# Experiment to Investigate the Effect of Concentration on Rate of Reaction Essay Sample

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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 copper electrode with pungent smell. After the reaction, the color of zinc stripe changed from silver grey to black. The color of copper stripe became darker brown. When the H2SO4 solution is diluted, the change of the stripes’ color becomes slighter. Figure 1: graph concentration of H2SO4 solution versus electronic current. Figure 1: graph concentration of H2SO4 solution versus electronic current.

This figure shows the relationship between concentration of electrolyte H2SO4 solution and the electronic current of this Cu-Zn voltaic cell. The electronic current increases with the concentration electrolyte.

Samples of calculation
vdiluted H2SO4=voriginal H2SO4+vwater
=5±0.2+35±0.2
=(5+35)±0.2+0.2
=(40±0.4)mL
=(0.04±1%)L
nH2SO4of diluted H2SO4solution=c×v
=(9±1%)×(5±0.2)×10-3
=(9±1%)×(5±0.25)×10-3
=(9±1%)×(5±12.5%)×10-3
=(0.045±13.5%)mol
cdiluted H2SO4=nH2SO4of diluted H2SO4solutionvdiluted H2SO4
=0.045mol(±13.5%)0.04L(±1%)
=(1.125±14.5%)molL-1

Conclusion and Evaluation
The experiment shows that the current of Cu-Zn voltaic cell will increase with the concentration of electrolyte H2SO4 solution. It is because that when the concentration of sulfuric acid is increased, the number of ions is increased. There will be more ions carrying electric charge. Then, electric current is increased. There are a number of changes which can help to improve my experiment and makes the results more reliable. For example, the ammeter I used in this experiment is not so accurate. A better machine with smaller uncertainty can make the results more reliable. When water and sulfuric acid solution are added together, heat is released. It may be better to measure the temperature of the mixed solution and waiting for the temperature to fall to the room temperature.

Then the results will be more accurate. The copper and zinc stripes are not pure enough. Impurity in the stripes may consume some of the current of the voltaic cell. The result will be less than what it should be. Purer stripes can improve the experiment results. During the experiment, pungent smell is released. It is because that some acid mist came out with the hydrogen gas. There may be some toxic substance in the mist. To improve this situation, a porous board wetted by NaCO3 solution should be used to fix the electrodes instead of the cystosepiment. A porous board can let the hydrogen gas come out and basic NaCO3 solution in it can react with the acidic impurities in the gas and reduce the pungent smell.

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