The research question that this report is going to discuss is “What is the relationship between concentration of hydrochloric acid (HCl) and the rate of diffusion? ” My hypothesis for this research question is that change in rate of diffusion will be observed when the agar blocks are placed in solutions of different concentrations of HCl. As the concentration of HCl increases, the rate of diffusion will also increase due to the steeper concentration gradient created.

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To investigate the change in rate of diffusion when different concentrations of HCl are used, I used agar blocks that are stained with universal indicator that would change from green to pink when exposed to HCl. To prepare the agar blocks, I used knife and ruler to acquire 5 agar blocks with equal dimensions of 3. 0cm by 1. 0cm by 0. 5cm. Then I prepared 5 different concentrations of HCl with equal volume of 5cm^3 in test tubes, which were 0. 0M. 0. 2M, 0. 4M, 0. 6M, 0. 8M and finally 1. 0M of HCl.

Then, I placed the agar blocks into respective test tubes, measuring the time taken for the agar blocks to turn from green to completely pink. This was repeated 2 more times, having 3 set of readings in total. The results collected showed an increasing trend in the rate of diffusion as the concentration of HCl increased. This clearly supported the hypothesis I derived at. (227 words) ? Content Page Abstract2 Content Page3 Introduction4 Research question:4 Hypothesis:4 Introduction (2)5 Literature Review5 Methodology6 Results8 Results (2)9 Discussion10

Limitations11 Improvements11 Conclusion12 Bibliography13 ? Introduction Research question: How does change in concentration of hydrochloric acid (HCl) affect the rate of diffusion through the agar blocks which contain starch stained with universal indicator, while keeping surrounding temperature, the surface area to volume ratio of agar blocks used and the volume of solution to which the agar blocks were placed constant? Hypothesis: Change in rate of diffusion will be observed when agar blocks are placed in solutions of different concentrations of HCl.

As the concentration of HCl increases,

Page 2 Concentration of HCL affecting surface area to vol ratio Essay

the rate of diffusion will also increase due to the steeper concentration gradient created ? Introduction (2) Literature Review Diffusion is known as the net movement of particles from a region of higher concentration to a region of lower concentration along the concentration gradient. There are few factors that affect the rate of diffusion, the time taken for both regions to have equal amount of particles. One of them is temperature.

It is known that temperature has the greatest effect on diffusion rates and is the easiest of the factors to change. Increasing the temperature increases the diffusion rate by adding energy to each particle. This is because particles with more energy can move to the region of lower concentration with more speed and more easily. Similarly, lowering the temperature will lower the diffusion rate by lowering the energy of each particle. Another important factor that changes the rate of diffusion is the concentration gradient, which we will be exploring in this experiment.

The rate of diffusion depends on the difference between concentrations across the region of lower concentration and higher concentration, with steeper concentration differences resulting in higher diffusion rates (Simon 2013). This can be explained by Fick’s Law, which can be summarised by this equation: Rate of diffusion is proportional to(surface area x difference in concentration )/(Length of diffusion path). From the equation derived from Fick’s Law, it is clearly seen that the difference in concentration (concentration gradient) will increase the rate of diffusion (Michael Kent 2000).

This theory can be used to explain real life situations, like how human lungs take in oxygen and give out carbon dioxide in a split second. It is due to the great difference in concentrations of both gases (very steep concentration gradient) that allows relatively fast rate of diffusion. For instance, when breathing in, the concentration of oxygen in alveoli is very high compared to that in the blood vessels surrounding the alveoli. Thus, rate of diffusion is great, allowing oxygen to diffuse as fast as possible. (BBC 2013) Methodology Table 1.1-Table of variables and how it is controlled VariablesDetails of variablesHow it is controlled Independent VariableConcentration of HClConcentration of HCl is controlled by the amount of distilled water added to HCl. For example, in order to achieve a concentration of 0. 2 moldm^(-3), 1. 0 cm^3 of 1 mol of HCl is added, with 4 cm^3 of distilled water added. Dependent VariableRate of Diffusion The time is taken by a stopwatch until the agar block turns pink in colour completely. Controlled VariableTemperature of the surrounding Surface area to volume ratio of the agar blocks

Volume of solution to place the agar blocks into. Temperature is set at an air-conditioned room in a Biology lab The agar blocks are cut into same length, same breadth and same height (3. 0 cm by 1. 0 cm by 0. 5cm), thus having the same volume and surface area. This ensures the ratio is the same. The volume of solutions used is kept the same at 5. 0cm^3. Table 1. 2-Apparatus used in the experiment Apparatus QuantityUncertainty 2% Starch Agar (Universal Indicator stained)– 1. 0 M Hydrochloric Acid (aq)– Deionized Water– Stop Watch2±0. 01s

This might be due to the inaccurate cutting of the dimension of the agar blocks. It could also be due to our inability to decide whether the agar blocks have turned completely green to pink in colour. Thus, the calculated rate of diffusion could have changed. Limitations Some of the results were not as accurate as it was difficult to see whether the agar blocks have turned entirely pink in colour. Some of the agar blocks still had strips of green in them when we removed it from the solution and cut it. This could have affected the time taken for the agar blocks to turn entirely pink and thus, affecting the rate of diffusion.

The temperature of the solutions containing the agar blocks might not be constant throughout the whole experiment. This can be due to holding of test tubes with our hands and also putting it down again several times. The heat from the hand might get transferred and the temperature might be altered. This can affect the time taken for the agar blocks to turn completely pink, as higher temperature induce faster rate of diffusion. Some of the results are not very accurate as the surface area to volume ratio was not constant for all the agar blocks tested.

One of the reasons is due to the limited amount of agar blocks that were allocated for each bench. Another reason is that it was difficult to use the knife provided to cut the agar blocks in a straight manner and as accurately. This limitation can affect the time taken for agar blocks to turn pink, followed by the rate of diffusion, as some blocks are bigger while some are smaller than the others. Improvements In order to make sure that the agar blocks have turned entirely pink, use a light and put it in a white background where the colour changed is more visible.

Then, the calculated rate of diffusion will not be affected. Place the test tubes in a water bath where the temperature can be kept constant at the temperature of tap water. This way, the calculated rate of diffusion will not be affected. Lastly, use a stamp with all the desirable dimension of the agar blocks measured. This way, not only is it convenient, it also helps us acquire the accurate dimensions of the agar blocks, having the same surface area to volume ratio for all the agar blocks. Then, the calculated rate of diffusion will not be affected. Conclusion

In conclusion, the readings and the derived results in the form of tables, and line graph support my hypothesis, which is: Change in rate of diffusion will be observed when agar blocks are placed in solutions of different concentrations of HCl. As the concentration of HCl increases, the rate of diffusion will also increase due to the steeper concentration gradient created. With the derived conclusion, it shows that in order for rate of diffusion to be greater, higher concentration of the solution must be used, so that the concentration gradient is steeper.

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