Courseworks

A Medicinal Problem

This is an investigation to try to produce Magnesium Sulphate (MgSO4) in an efficient way as an anti – inflammatory agent for medicinal purposes. The company producing Magnesium Sulphate has received a very large order due as soon as possible. One way of producing Magnesium Sulphate is to add Magnesium (Mg) to Sulphuric Acid (H2SO4). A chemical reaction takes place because the Magnesium is higher up in the reactivity series than the Hydrogen (reactive part of any acid) and therefore replaces the Hydrogen to form Magnesium Sulphate.Scientific Knowledge:Part of scientific knowledge is the collision theory which firstly states that for particles to react they must first collide. Secondly for reactants to react they require a minimum amount of energy. The rate of reaction is related to the collision theory since that for there even to be any rate of reaction the collision theory has to take place.Strong acids have pH’s of 1 – 2 and react a lot more violently than weak acids of pH 5 – 6. The pH of acids change around one main factor the quantity of Hydrogen ions in the solution of any acid. In a strong acid nearly all the molecules form ions while in weaker acids fewer Hydrogen molecules form ions.When Magnesium reacts with Sulphuric Acid the acid molecules which split up and Hydrogen gas dispersesWord equation:Magnesium + Sulphuric Acid Magnesium Sulphate + HydrogenSymbol equation:Mg (s) + H2SO4 (aq) MgSO4 (aq) + H2 (g)All factors that affect the rate of reaction in this experiment are the concentration of the acid, temperature of which the reaction is performed, surface area of the Magnesium ribbon and the presence or absence of a catalyst. The concentration matters as the higher the concentration of the acid the time taken for the reaction to be completed decreases as more Hydrogen ions can break up the Magnesium atoms in a shorter amount of time. The more successful collisions there are , the less time required to complete the reaction. This idea also explains why the reaction between Magnesium and Sulphuric acid slows down as time goes on (as shown on sketch graph on following page).Concentration of the Sulphuric Acid:Low concentrationglass beaker At a low concentration there arefewer hydrogen ions to react withthe Magnesium so collisions areHydrogen ions in far between. This means theSulphuric Acid reaction will take longer.MagnesiumHigh concentrationAt a high concentration there is more Hydrogen Hydrogen ions in ions present so the Sulphuric Acid collisions are closer together. The more collisions happen more often so greater chance of reaction.MagnesiumThis sketch graph is the rate of reaction compared to the time it takes to complete the experiment of changing Magnesium and Sulphuric Acid into Magnesium Sulphate and Hydrogen.TIME(s)ConcentrationTemperature of which the experiment is carried out:Low temperatureThe Hydrogen ions have less energy at a low Hydrogen ions in temperature so don’t Sulphuric Acid collide as strongly therefore Hydrogen ions don’t always have enough energy to complete reaction.MagnesiumHigh temperatureThe Hydrogen ions have more energy so they Hydrogen ions in move faster and collide Sulphuric Acid more often and more vigorously. This leds to a higher percentage of success.MagnesiumSurface Area of Magnesium:Small surface areaA large lumps of solid has a small surface area. Hydrogen ions in This will slow down the Sulphuric Acid rate of reaction because the Hydrogen ions can only react with the outside layer of the Magnesium ribbon.MagnesiumLarge surface areaSmall lumps of the same mass of magnesium have a large surface area. This Hydrogen ions in will speed up the rate of Sulphuric Acid reaction because the Hydrogen ions have more magnesium atoms on the surface to react with.MagnesiumThe Presence or Absence of a CatalystA particular phenomenon associated with the rates of chemical reactions that is of great theoretical and practical interest is catalysis. This phenomenon is the acceleration of chemical reactions by substances which are not consumed in the reaction themselves – these have become known as catalysts. The term catalyst came from the Greek words Kata – meaning down and lyein – meaning loosen. Catalysts speed up reactions, they do this by lowering the minimum temperature required for a specific reaction to be completed. Catalysts can be solid, liquids or gases. All living things both plant and animals contain many biological catalysts. These biological catalysts are called enzymes. Catalysts have become extremely important for business’s now as they help produce chemicals on a large scale quickly for very little extra. The graphs below show the same reaction, one with a catalyst and one without.After deliberating over all the factors that change the rate of reaction I have come to the decision that the factor that I will investigate will be the concentration of the Sulphuric Acid. I decided to investigate the concentration of the Sulphuric Acid. I made this choice mainly on how easy it is to change the concentration of Sulphuric Acid simply by adding water this means that it will also be easy to repeat the experiment exactly for the number of times required. I didn’t chose temperature simply because it would be almost impossible to repeat the experiment exactly as the first time had been done. Likewise I didn’t choose the Surface area of the Magnesium as this would be even harder that the temperature as the surface area is next to impossible to work out as a human and I don’t have a computerized tool of such nature at my disposal. Whether or not a catalyst was present was not what I chose because Catalysts are not as easy to measure as the temperature at which the experiment is being carried out.Now the variables have to be identified and placed into the correct categories. The independent variable (what is going to be investigated by being change during the experiment) is the concentration of the Sulphuric Acid. The dependent variable (what is going to be measured) is the time taken for each reaction to take place. The controlled variables ( what needs to be kept constant for a fair test to be achieved) one is the temperature at which the reactions are carried out at, another is the mass of magnesium ribbon used and finally the apparatus used throughout the experiment.There is a prediction required for this experiment and what I predict is; that as the concentration of the Sulphuric Acid increases the time taken for the reaction to be completed decreases. To justify this prediction you have to scan back to the factors which effect the rate of the reaction, there it says at a higher concentration of an Acid there is more Hydrogen ions amiable to react with the Magnesium atoms than at a lower concentration. This can be summed up simply in that at a higher concentration there is more Hydrogen ions present so more collisions occur therefore reaction takes less time.Apparatus and Chemicals required:Quantity Apparatus/ChemicalRequired2 50cm3 burette1 100cm3 beaker200cm3 Sulphuric Acid at 100g/dm326cm Magnesium1 Stop clock1 Small ball of steel wool1 Small square piece of paper (about 5×5 cm) 1 Retort stand1 Boss1 Burette clamp1 30cm ruler1 Pair of scissorsMethod:1: Set up the apparatus as shown on the diagram on the next page for the reaction between Magnesium and Sulphuric Acid.word equation:Magnesium + Sulphuric Acid Magnesium Sulphate + HydrogenSymbol equation:Mg (s) + H2SO4 (aq) MgSO4 (aq) + H2 (g)2: Using the burettes measure out the exact amount of Sulphuric Acid and/or water required for each experiment into the 100cm3 beaker.3: Measure out 2cm of Magnesium ribbon with a ruler and cut using scissors.4: Drop the 2cm of Magnesium into the dilute Sulphuric Acid and start clock as Magnesium ribbon touches the Acid.5: When the reaction is complete stop the clock and record the time in the results table (the reaction ends when the Magnesium stops moving violently about on the surface of Sulphuric Acid).6: When all of the required reactions have been completed fill in remainder of the results table.I intend to change my independent variable (concentration of Sulphuric Acid) by changing the volume of water present. For the first reaction I will use 20cm3 of water and 5 cm3 of Sulphuric Acid. I will then decrease the volume of water by 5cm3 each time until no water remains. At the same time I intend to increase the volume of Sulphuric Acid by 5cm3 until no water dilutes the acid. The measurement taken for this experiment is the time taken for the reaction to take place. The time will be measured in the unit of seconds. From the answer in of time, in seconds, the rate of reaction will be worked out. To ensure that all the measurements are correct each reaction will be repeated and results compared if the results aren’t similar the reaction is repeated until two similar results are obtained. When these two similar results are obtained they are then added together and divided by two to get the mean (average). The ranges for all of the chemicals used in this experiment are as follows. The range for the water is from 20cm3 – 0cm3. The range for the Sulphuric Acid is from 5cm3 – 25cm3. There is no range for the Magnesium ribbon as it is one of the controlled variables so is fixed to the distance of 2cm. I will make my investigation fair by keeping the temperature constant throughout all of the reactions, keeping the length of magnesium strip constant and by keeping the volume of dilute Sulphuric Acid constant.Safety:The safety required for this experiment is very important because Sulphuric Acid is corrosive to the skin and is also harmful to the human body. In carrying out this experiment the pupil should handle the acid with great care as it is corrosive and may damage the human skin even in a dilute form. The pupil should also wear goggles to protect their eyes from the fizzing of the acid when reacting with the Magnesium. This experiment should carry the following safety symbols:Strategy for dealing with results:I believe that a table would be necessary to show the results clearly with the aid of a graph. There is a possible results table for this experiment below:The graph that I intend to draw to show my results in their final form is a line graph I chose this because it is the easiest to work with and shows the results very clearly. This is the type of graph that I would expect to obtain:RATESOFREACTIONTIME (S)To work out the concentration of the dilute Sulphuric Acid, 25 is divided by the volume of dilute Sulphuric Acid. The number 25 is chosen simply because the total volume of liquid (Sulphuric Acid + water) at the start of each reaction is 25cm3. The mean (average) time can be calculated by taking the two similar times and adding them together and dividing by 2. The rate is then calculated by dividing 1000 by the mean time (seconds) taken for the reactions to be completed.I will ensure that the results achieved from this experiment are precise and reliable by repeating them for as many times as necessary, until similar results are obtained.Obtaining Evidence:The results that I got when I did the experiment are as follows:There were no changes made to my original plan.My results did produce some inconsistancies because I had to repeat four of them a third time to ensure an accurate average is obtained. Even after repeating the results a fourth time there was more time available for me if it had been required.

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