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What factors affect the rate of reaction between magnesium ribbon and hydrochloric acid? This chemistry coursework requires an investigation to see how long it takes for magnesium ribbon to be eaten away by hydrochloric acid. Before starting the investigation, I decided to do some research about magnesium and hydrochloric acid. Magnesium is a light, shiny grey metallic element, symbol Mg, atomic number 12, found in group two in the periodic table. It is quite reactive giving vigorous reactions towards acids. It is one of the alkaline earth metals, and the lightest of the commonly used metals. It is used in alloys, flash photography, flares, fireworks and flash bulbs because it burns vigorously in air with a bright white light. Magnesium reacts with steam to release hydrogen and it also burns in carbon dioxide gas. Hydrochloric acid, HCl, is a solution of hydrogen chloride (a colourless acidic gas) in water. The concentrated acid is about 35% hydrogen chloride and is corrosive. The acid is a typical strong, monobasic acid forming only one series of salts, the chlorides. Like most acids, it releases hydrogen ions when it is added to water and certain metals, and has a pH of less than 7. Hydrochloric acid is a common laboratory acid. Before looking at the factors that can alter the rate of reaction, we must consider what happens when a reaction take place. First of all, the particles of the reacting substances must collide with each other and, secondly, they need a certain amount of energy to break down the bonds of the particles and form new ones. This energy is called the activation energy or Ea. If a collision between particles can produce sufficient energy (i.e. if they collide fast enough and in the right direction) a reaction will take place. Not all collisions will result in a reaction. The investigation could be done using one variable and therefore have a set of results which were related in some way. The variables that could be used are: 1. Concentration 2. Particle size/surface area 3. Pressure (for reactions involving gas) 4. Temperature 5. Light 6. Presence of a catalyst. These variables can be used because: 1. The more concentrated the reactants, the greater the rate of reaction will be. This is because increasing the concentration of the reactants increases the number of collisions between particles and, therefore, increases the rate of reaction. 2. When one of the reactants is a solid, the reaction must take place on thesurface area of the solid. By breaking up the solid into smaller pieces, the surface area is increased, giving a greater area of collisions to take place and so causing an increase in the rate of reaction. 3. When one or more of the reactants are gases an increase in pressure can lead to an increased rate of reaction. The increase in pressure forces the particles closer together. This causes more collisions and increases the rate of reaction. 4. An increase in temperature produces an increase in the rate of reaction. A rise of 10º C approximately doubles the rate of reaction. When a mixture of substances is heated, the particles move faster. This has two effects. Since the particles are moving faster they will travel greater distance in a given time and so will be involved in more collisions. Also, because the particles are moving faster a larger proportion of the collisions will exceed the activation energy and so the rate of reaction increases. 5. The rates of some reactions are increased by exposure to light.
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