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To investigate factors affecting the rate of electrolysis when electrolysing a potassium nitrate solution.

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Introduction

Chemistry Investigation- Electrolysis Aim To investigate factors affecting the rate of electrolysis when electrolysing a potassium nitrate solution. Theory: When electrolysing a potassium nitrate solution, there are four ions present: 1. H+ From water (H- H+ + OH- ) 2. OH- From water (H2O H+ + OH- ) 3. K+ From Potassium Nitrate 4. OH3- From Potassium Nitrate H+ and K+ compete for electrons at the cathode. K+ is the more stable of the two, so therefore it is H+ that reacts: 2H+ (aq) + 2e- --> H2(g) OH- and NO3- compete to lose electrons at the anode. NO3- is more stable, therefore OH- will react. 0H- (aq) --> 0H- (aq) + e- Uncharged OH is unstable so it reacts: 40H- (aq) --> 2 H2O(1) + O2 (g) When electrons are released by OH- ions when they react are pushed round the circuit by the power supply into the gaps left by the electrons reacting with the H+ Ions: Therefore the rate of electrons flowing round the circuit is dictated by how fast the reactions are occurring. This means that current can be used as a measure of the rate of reaction Variables There are several variables I could change, these are: * Voltage. ...read more.

Middle

For my second variable- potassium nitrate concentration, I can make this prediction based on my theory above. This variable should have an effect on the ROR because with less potassium nitrate in the solution, the electrons are less likely to cause a reaction, so the rate of reaction will be slower, and this is basically the collision theory. So in summary I predict that the greater the concentration of Potassium Nitrate, the greater the ROR. I predict to see two graphs similar to these. Equipment * Potassium Nitrate * Water * Measuring cylinder * Power supply * Carbon electrodes * Ammeter * Beaker Method I will set up the equipment up as shown below: I will then turn the power supply and take readings with the ammeter for the different voltages in my range. I will do the same for my second variable, except I will vary the concentration of the potassium nitrate each time. I will then record my results: Results 1st Variable; 100ml 100% concentration: Volts (V) Current (amps) (repeat 1) Current (amps) (repeat 2) 2 0 0 4 0.2 0.4 6 1.2 1.4 8 2.0 2.4 10 3.4 3.7 12 4.6 4.8 2nd Variable; 8V 100ml potassium Nitrate solution: Potassium Nitrate Concentration (% out of 100ml) Current (amps) (repeat 1) Current (amps) (repeat 2) ...read more.

Conclusion

If I was going to continue with this investigation I would go on to see how Temperature affects the reaction, I would do this by heating the reaction and measuring the temperature and current. I could also change this experiment by recording a different variable. I could measure the gas given off by the reaction, like below: My results are consistent when drawn up on a graph; generally they show consistency in my results, which leads me to believe that my results are accurate. I feel most of my results are accurate, although there are a few anomalies, these could be due to any number of reasons, I have listed some below. * The measuring equipment I used may not have been as precise as more expensive equipment used in industry. This may add to the inconsistency of my results. * My measuring out of solutions of potassium nitrate and water may not have been 100% accurate. * Experimental error- I may have made a small mistake in reading the ammeter or made another small mistake, which could affect my results. * Temperature - the potassium nitrate may not have been at a constant temperature, if the temperature rose, then my results would have been affected. My results support my conclusion, so I can say they are reliable. Look at my graph, it shows my results support my conclusion. ...read more.

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