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Investigating the effect of ion concentration in electrolytes on the potential difference in a voltaic cell

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Introduction

Investigating in the effect of ion concentration in electrolytes on the potential difference in a voltaic cell Introduction When two electrodes made of different metals are connected together in a voltaic cell, the chemical energy present is converted into electrical energy and an electromotive force is generated. This force, called the electrode potential, is normally measured under standard conditions, which is 298K, 1 mol dm-3 solution for the electrolyte. However when one measures the electrode potential in a voltaic cell, the conditions are often not at standard. The concentration of ions in the electrolyte solution affects the number of collisions the ions would have with the electrode. If the concentration increases, then probability of an ion coming into contact with the electrode increases. This experiment will mainly focus on the effect of changing ion concentration in electrolytes on the potential difference generated. Three different combinations of metals and electrolytes will be used to assess the general effect. Purpose The purpose of this investigation is to determine whether the concentration of ions in the electrolyte in a voltaic cell will affect the potential difference. ...read more.

Middle

and Iron Copper and Zinc Iron and Copper 0.20 0.00 0.00 0.00 0.16 +0.22 +0.91 +1.10 0.12 +1.60 +6.30 +1.90 0.08 +2.40 +10.00 +7.00 0.04 +2.90 +13.00 +12.00 In the above table, the percentage change is calculated as follows: Note: the uncertainty in this table is different for every result, but it is assumed that they all have the value of �0.01 Table 3: Overall average percentage change in voltage under different electrolyte concentrations/% Concentration/ mol dm-3 � 0.01 Percentage change in voltage 0.20 0 0.16 +0.74 0.12 +3.3 0.08 +6.5 0.04 +9.3 Note: the average is calculated by adding all three voltage values for a given concentration, and dividing the sum by three. The overall average was calculated across different metal and metal ion combinations. The rationale behind this is that although each combination for a certain concentration would generate a difference voltage, it should exhibit a similar trend across the different concentrations. Conclusion It seems from Graph 1 that as the electrolyte concentration increased, the potential difference decreased. This opposes the hypothesis, which states otherwise. By using data from this experiment alone, it seems that one can conclude as follows: the potential difference and electrolyte concentration have a negative correlation; as one increases, the other decreases. ...read more.

Conclusion

To improve the data collection, one can connect the voltmeter to a computer or calculator which has a graphing system. Connect the voltaic cell for exactly ten seconds, and by using the graph generated by the computer or calculator, one can calculate the exact average voltage generated. This would make the results more reliable, since it decreases the amount of subjectivity needed to record the data. A possible source of error as mentioned in the conclusion is in the distilled water. It may have been contaminated, or the filter in the ion exchange resin may need to be changed. However, note that if this were true then all the result should have been influenced in the same way. As a result the general trend would still be the same. To extend this investigation, one can investigate on the effect of temperature on the potential difference generated in a voltaic cell. This is an area worthy of further investigation because like the electrolyte concentration, temperature is one of the factors determining the electrode potential. Similar to the electrolyte concentration, the temperature and potential difference should have a positive correlation as well. 1 TutorVista. (2008). Nerns't equation. Available: http://www.tutorvista.com/content/chemistry/chemistry-iii/redox-reactions/nernst-equation.php. Last accessed 6 October 2009. ?? ?? ?? ?? Candidate Name: Teng, Eva Yi-Chun Candidate Number: 001407-038 1 ...read more.

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