Concentration Current Voltage Resistance 2 example essay topic

This experiment aims to investigate the resistance of brine soaked paper when an electrical current is passed through it. Planning: Previous experiments have taught me that the electrical resistance will rely on several key variables. These include the length of paper, its thickness but most importantly the number of sodium and chlorine ions carrying the charge. Knowing this, I have decided to investigate the concentration of brine in this experiment. To provide an accurate prediction, I must research into the scientific details in this experiment and recall information from previous investigations. This will give me a greater understanding of the experiments implications and likely results.

Ionic compounds do not have a molecular structure, but form a three-dimensional array of ions called a crystal lattice. In a crystal of sodium chloride, the ions are arranged so that each Na+ ion is surrounded by six Cl- ions and vice versa. Because the ions are held rigidly in place by the electrostatic attractions between any one ion and the oppositely charged ion surrounding it, these compounds tend to be very brittle. They do not conduct electricity when in a solid state, since the ions are not mobile. However, when in solution or in the molten state, ionic compounds will conduct electricity by the movement of ions.

In this investigation, two electrodes will be placed on paper soaked in brine and an electrical current will be applied. The sodium chloride is in a solution with water so that the ions are free to disassociate. The sodium ions should migrate to the negative electrode and the chloride ions migrate to the positive electrode, causing an electrical current to flow. Having singled out the mos influential factor, and researched into the formation and qualities of the sodium chloride compound, I have formed a prediction. I predict that the higher the concentration of sodium chloride in the brine solution, the lower the resistance. This prediction is based upon the fact that at a higher concentration, there will be more sodium chloride ions creating lower resistance.

Method: 1. Connect the circuit, ensuring that the voltmeter is in parallel with the brine soaked paper. To investigate the resistance of brine soaked paper; I will set up an electronic circuit. I will utilise a battery, variable resistor, wire, voltmeter and a milli-ammeter. I am using a milli-ammeter because the difference in current is likely to be minute and this will give me a more accurate reading. I am using a variable resistor so that I can take several readings (repeating my results) to form an accurate investigation.

2. Measure out 10 ml of solution in six test tubes. The salinity will be varied by diluting a 1 M solution of brine to different ratios of salt to water. To obtain accurate readings, the same amount of brine will be used for each result (10 ml). This will be measured using a measuring cylinder. 3.

The paper will be placed in a test tube of brine for the specific time of five seconds ensuring that the paper is completely coated in brine. The paper will only be soaked for a specific time because over a longer period paper will absorb a greater amount of liquid. By controlling the time, I can create a fairer experiment. The amount and type of paper will be identical for each reading.

I will use a 62 cm rectangular sized piece of paper. If I used differing sizes of paper then my results would be inaccurate as more brine could be absorbed or the greater amount of paper would create a higher resistance. 4. The brine soaked paper will be connected into the circuit using crocodile clips. To prevent contamination or loss of brine, forceps will be used to transfer the paper from the test tube into the circuit. 5.

To discover the resistance of the brine soaked paper; I will record the voltage and current at each concentration repeating each reading three times and then formulate the resistance using the formula: Resistance = Voltage Current will then take the average of my readings to ensure accurate results and reduce the effect of any inaccuracies. Obtaining Evidence / Analysing Evidence And Drawing Conclusions: I have tabulated the results of the experiment so that any patterns will become more apparent and I can distinguish whether my hypothesis was correct. The concentration column in the table states the percentage of brine as opposed to water used to test each reading. 1. Concentration Current Voltage Resistance 2. Concentration Current Voltage Resistance After taking these readings, I realised that although both tables 1 and 2 show a similar trend, the actual figures are very different.

They vary from a resistance of 468 ohms at one reading to 235 ohms at the same concentration. Although I had been careful to keep the same brine for each reading and controlled the other key variables, the readings had been taken on separate days. The milli-ammeters I used were different causing the recorded current to also be different. I decided to repeat the entire experiment again repeating readings on the same day (See Table 3). I have formulated the readings into a graph to help illustrate any patterns in the data, find the anomalous results caused by mistakes in the investigation and try to determine the validity of my original prediction (See Graph 1). The graph illustrates a very distinct relationship between the concentration of salt and the resistance of the brine soaked paper.

It depicts that brine is inversely proportional to resistance. The greater amount of brine, the lower the resistance. When the paper was soaked in water only (concentration 0%), there was a very high resistance yet some current passed. This may have happened because tap water was used and it may have contained traces of metal, which could carry current. At a concentration of 20%, the resistance dramatically reduced decreasing from 390 ohms to 48 ohms. It then steadily reduced as the concentration increased producing the curve on the graph.

These results appear to prove my original hypothesis The higher the concentration of sodium chloride in the brine solution, the lower the resistance, as all of my readings reflect this prediction. However, to be certain of this, I would need to form a more detailed investigation, correct any anomalous results and create an even more accurate and fair test. Evaluating: My results seem reliable as the data produced a graph with a clear line of best fit. However, discrepancies could have caused slight inaccuracies in this investigation. As I mentioned earlier, I used tap water to dilute the brine to gain different concentrations.

This meant that with no salt, some current was able to pass due to the impurities in the water. To create a fairer test, I should have used distilled water. In this experiment, I took readings at six different concentrations repeating each three times. If I were to repeat the entire experiment, I would be sure to record at least ten readings repeating at each concentration five times.

To enable readings that are more accurate a more advanced ammeter could be used because the difference in current is small. The readings taken from the ammeter I used, were only for three significant figures and so inaccuracies occurred. When I repeated results, the readings were similar however, as I was working with milli-amps, slight differences increased after the resistance was formulated. By observing the graph, you can see that in this investigation there were no obvious anomalies. As I repeated and averaged my results, any minor inaccuracies were cancelled out. I feel that overall this investigation was accurate and it opens up further possibilities for future experiments.

These include investigating whether the thickness of the paper or length of paper would greatly influence the resistance.