Experiment to Investigate the Effect of Concentration on Rate of Reaction

Topics: Electrochemistry, Sulfuric acid, Battery Pages: 5 (1104 words) Published: January 10, 2013
Experiment to investigate the effect of concentration of electrolyte on the current of voltaic cell

Aim
The aim is to identify the relationship between the concentration of H2SO4 solution and the current of Cu-Zn voltaic cell. Hypothesis
My hypothesis is that the greater the concentration of sulfuric acid the bigger the current of the voltaic cell. In a voltaic cell, chemical energy is concerted to electrical though the oxidation and reduction happen on the electrodes. Current will not flow through pure water. There must be electrolytes dissolved in it before electricity can pass through it. When the concentration of sulfuric acid is increased, the number of ions is increased. There will be more ion carrying electric charge. Then, current is increased. Introduction and Background

This is the Cu-Zn voltaic cell used in the experiment. Zinc has higher reactivity and it is more likely to loss electrons. Thus, electrons flow from Zn electrode to Cu electrode. Copper stripe is the positive electrode. Zinc stripe is the negative electrode. Reaction happened on each terminal:

Positive terminal: Zn-2e-→Zn2+
Negative terminal: 2H+2e-→H2
It is assumed that bubbles (hydrogen gas) will come out from copper electrode. It is assumed that zinc and copper stripes are pure.
Classification of variables
Dependent variables
Current of the voltaic cell
Independent variables
Concentration of sulfuric acid solution
Controlled variables
Size of the copper and zinc stripes
Material of the electrodes
Distance between the electrodes during reaction
Volume and temperature of sulfuric acid solution

Materials and Apparatus
1cm×4cm Cupper stripes
1cm×4cm Zinc stripes
1 Ammeter (±0.015)
2 Wires
2 Beakers (50mL)
9molL-1 H2SO4 (±1%)
1 Cylinder (25±0.1mL)
Cystosepiment with two holes
Method
1. Dilute the 9molL-1 H2SO4 by pouring 5mL sulfuric acid solution and 35 mL water in a beaker and stir. 2. Use two wires to connect the copper stripe and zinc stripe to the ammeter. Copper stripe is the positive electrode and should be connected to the positive electrode with maximum deflection of 0.6A. Zinc stripe should connect to the negative terminal. 3. Penetrate the stripes into holes of the cystosepiment to fix their position in the electrolyte. Minimize the position between the two stripes in order to maximize the current of the voltaic cell, but do not let them touch. 4. When you first out the electrodes in the electrolyte, the pointer of ammeter will wave violently. After some time, record the number ampere before the pointer start falling to the original point. 5. Repeat step 1 to 4 for tree time.

6. Repeat step 1 to 5 with more diluted sulfuric acid. Control the total 40mL volume of solution. Increase the volume of water and reduce the volume of original 9molL-1 H2SO4.

Rough Collected Data
Quantitative observations:
Concentration of H2SO4 solution: 9molL-1
Volume of H2SO4: 40mL
The solutions were supplied by the teacher with the given error of 1%. A cylinder was used to deliver the solutions; hence the error was estimated at 0.2 cm3.

| Volume of H2SO4(±0.2mL)| Volume of H2O(±0.2mL)| Volume of diluted H2SO4 (±1%mL)| 1| 5| 35| 40|
2| 4| 36| 40|
3| 3| 37| 40|
4| 2| 38| 40|
5| 1| 39| 40|

| Concentration of diluted H2SO4(molL-1)|
1| 1.125|
2| 0.900|
3| 0.675|
4| 0.450|
5| 0.023|

| electronic current (A)(±0.015A)| Average electronic current (A)(±0.015A)| 1| 0.21| 0.22| 0.22| 0.217|
2| 0.18| 0.18| 0.18| 0.180|
3| 0.14| 0.15| 0.14| 0.143|
4| 0.12| 0.12| 0.12| 0.120|
5| 0.11| 0.09| 0.11| 0.103|

| Concentration of diluted H2SO4| Electronic Current (A)(±0.015A)| 1| 1.125| 0.217|
2| 0.900| 0.180|
3| 0.675| 0.143|
4| 0.450| 0.120|
5| 0.023| 0.103|

Observations:
When I put the electrodes in 1.125 molL-1 H2SO4 solution, the reaction is violently. Many bubbles formed at the...
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