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Investigating the effects of changing the concentration of different solutions on the refractive index and the conductivity

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Physics Investigation --- Investigating the effects of changing the concentration of different solutions on the refractive index and the conductivity Content Aim P.2 Summary P.2 Risk assessment P.2 Information on errors / uncertainties P.2 Background P.3-7 Refractive index P.3-7 Diary P.7-13 Day 1 P.7 Day 2 P.7 Day 3 P.8 Day 4 P.9-10 Day 5 P.10-11 Day 6 P.11-12 Day 7 P.12 Day 8 P.12-13 Analysis P.13 Background P.14-15 Conductance P.15 Dairy P.15-16 Day 9 P.15 Day 10 P.16 Analysis P.16 Evaluation P.17 Conclusion P.17 Bibliography P.18 Appendix P.19-24 1 P.19 2 P.20 3 P.21 4 P.22 5 P.23 6 P.24 Aim The main aim of this investigation is to find out how some of the properties of solutions change when their concentration is altered. Summary When I was told that we were going to do this practical investigation, I struggled for a while not knowing what to do. But as I searching more and reading more about A Level experiments, they conjured up lots of different ideas in my head. When it came to the time for our plan, I decided to investigate the effect of changing the concentration of different solutions on the refractive index. At the beginning, I had some troubles in choosing suitable equipment. When I tried out some trials, they seemed alright. However due to a few problems arose, I had to change my idea slightly. So instead, I investigated the effect of changing the concentration of different solutions on the conductance of the solutions. Risk Assessment I have considered the risk that might occur during the investigation before I actually start my investigation. As I am going to deal with mainly salt and sugar, these substances and the solutions formed are neither irritant nor corrosive nor carcinogenic etc. Besides, most equipment that I am going to use is normal laboratory equipment like beaker, glass rod, watch glass ... ...read more.


Volume of water Upper boundary of the maximum moles of salt to be put in = 0.5346 mol 100 cm-3 ? (50 � 1) cm3 = (0.2673 � 0.0053) mol Lower boundary of the maximum moles of salt to be put in = 0.5288 mol 100cm-3 ? (50 � 1) cm3 = (0.2644 � 0.0053) mol Maximum mass of salt to be put in = Maximum moles of salt ? RMM of salt Upper limit of maximum mass of salt to be put in = (0.2673 � 0.0053) mol ? 58.4 g mol-1 = (15.6103 � 0.3095) g Lower limit of maximum mass of salt to be put in = (0.2644 � 0.0053) mol ? 58.4 mol-1 = (15.4410 � 0.3095) g So by doing all the calculations above, I found the maximum mass of salt to be dissolved in 200 cm3 of water is (62.10 � 0.03) g. And by using equations like: Moles = Mass / Relative molecular mass Concentration = Moles / Volume I found the saturation of salt solution to be 0.5317 � 0.0029 moles per 100 cm3. Day 5 As I have decided to use 50 cm3 of water each time, after knowing that the saturation of salt solution, I worked out the amount of salt can be dissolved in 50 cm3 with the upper limit to be (15.6103 � 0.3122) g and the lower limit to be (15.4410 � 0.3088) g. So I tried to added different mass of salt into 50 cm3 within 15 g and allowed all the salt to dissolve with the help of a glass rod. Once all the solutions had been prepared, I actually carried what I wanted to find, i.e. the refractive of these solutions using the same method as I used in day 3 for water. The table of results of (r1-r3) & (r1-r2) values collected from those salt solutions are recorded in Appendix 1. ...read more.


2) equipment not available --- this is a really big limitation to me as the text book suggests to use travelling microscope to find the refractive index. However, due to the travelling microscope having a scale the wrong way round, I have had to use binocular microscope. And it is because of this binocular microscope which gave me the values of R1 - R2 equalling to 0, the refractive index couldn't be found. 3) temperature --- temperature could be another factor that have affected the results obtained, as a higher temperature in some solutions would have caused more salt or sugar to be dissolved than in room temperature. I have tried to eliminate this error by carrying out all my experiments in the same laboratory, however, the temperature in the same laboratory can still differ from day to day even the difference shouldn't be much. Conclusion To conclude, I wouldn't say that I have actually proved anything or even I have deduced a law simply because what I found in both parts of my investigation, refractive index and conductance, don't seem to match the theory and was totally unexpected. So far, I found out that for salt solution at a magnification of 28, as its concentration increases, the density of the solution is increasing; the angle of refraction of light ray bends more towards the normal, which gives a bigger refractive index. However, for sugar, there isn't a pattern for its refractive index as its concentration is increased. Besides, as the magnification is adjusted to 56, the refractive index for both salt and sugar solution at any concentration is nothing. About the effect of varying the concentration on the conductance, sometimes increases the concentration results in having more freely charged ions to move towards electrodes giving a higher conductance and sometimes an increase in concentration results in reducing the ability for these ions to move around. And further more, even I have in fact discovered anything new or anything beyond the theory or anything that the theory couldn't explain, without carrying out lots and lots of repeats, everything is still a mystery. ...read more.

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