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Investigate how the concentration of 10 ml of hydrochloric acid affects the rate of reaction of 3g of marble chips.

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Introduction

PLAN Section 1 Brief statement of investigation In this investigation I aim to investigate how the concentration of 10 ml of hydrochloric acid affects the rate of reaction of 3g of marble chips. Risk assessment Care must be taken when some of the higher concentrations of hydrochloric acid are used (1 molar, 0.9 molar etc.) and goggles must be worn at all times to protect the eyes. Also when handling any glass objects, care must be taken, as many of them are very delicate such as the long, glass, measuring cylinder. Independent variables The independent variable is the concentration of the 10ml of hydrochloric acid. I have chosen this variable since it is easy to measure compared to other possible variables (it would be much harder to measure marble chips as precisely). Dependent variable The amount of gas produced in 3 minutes when the marble chops are placed in the hydrochloric acid. I think that this is a good on e to choose since I expect it to be closely related to the independent variable. Number and range of readings I will be making 3 readings for each concentration (1 every minute for 3 minutes) and there will be 10 different concentrations. Section 2 Prediction I predict that as the concentration of the hydrochloric acid is increased, the rate at which the marble chips react will increase. I also think that as the concentration of the hydrochloric acid is increased, the amount of gas that the hydrochloric acid can react from the chips will increase although it may be hard to observe whether this statement is true or false in this investigation. ...read more.

Middle

The graphs showing the higher concentrations of hydrochloric acid have a more curved curve, which shows that they are slowing down at a greater rate than the reactions involving lower concentrations of hydrochloric acid. Section 3 Conclusion based on section 1 & 2 above From my results I conclude that as the concentration of the hydrochloric acid is increased, the rate at which the marble chips react increases and that the anomalies are due to differences in surface area. I have also noticed that the reactions involving the higher concentrations of hydrochloric acid slow down at a higher rate. Relate conclusion to detailed scientific knowledge When the concentration of the hydrochloric acid is increased, there is more 'pure acid' to react with the marble chips because the rest of the solution is water (and the hydrochloric acid is dilute in the first place). This means that with a higher concentration of hydrochloric acid, more gas is produced from the reaction within the 3-minute time. The surface area is the main problem area. The surface area of the chips has a big effect because for example you may have one large chip weighing 3g and many tiny chips collectively weighing 3g. The larger the surface area of the 3g of chips, the more area the hydrochloric acid has to react on. In this case it would mean that the large chip would react very slowly and the small chips would react very quickly. ...read more.

Conclusion

This was actually slower to react than 0.5 moles. The reason that it was so anomalous was because it may have been a large chip therefore with a smaller surface area than multiple small chips. Support for a firm conclusion Looking at the graphs, I think that I have support for a firm conclusion in that the curves of the graphs follow a pattern and they support my prediction. However I am not sure how true my results will be outside of the range within which I carried out my investigation. On the graphs it is noticeable that the curves on them get less and less steep until they become upwards sloping. If I carried on the experiment within concentrations down to say, 0.01 moles I may find that there is a point when the marble just doesn't react at all. At the other extreme, if I used an acid that was about 1000 moles it would probably produce less gas than 20 moles so if I had continued the experiment upwards I would have found the concentration of acid that produces the most gas. Improvements to the method To improve my range of results I could have done about 10 readings in a space of about 5 minutes so I will get a more accurate curve for my graphs and I would find out what would happen in a longer time span. Additional evidence To give extra support for my results I could carry out the same experiment but with a different substance such as magnesium. This would both improve the accuracy (see accuracy section) and give extra support for my results. 1 ...read more.

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