Experiment 4

Experiment 4 - Experiment 4 Electrochemistry and Vitamin C...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Experiment 4: Electrochemistry and Vitamin C Abstract The experiment used redox titrations and the concept of cell voltages (determining a reaction’s spontaneity) to find the amount of ascorbic acid in a vitaminc C tablet. The first part involved observing the activity series between a zinc solution against a copper solution, with differing concentrations, and that between identical copper solutions, also with differing concentrations. For the zinc and copper series, the following series were prepared: 0.1 M ZnSo 4 vs 0.1 M CuSo 4 , 0.1 M ZnSo 4 vs 0.001 M CuSo 4 , and 0.001 M ZnSo 4 vs 0.1 M CuSo 4 , which provided cell voltages of 1.098 V, 1.42 V, and 1.072 V respectively. For the dual copper series, the following series were prepared: 0.1 M CuSo 4 vs 0.001 M CuSo 4 , 0.1 M CuSo 4 vs 0.0001 M CuSo 4 , 0.1 M CuSo 4 vs 0.00001 M CuSo 4 , and 0.1 M CuSo 4 vs 0.000001 M CuSo 4 , which provided cell voltages of 0.0298 V, 0.0343 V, 0.0400 V, and 0.0454 V, respectively. The second part involved the determination of the amount of ascorbic acid in a vitamin tablet through redox titrations. A thiosulfate solution was standardized to have a determined concentration of 0.1303 M . And it was used to determine that there was 505.7 ± 40.4 mg which was very close to the nominal value of 500 mg. Introduction The purpose of this experiment is to determine the amount of ascorbic acid present in a vitamin tablet through the use of redox titrations. The reactions involved in this experiment must go to completion in order to use stoichiometry to find the amount of ascorbic acid present. The reactions used are known to be favorable by looking at the equilibrium constants. With a K of more than 1, the product will go to completion and visa versa. Another way to determine whether a reaction goes to completion or not and is related to the equilibrium constant as well is the cell voltage, E ° cell . This field of study is known as electrochemistry. In redox reactions, a species is oxidized (loses electrons) while another species is reduced (gains electrons). If the species are separated to represent what type of half reaction it undergoes, it can be represented by a value known as standard reduction potential, E . The spontaneity of the reaction can then be determined by adding the respective potentials together. Using the expression ΔG=-nFE , if the cell potential, E ° cell >0 then it means that the reaction will go to completion and visa versa if E ° cell <0. This can be observed by separating the species in a set-up called electrochemical cells. With the species separated, oxidation and reduction are separated as well. The location where the species is reduced is called the cathode and for oxidation is the anode. But to see the interaction between the two species, they must be connected by a salt bridge which facilitates in the transfer of electrons. This creates a current which can then be observed with a pH meter with the ability to read voltage. When observing the cell voltage between species, it is important to note that the concentrations of
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/15/2008 for the course CHEM 100A taught by Professor Dai during the Fall '06 term at UCSD.

Page1 / 11

Experiment 4 - Experiment 4 Electrochemistry and Vitamin C...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online