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I aim to investigate the rate and mechanisms of the reactions between magnesium and acids.

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Introduction

PLANNING Aim I aim to investigate the rate and mechanisms of the reactions between magnesium and acids. Introduction The reactions I will investigate are nitric acid with magnesium, and sulphuric acid with magnesium. I will vary the concentration of nitric and sulphuric acid in separate experiments, and I will vary temperature in order to study what effect these variables have on the rate of reaction. The mass of magnesium used will remain constant. My experience in chemistry suggests that the rate will increase with both concentration of acid and temperature, the exact relationships will be investigated. The variation of rate can be described by the rate equation, specific for each reaction. The rate equation must be found by experiment rather than predicted by theory, it takes the form: Rate = k[A]x[B]y where the square brackets indicate the concentration of the substance indicated inside them, the x and y indicate a power that this concentration is raised to and k is the rate coefficient. The rate coefficient is constant at a constant temperature, and its variation with temperature is described by the Arrhenius equation: k=Ae(-E/RT) where E is the activation enthalpy, R is the molar gas constant, T is the temperature and A is a constant. ...read more.

Middle

Note that the sodium hydroxide was added rapidly as soon as the time period had elapsed. This whole process was then repeated with different concentrations of nitric acid, all other variables are constant. The nitric acid was diluted from its original 2M by the table below. The entire process was then repeated with sulphuric acid in place of nitric acid. Then the whole experiment was repeated at 50�C. This was achieved by placing all reactants; acid, sodium hydroxide and magnesium in separate boiling tubes and submersing them in a water bath set at 50�C. There they were left to heat for five minutes, and then the acid added to the magnesium and the boiling tube placed back in the water bath. The titration was performed as before. Dilution Table Start with 2M nitric or sulphuric acid, depending on experiment. Always make up to 20cm3. Water used is distilled water. 2 M 20cm3 acid 1 M 10cm3 acid, 10cm3 water 1.75 M 17.5cm3 acid, 2.5cm3 water 0.75 M 7.5cm3 acid, 12.5cm3 water 1.5 M 15cm3 acid, 5cm3 water 0.5 M 5cm3 acid, 15cm3 water 1.25 M 12.5cm3 acid, 7.5cm3 water 0.25 M 2.5cm3 acid, 17.5cm3 water Risk Assessment Clearly I will be dealing with strong concentrated acids and alkalis and so care must be taken not to allow contact with skin or eyes. ...read more.

Conclusion

Fewer, in fact half, as many moles of sulphuric acid will react with the same amount of magnesium as nitric acid, due to the ratios of the reactions below: Mg + 2HNO3 ==> Mg(NO3)2 +H2 Mg + H2SO4 ==> MgSO4 +H2 HNO3 + NaOH ==> NaNO3 + H2O H2SO4 +2NaOH ==> Na2SO4 +2H2O EVALUATION Sources of Error The 10cm3 measuring cylinders used to measure out the volumes of acid and base were accurate to �0.1cm3. The burette used in the titration was accurate to �0.05 cm3. There is human error involved in judging the end-point of the titration, though I chose methyl red as my indicator as it gives a very clear colour change and was very careful in my method it is possible that I did not measure the exact end-point. It is also likely that such an error would not be systematic and so could affect the results randomly. Improvements If I were to perform this investigation again with unlimited resources, I would first use larger quantities of all reactants in order to reduce possible error and to make conclusions firmer. I would investigate a wider range of acids, acid concentrations and temperatures in order to draw firmer conclusions about the trends and relationships I have identified. 1 Page ...read more.

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