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My aim is to make Epsom salts at 4 different speeds, by choosing one factor/variable which will change the speed, and to predict and measure the yield of Epsom salts using the mole.

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Introduction

Chemistry Coursework Aim: * To make Epsom salts at 4 different speeds, by choosing one factor/variable which will change the speed. * To predict and measure the yield of Epsom salts using the mole. * To plan a safe affective method, to measure the speed and record useful data. What is Epsom Salts? Epsom salts with the common name magnesium sulphate heptahydrate, MgSO 4 �7H 2 O, a water-soluble bitter-tasting compound that occurs as white or colourless needle-shaped crystals. It was first prepared from the waters of mineral springs at Epsom, England; it also occurs as the mineral epsomite. Epsom salts is used medicinally as a purgative; it is also used in leather tanning, mordant dyeing, and as filler in cotton goods and paper. Rate of reactions The effect of concentration A reaction can be made to go faster or slower by changing the concentration of a reactant. Using the reaction between magnesium and excess hydrochloric acid is repeated twice (A and B). Everything is kept the same each time, except the concentration of the acid. What happens in each reaction? * The curve of reaction A is steeper than B. Meaning A is faster than B. * In A the reaction lasted 60 seconds, whereas it lasted 120 seconds in B. * Both produced 60cm3 of hydrogen. In A the hydrogen was produced in 60 seconds, so the average rate was 1cm3 of hydrogen per second. In B it was produced in 120seconds so the average was 0.5cm3 of hydrogen per second. The average rate in A was twice the average rate in B. A reaction goes faster when the concentration of a reactant is increased. (Complete Chemistry - Rose Marie Gallagher, Paul Ingram) The effect of temperature A reaction can also be made to go faster or slower by changing the temperature of a reactant. An experiment using dilute hydrochloric acid is mixed with sodium thiosulphate solution, a fine yellow precipitate of sulphur forms. ...read more.

Middle

One person from the group will be in charge of measuring out the reactants and someone else is timing. This is reducing the risk of different readings due to different measurements and reaction times. Although it is mostly inevitable. Fair Test To make the experiment a fair test the amount and concentration of the acid must be kept the same and be measured by the same equipment and person to keep the accuracy the same, 40ml and a concentration of 0.25M. The amount of Magnesium must also be kept the same, as the only variable is the surface area of the magnesium. The accuracies of the measuring devices should also be kept the same to stop major differences in the amount used. Diagram Pilot Run Results Type of Magnesium Amount of Mg (g) Amount of H2S04 Time (seconds) 30 60 90 120 150 180 210 240 Ribbon 0.51 40 30 66 90 114 130 148 160 172 Turnings 0.52 39 30 58 78 88 100 110 118 126 Powder 0.5 40 42 80 102 110 112 116 118 120 The above pilot runs were done to check that the amount of magnesium and Sulphuric acid were right to get a product and for the reaction to be at the right speed for us to be able to accurately measure the readings. We also had to use some pilot runs testing with concentration to use: Concentration Type of Magnesium Amount of Mg (g) Amount of H2S04 Time (seconds) 30 60 90 120 150 180 210 240 We decided to use a concentration of 0.25M, with 40ml of Sulphuric acid and 0.5g of Magnesium. Amendments made For the real experiment we decided to use smaller differences between the time intervals. This was because we found with the faster reactions the reaction was slowing dramatically towards the end and accurate readings weren't taken. We will also take 3 readings of each surface area, then take an average. This will mean many anomalous results should be taken out. ...read more.

Conclusion

2 ml to be accounted for. * We also noticed with come of the magnesium floated on the top of the acid. This means only the under side could be attacked by the acid. This would halve the surface area and dramatically decrease the speed. * Some of the Epson salts were left in the tray and not measured this could mean we had a higher yield than stated. * On two experiments we were required to make up our own concentrations. This may have meant it was not completely accurate, increasing or decreasing the rate of reaction. To combat these problems we could: * Use a special upside down measuring tube, which is more accurate. * Use a taller, and thinner, more accurate measuring cylinder to measure out the sulphuric acid to make it more correct. * Measure the temperature throughout the experiment, so this can be taken into account when we evaluate the experiment. * To use a method which meant that the measurement was taken when it was meant to be. This may mean taking a count down to when it should be taken so the person taking the result could have time to read it accurately. Improved method To improve my result I got from this experiment I would: * Use a heated bath where the acid would be kept so that the temperature of the room will not make a difference to the rate of reaction. The collision theory, means that as temperature increases so does the amount of successful collision so the rate of reaction. * Use a pipette when measuring out the acid, this will mean you can attain the exact amount needed. Using the same balance to measure the magnesium should also keep the amounts the same. * Use one concentration of Acid made from the same set. This would mean keeping this acid set aside so all the same one is used. * Using a burette to measure the amount of hydrogen produced, these are more accurate and can be read off easily. Nichola Vowles 11G Page 1 of 13 ...read more.

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