Doron Hershkorn 10ww science coursework
Chemistry
“The effect of varying the concentration of the reaction between magnesium and hydrochloric acid”.
Aim: The aim of this investigation is to find out the effect of concentration of acid, in the reaction between dilute hydrochloric acid and magnesium ribbon. The rate of a chemical reaction is a measure of how fast the reaction takes place. It is important to remember that a rapid reaction is completed in a short period of time. Some reactions are very fast, For example (the formation of silver chloride precipitate when silver nitrate and hydrochloric acid solutions are mixed).In this investigation we will test different concentrations of acid reacting with magnesium.
Prediction: I predict that as the concentration of the hydrochloric acid increases, the time taken for the magnesium to disappear decreases. I predict that when the concentration of the hydrochloric acid doubles, the rate of the reaction doubles.
Linking prediction to theory, Reaction rate and concentration: The collision theory describes how the rate of reaction increase (the time taken for the magnesium ribbon to disappear when it is reacted with hydrochloric acid) when the concentration of hydrochloric acid increases. The theory states that if the more concentrated the reactants, the greater the number of collisions between particles increase. This also explains why the greatest rate of reaction is usually as soon as the reactants have been mixed, As the reaction continues, the concentration of the reacting substances decrease and so does the rate of reaction. We must consider what happens when a reaction takes place. First of all the particles of the reacting substances must collide with each other, and secondly a fixed amount of energy called activation energy must be reached if the reaction is to take place. If the particles can produce the right amount of energy (if they collide fast enough and in the right direction) a reaction will take place. The reaction is speeded up if the number of collisions is increased. In this investigation we must consider the topic of variables. Clearly, the time taken for the magnesium to disappear when it is placed in different concentrations of hydrochloric acid is related in some way. The higher the concentration of hydrochloric acid you use, the less time it takes for the magnesium ribbon to disappear and so the rate reaction increases. The concentration of hydrochloric acid you use is the independent variable because it will vary, and the time taken for the rate of reaction to take place (i.e. the magnesium ribbon to disappear) is the dependant variable because it depends upon the concentration of hydrochloric acid. Other variables throughout the investigation, which will vary are the volume of water used, and the volume of hydrochloric acid. The variables which will remain unchanged are the temperature (room temperature) will stay the same in order for it to be a fair test, because if the temperature changes it will effect the rate of reaction between the reactants, either by speeding it up if the temperature rises because the particles move faster and travel a greater distance in a given time and so will be involved in more collisions. Or the temperature may slow the reaction down due to particles moving slower. The amount of magnesium used will stay the same (10cm long), so that it is a fair test. The time it takes for the magnesium to disappear will be measured accurately using a stop clock as soon as the hydrochloric acid is poured into beaker with the magnesium in it. This way most results will be accurate. It is important to keep the reactants separate while setting up the apparatus so that the starting time of the reaction will be measured accurately. Factors which may not be easy to control are, how well the solution is mixed when it is diluted, to get the correct concentration. This factor is quite important because it determines exactly what the concentration of the solution is each time it is mixed , if the stirring factor is not carefully controlled it could lead to inaccurate results if the concentration of the acid solution is not what we calculated it to be. During a chemical reaction the particles have to collide with enough energy to first break the bonds and then to form the new bonds and the rearranged electrons, so it’s safe to say that some of the particles don’t have enough energy to react when they collide. A change in concentration is a change in the number of particles in a given volume. If we increase the volume the particles are more crowded so they collide more often.
