 | | | | | 60 | 0.90 | | | | | 75 | 0.90 | | | | | 90 | 0.90 | | | | | 105 | 0.90 | | | | | 120 | 0.95 | | | | | 135 | 0.95 | | | | | 150 | 0.95 | | | | | 165 | 0.95 | | | | | 180 | 0.95 | | | | | 195 | 0.95 | | | | | 210 | 0.95 | | | | | 225 | 0.95 | | | | | 240 | 1.00 | | | | | 255 | 1.00 | | | | | 270 | 1.00 | | | | | 285 | 1.00 | | | | | 300 | 1.00 | | | | |
Tabla 2: Datos crudos obtenidos en la segunda repetición del experimento

Tiempo en segundos (±1 s) | Corriente en A (± 0.05 A) | Masa inicial de Cu en g (±0.001 g) | Masa final de Cu en g (±0.001 g) | | | Cátodo | Ánodo | Cátodo | Ánodo | 15 | 1.00 | 3.645 | 13.232 | 3.651 | 13.132 | 30 | 1.00 | | | | | 45 | 1.00 | | | | | 60 | 1.00 | | | | | 75 | 1.00 | | | | | 90 | 1.00 | | | | | 105 | 1.00 | | | | | 120 | 1.00 | | | | | 135 | 1.00 | | | | | 150 | 1.00 | | | | | 165 | 1.00 | | | | | 180 | 1.00 | | | | | 195 | 1.00 | | | | | 210 | 1.00 | | | | | 225 | 1.00 | | | | | 240 | 1.00 | | | | | 255 | 1.00 | | | | | 270 | 1.00 | | | | | 285 | 1.00 | | | | | 300 | 1.00 | | | | |
Tabla 3: Datos crudos obtenidos en la tercera repetición del experimento

Observaciones cualitativas: Los electrodos de cobre eran de un tono café oscuro con una capa de óxido que no se lograba quitar por más que se lijara. En el cátodo se llegó a recubrir por una delgada capa de óxido. El óxido de la capa que se formó en el cátodo no estaba muy fijada al electrodo y se caía en la solución al mover el electrodo, o se pegaba en la servilleta. El vinagre despedía su típico olor y era de un tono amarillento. El sulfato de cobre pentahidratado tenía una tonalidad azul intensa.
Para poder continuar se deben trabajar los datos crudos. Primero se calculará la diferencia de masa que ocurrió en el cátodo y ánodo de cada una de las tres pruebas. Luego se procederá a calcular el promedio de corriente fluida en las tres pruebas. Finalmente se obtendrá la carga eléctrica que fluyó por el circuito, los moles de iones reducidos/formados, el mol de los electrones transferidos y por consiguiente la carga de cada electrón.

Prueba | Diferencia de la masa de Cu en gramos (± 0.002 g) | Promedio de corriente fluida en A (± 0.05 A) | | Cátodo | Ánodo | | #1 | 0.029 | 0.005 | 0.90 | #2 | 0.263 | 0.048 | 0.95 | #3 | 0.006 | 0.100 | 1.00 | Promedio | 0.099 | 0.051 | 0.95 |
Tabla 4: datos calculados en base a los datos crudos Ahora se procederá al cálculo de la carga del electrón. Para eso se utilizará la siguiente fórmula: e-=I×tz×NAV×n Donde:
NAV=6.02×1023mol z= 2 t= 300 s ±1 s I= 0.95 A (± 0.05 A)
Cu2++2e-→Cu Cu→Cu2++2e-
Pero primero se deben calcular los moles de cobre en el cátodo y en el ánodo: cátodo n=0.099g Cu ±2.0%×1 mol Cu63.55 g Cu=1.6×10-3 mol (±2.0%) ánodo n=0.051g Cu ±3.9%×1 mol Cu63.55 g Cu=8.0×10-4 mol (±3.9%)
Ahora al cálculo de la carga del electrón: * Según el valor n del cátodo: e-=0.95 A ±5.3%×300 s (±0.333%)2×(6.02×1023mol)×(1.6×10-3 mol ±2.0%) e-=1.5×10-19 C (±7.6%) * Según el valor n del ánodo: e-=0.95 A ±5.3%×300 s (±0.333%)2×(6.02×1023mol)×(8.0×10-4 mol (±3.9%)) e-=3.0×10-19 C (±9.5%)

Conclusión:
El objetivo de este trabajo era determinar la carga elemental mediante la electrólisis. Como se puede ver, el objetivo fue alcanzado. Se obtuvieron dos valores para la carga elemental. El valor teórico de la carga elemental es el siguiente: e- = 1.6 * 10-19 C.
A continuación se presentará un cálculo del porcentaje de error para ambos valores obtenidos
% error= valor teórico-valor experimentalvalor teórico×100%

% error 1= (1.6 × 10-19 C)-(1.5×10-19 C (±7.6%))(1.6 × 10-19 C)×100%
% error 1=6.3%±7.6%
% error 2= (1.6 × 10-19 C)-(3.0×10-19 C (±9.5%))(1.6 × 10-19 C)×100%
% error 2=88%±9.5%
Se puede ver claramente que el valor experimental del cátodo se acerca más al valor teórico de la carga elemental que el valor experimental del ánodo. Los porcentajes de error muestran que en este experimento hubo una propagación de errores del tipo sistemático, ya que son mayores a los porcentajes de error instrumentales. De entre los errores presentes se pueden mencionar los siguientes:
La inestabilidad de la intensidad de la corriente eléctrica que fluía hasta el transformador. Para obtener una lectura correcta en el amperímetro se debía contar con ciertas condiciones adecuadas, una de esas era que no hubiera fluctuaciones por parte de la corriente eléctrica que llegaba al transformador. Una corriente eléctrica cuya intensidad se hubiera mantenido constante en las tres repeticiones habría dado datos más fiables. Yo no sé mucho acerca del área de la electricidad y las corrientes eléctricas, así que mi única sugerencia es contactar a la proveedora de energía eléctrica y pedirles que mantengan un suministro constante y estable. Otro error fue que parte de la capa de óxido formada en el cátodo quedaba en la servilleta a la hora de secar los electrodos. Esto tenía como consecuencia un dato de masa incorrecto con el cual se llevaba a cabo la siguiente prueba. Esto llevó a una propagación de errores desde la primera prueba. En mi opinión, los electrodos deberían ser sujetados por unas pinzas y dejarlos colgando en algún lugar a temperatura ambiental secando. Otro error relacionado a esto es la pérdida de parte de esa capa de óxido a la hora de remover los electrodos de la cubeta de electrólisis. Esto se debió a la anchura de los electrodos y la estrechez de la cubeta de electrólisis: siempre que se querían remover los electrodos, estos entraban en contacto con las paredes de la cubeta. La solución a esto es usar electrodos más estrechos o una cubeta más ancha, y ser más cuidadoso a la hora de removerlos de la cubeta. Un error en el experimento vino de la lectura del amperímetro. Hubo ciertas medidas que no se supo como leer, al igual que hubo momentos en los que no se sabía si se había puesto la medida correcta en el amperímetro. Lo mejor es aclarar todas las dudas acerca del uso correcto del con la maestra al principio. Un error muy grande tiene relación con el transformador. En los transformadores había una perilla que determinaba algo (porque sigo sin saber muy bien qué es) con respecto a la intensidad de la corriente que fluía hacia la cubeta. Se supone que la perilla debía estar en el mismo en los dos transformadores, pero hubo uno que lo tuvo del otro lado durante todo el experimento. No se sabe con certeza cuales son las consecuencias de este error o su magnitud, pero se sabe que se debe evitar a toda costa. Por eso es que hay que revisar desde un principio que todo lo que se utilizará en el experimento esté calibrado y ajustado de la manera en la cual se indique.

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...SUMMARY REPORT OF MARKS AND GRADES Session & Year: III Sem.B. Tech. Chemical- DEC 2011 Course No: CY 205 Course Title: Organic Chemistry Credits: 3-0-0(3) Department: Chemistry Name of the Instructor: Dr. Darshak R. Trivedi CLASS PERFORMANCE DISTRIBUTION STATISTICS ----------------------------------------------------------------------------------------------------------Class Size (No. of students) = 50 Class – Max. Marks (Xmax) = 85 Class – Min. Marks (Xmin) = 20 Class – Mean Marks (µ) = 59 Standard – Deviation (σ) = 18 Grades AA AB BB BC CC CD DD FF FA Cutoff Marks % 80 73 61 50 40 30 20 19 Attendance less than 75 % Number of Students 06 07 15 09 04 05 04 00 00 ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≤ ------ Signature of Instructor(s) (with date) Date: 7h Dec 2011 Signature of Secretary DUGC Signature of Chairman DUGC REPORTS OF MARKS and GRADES Session & Year: III Sem.B. Tech. Chemical- DEC 2011 Course No: CY 205 Course Title: Organic Chemistry Credits: 3-0-0(3) Name of the Instructor: Dr. Darshak R. Trivedi Course Category: BSc Sl. No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 Reg. No. 10CH01 10CH02 10CH03 10CH04 10CH06 10CH07 10CH08 10CH09 10CH10 10CH11 10CH13 10CH14 10CH15 10CH16 10CH17 10CH18 10CH19 10CH20 10CH21 10CH22 10CH23 10CH24 10CH25 10CH26 10CH27 10CH28 10CH29 1OCH30 10CH32 10CH33 10CH34 10CH35 10CH36 10CH37 NAME AAQIB H AZAAM ACHINT SANGHI ADITYA BATTU ADITYA NAIR AMIT ABRAHAM MATHAI ANANYA RAVI ANINDITA RAVIKUMAR...

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