An Investigation into the factors affecting the rate of reaction between magnesium and hydrochloric acid

Volume = 0.00416 * 2

Volume = 0.0083dm3

Volume = 8.3cm3

It was decided to use an excess of hydrochloric acid to ensure all the magnesium reacted, therefore 10cm3 of acid was used in the pilot experiment. At room temperature 10cm3 of hydrochloric acid was added to 0.1g of magnesium and the gas was collected (see fig 1). The volume of gas produced was measured every 15 seconds. It was found that the reaction was too rapid to be effectively measured, therefore 10cm3 of water was added to halve the concentration of the acid.

* Investigation Experiment

I am going to investigate how temperature affects the rate of reaction between magnesium and hydrochloric acid. The procedure for the experiment is as follows;

* Using a measuring cylinder, measure 10cm3 of water and pour it into the side arm tube.

* Measure 10cm3 of hydrochloric acid (1 mol/ dm3) and add it to the water.

* Place the side arm tube in a water bath at 20OC, set up the apparatus below.

* Measure 10.9 cm of magnesium ribbon and check on the balance that it weighs 0.1g.

* Coil the ribbon around a pencil and then drop it into the side arm tube and quickly put a bung on the side arm tube (this must be done quickly to prevent gas escaping).

* Every 15 seconds measure the volume of gas produced until less than 1cm3 of gas is produced every 15 seconds.

* Repeat experiment two more times (for accuracy) and record all results in a table.

* Repeat the experiment for temperatures of 30 OC, 40 OC, 50 OC and 60 OC

It is important that only the temperature is changed since this is what is being investigated.

Method

* Apparatus

I have chosen to use a 10cm3 measuring cylinder to measure the volumes of substances used since it is more accurate than a pipette. I will use an electronic water bath for maintaining the mixture at a temperature since the temperature is more accurate than a water bath above a Bunsen burner.

A 100cm3 gas syringe should be appropriately accurate for measuring the gas produced since it is accurate to 1cm3 of gas. I will use a three figure balance to measure the mass of magnesium to be used since it is vital that as close to 0.1g of magnesium is used as possible.

* Variables

I have chosen to repeat the experiment 3 times because it therefore allows me to calculate an average rate of reaction. This will ensure that there are no abnormal results and it will increase accuracy. I have decided to start readings at 20OC and increase by 10OC each time until 60OC is reached, since it will allow me to see the increase in rate of reaction and 5 results should be enough to identify any trends.

* Rates of Reaction

Increasing the temperature increases the speed of the particles. The faster the particles move, the greater the number of collisions, and therefore the rate of the reaction increases. A 10OC rise in temperature almost doubles the rate of most reactions.

Chemical reactions take place by chance. Particles need to collide with enough velocity so that they react. As the temperature is increased the particles move faster since they have more energy. This means that they are colliding more often and more of the collisions have enough velocity to cause a reaction. Since there are more collisions the chemical reaction takes place faster.

Analysing Evidence

First three graphs were drawn (one for each time the whole experiment was carried out). So that the graphs did not become over crowded the curves were drawn on separate pieces of see through OHP film and overlaid each graph. Note: They have been attached all overlaid their appropriate graph but should be viewed one at a time overlaid the appropriate graph. A tangent was drawn at the beginning of each curve and its gradient calculated, the gradients are shown in the table below.

The average gradient was calculated and then the gradients plotted on a graph. As the temperature increases so does the rate of reaction. Increasing the temperature increases the speed of the particles. The faster the particles move, the greater the number of collisions, and therefore the rate of the reaction increases.

Chemical reactions take place by chance. Particles need to collide with enough velocity so that they react. As the temperature is increased the particles move faster since they have more energy. This means that they are colliding more often and more of the collisions have enough velocity to cause a reaction. Since there are more collisions the chemical reaction takes place faster.

In my design I predicted that as the temperature increased the rate of reaction would increase. I predicted that for every 10OC increase in temperature the rate of reaction would double. I was correct that as the temperature increases so does the rate of reaction however the rate of reaction does not double for every 10 OC increase in temperature although it is a linear relationship.

Evaluating Evidence

I believe that the experiment was successful but some of the results were unexpected/unreliable. The lines on the graphs for 20OC and 30OC cross, this doesn't affect my results since I am only concerned with the initial rate or reaction but it was unexpected. In graph 3 the rate of reaction for 60OC is lower than that of 50OC - this result is anomalous and has been ignored in this investigation.

I believe that the experiment was designed well but there were a few problems. Although the initial rate of reaction (which is what I am concerned with in this investigation) seemed to fit a trend, the rate of reaction curves of some temperatures on the graphs crossed. This could have been because some of the magnesium had corroded forming a magnesium oxide layer which would have affected the rate of reaction.

Other factor which could have given me unreliable results could have been that the gas syringes were wet causing them to jam and so not giving correct results or that the bung was not placed on the top of the side arm tube fast enough which allowed gas to escape. I conducted all three experiments for each temperature at the same time to save time. An error in my graphs (plotting, drawing curves or calculating gradients) could have also affected the calculated rates of reaction.

To improve the experiment I would find a way of attaching and releasing the magnesium inside the side arm tube above the acid (with a bung at the top of the side arm tube) so that the magnesium could be dropped into the acid without any gas being lost.

Additional work, which could be carried out, is to repeat the experiment using, a wider range of temperatures. The investigation could also be extended to investigate other factors affecting the rate of reaction such as catalysts, concentration of the acid or particle size of the magnesium.