Investigating How The Order Of Reaction Between Magnesium And An Acid Changes Using Different Acids And Varying Concentrations

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Investigating How The Order Of Reaction Between Magnesium And An Acid Changes Using Different Acids And Varying Concentrations

Sarah Taylor

Planning:

Reactions may take place at very different speeds. We need to understand what factors determine the rate of a reaction, and hence how to change the rate of a reaction. We then have the ability to control reactions more, and in industrial reaction the rate can be altered to suit the economics of certain manufacturing processes. Knowledge of how the rate of a reaction is determined is very important in providing evidence of that particular reaction mechanism.

In this investigation, I am going to investigate how the order of reaction with respect to the acid varies when magnesium is reacted with acids of different types. I am also going to determine how the concentration affects the order and rate of the reaction.

As a preliminary experiment, I took sulphuric, hydrochloric and ethanoic acid, and reacted them separately with magnesium powder. I used a conical flask which was connected by a rubber tube to a glass syringe, so that the amount of gas produced could be measured. This was simply a test to see roughly the quantity of gas produced by each, so that I could decide on appropriate concentrations for the acids, and also suitable time intervals at which to take the measurements. However, I found that when using sulphuric and hydrochloric acid, the reaction took such a short time before the whole 100cm3 syringe was filled, that it was impossible to accurately measure the rate. I decided to use instead of magnesium powder, magnesium ribbon, which has a much lower surface area, and so the reaction would be slower. I could have lowered the concentrations of the acids, but since I was using only 2M solutions and below already, the acids would have to be scaled down to such a low concentration to produce measurable results, that it would have become very inaccurate.

I have decided to use hydrochloric acid, which is a strong mono-basic acid, sulphuric acid, which is a strong di-basic acid, and ethanoic acid, which is a weak mono-basic acid. This provides a wide variety of acids for comparison. Each acid will be reacted with the magnesium at 0.5M, 1M, 1.5M and 2M concentrations.

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I will use 10cm of magnesium ribbon for each separate reaction, and I will rub each piece with sandpaper beforehand, in order to remove magnesium oxide which will have formed on the surface. This amount is an excess, because I do not want the concentration of the magnesium to change significantly during the reaction. Although this would still be a problem with the amount of magnesium I am using if I was letting the reaction carry on for a longer time, but since I am only interested in the initial rate of each reaction, the change in concentration of the ...

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