To make the experiment the experiment a fair test and reliable test, the following variables will, throughout the experiments, remain unchanged or controlled:
- The temperature (room temperature) will stay the same. Because changes (increase or decrease) in temperature will alter the rate of reaction between reactant either by speeding it up or slowing it down.
- The amount of magnesium used in all experiment remained the same (2cm long) to make it a fair test. The time it takes for the magnesium to disappear will be measured accurately in seconds by starting using the stopwatch as soon as the magnesium strip is placed into the beaker with the hydrochloric acid in it. This will make the results more accurate.
- The reactants (mg and hcl acid) will be kept apart or separate while setting up the apparatus so that the starting time of the reaction and of its end could be measured accurately.
PREDICTION
My prediction is that as the concentration of hydrochloric acid increases, the rate of reaction increases (i.e. it takes less time for the magnesium strip to completely disappear). I also predict that when the concentration of hydrochloric acid doubles the rate of the reaction doubles. This is so because the theory of chemical reaction states that the rate of reaction increases as the concentration of hcl acid increases: in concentrated acid there are more acid particles crowded together in the solution i.e. there is more chance of successful acid particle collision taking place with magnesium atoms (more collisions speed up the reaction); while in diluted acid the number of acid particles are not that many and their chance of colliding with magnesium atom is not much. The more concentrated the reactants, the greater the number of collisions between their particles increase. In other words, the fastest rate of reactions usually happens immediately when the reactants are mixed, as they are both at their highest concentrations. But as the reaction continues, the concentrations of reactants decrease and so does the rate of reaction.
METHOD
In this experiment we are going to measure the time it takes for magnesium strip metal to disappear at each level of concentration using a stopwatch and using our eyes (visual) to determine when the magnesium disappeared the apparatus and ingredients listed below would be used in this experiments:
Ingredients Apparatus
Water One beaker
Hydrochloric acid (hcl) One cylinder
Magnesium strip (mg) Stopwatch
Safety Goggles
When the apparatus and ingredients was being set up the chemical reactants i.e. hydrochloric acid and magnesium strip were kept separate so that the starting time of the reaction could be measured (in seconds) more accurately. Once the apparatus were set up with ingredients ready we began the test: we made sure to wear safety goggles and through out the experiment to protect our eyes from the harmful acid. Also, when any harmful acid spilled on our hands we had to wash it out immediately.
- First we added the magnesium strip into the beaker containing the concentrated (100%) hydrochloric acid and simultaneously started the stopwatch. We closely observed the reaction between the magnesium strip and the acid until the strip disappeared completely and the clock stopped. The time is noted in the table.
- Next we lowered the concentration of acid by 10 ml and added 10ml of water into the beaker. Then the magnesium strip placed in the beaker with the solution again we started the stopwatch at exactly the same time as the strip was placed in the beaker. Closely watching the reaction we stopped the clock until magnesium strip disappeared when we stopped the stopwatch and measured the time taken for the magnesium strip to completely disappear using the stopwatch. Time again noted in the table.
- Then the concentration of the acid was lowered by the same amount (10 ml) and diluted with 20 ml of water was poured into the beaker. The magnesium strip was placed into the beaker, simultaneously starting the stopwatch. We followed the reaction visually to determine the exact time the magnesium strip disappeared to stop the stopwatch and measure the time taken for the magnesium to disappear completely, which is noted in the table.
- Then the concentration of the acid is again lowered by 10 ml and diluted with 30 ml of water was poured into the beaker and the magnesium strip was placed in the solution at which exact time the clock started. We kept our eyes on the experiments so that we can determine the time the magnesium disappeared to stop the watch and measure the time taken for magnesium to disappear using the stopwatch and we noted it on the table.
- Again with the concentration of the acid lowered by the same amount and diluted with 40 ml of water the whole process is repeated as above. All the measured times were regarded in the table below. It should be noted that we made sure that we started the stopwatch, at exactly the same time as the magnesium strip is placed in the solution to measure the start of the reaction to the finish of the reaction where the same care was taken to stop the stop watch at the point the magnesium disappeared, end of reaction. We also made sure that the amount of magnesium used remained the same in all the experiments (2 cm long). We repeated the experiment three times to get a fair test by showing that all results are accurate. All the results are clearly shown on the table below and their average is calculated. However any results that largely disagree with the other two results (I.e. about 10 seconds or more out) it is regarded as anomalous result i.e. the remaining two are averaged.
The table of results
Percentage Amounts Time taken for mg Average predicted
concentra- of water to Strip to disappear result time time in
-tion % dilute acid EXP (1) EXP(2) EXP(3) (secs) (secs)
100 0 12.68 25.68 16.49 15 30
80 10 21.94 26.35 24.54 24 60
60 20 40.56 37.95 41.79 40 120
40 30 97 98 104 100 240
20 40 821 650 708 680 480
N.B.
The underlined measurements in the above table are not included in the calculations of the averaged as they are considered anomalous.
RESULT
Both the results of the experiments in the table and their drawn line graph show that it takes less time for magnesium strip to fully react or disappear in concentrated acid than in diluted acid. This confirms or agrees well with my prediction and with theory of collisions which states that in concentrated acid there are many acid particles, which are very close to each other (or crowded together) in the solution and Therefore there is very good chance of many particle collision with magnesium atoms these collisions are what makes reactions speed up.
In diluted acid the number of acids particles are scarce with little chance of colliding with magnesium particles and therefore the reaction takes more time to complete or the magnesium to disappear.
Plotted line graphs
- Line graphs of results of experiments to demonstrate the relationship between acid concentration and the rate of reaction. A line graph of averaged experimental results is drawn with time in seconds on the vertical axis and the percentages of concentration on the horizontal axis. The graph has curved shape and becomes almost flat at higher percentages of concentration levels. The graph shows clearly that as the concentration of the acid decreases, the time taken for the magnesium strip to disappear continually increases. For instance at 100% concentration the time taken for mg to disappear is just 15 secs but as the percentage of the concentration decreases from 80% to 60% the time taken for the reaction to finish almost doubles from 25 secs to 40 secs. This agrees quite well with my prediction as the concentration increases so does the rate of reaction.
Line graph
- The theory of chemical reaction states that if the concentration of the acid halves then the time taken for the reaction to take place will double. Now if, for instance, it is fully react when the concentration is 20% is 480 secs then the time taken for the reaction to finish when concentration is 40% is 240 secs. Similarly at 60%, 80% and 100% concentration, the times for the reactions to finish will be 120 secs, 60 secs and 30 secs respectively. A line graph based on this ideal data was plotted on the same graph on which the average experiment data is drawn. It can be seen that the similarity of the two graphs is quite remarkable: both graphs have curved shapes and both graphs become flat towards higher concentration levels. The fact that the graph of experiments result is so similar to the predicted line graph is fairly accurate. Also the graphs show that less time taken for the magnesium strip to disappear in concentrated acid than dilute acid (at 100% it takes 15 secs and at 60% it takes 40 secs).
ANALYSIS
From the table of experiments results it can be concluded that fastest rate of reaction (time it takes for the magnesium strip to disappear) takes place when the concentration of the acid is at its highest (100%): it only took 15 seconds on the average for magnesium strip to disappear completely. But as the concentration level of acid decreases due to addition of water to it, the time taken for the magnesium strip to disappear continually increases from 100% at 80% the time for the reaction to finish is double 25 of 100%for instance the time taken for the magnesium as the concentration decrease from 60% to 40% to fully react or disappear when the concentration is 60% is 40 secs while 40% concentration time as 100% secs and finally 20%concentration the reaction time is almost 680 secs.
CONCLUSION
From the results of the experiments it can be concluded that at the highest concentration level of the acid, the rate reaction is fastest it only takes the magnesium strip to disappear in 15 secs and the average. But the time is more than doubled as the concentration is halved i.e. at 60% when the concentration of the acid doubles. The rate of reaction doubles 40%-15% because in the concentrated acid solution the acid particles are closer together. The closeness of particles helps them to collide more often, and this frequent particle collision increase the chance of a reaction between the magnesium strip and the hydrochloric acid. Also the great number of particles in the concentrated acid solutions would increase the chance that they would hit the magnesium so the reaction rate would increase. When the concentration of the acid is very low the time taken for the magnesium to react increases because in diluted acid there are not many acid particles moving in the solution and therefore their chance to collide with magnesium atoms to react is very low. In the lower 40%-20% concentration the time increases from ……to … ….
EVALUATION
The experiment were done in a fair manner and the result are reasonably accurate because:
- The stopwatch always was started and stopped at the right times (start to end) during the duration of the reactions of the reaction.
- Great care was exercised to determine when the reaction had finished.
- The same amount of magnesium-2cm in length.
- The experiment was repeated three times and the measurement (reaction time in secs) was averaged to increase its accuracy. And exactly the same quantities of acid and water used in all experiments however it should be admitted that the visual determination of the end of the reaction could lead to incorrect time measurement as the attention of the experiment may lapse at a times some times measurements which greatly differed from others and disregarded in average calculations may be due to this fact. Also the hydrogen bubbles being given off by the reaction may stay be entrapped around the magnesium reducing its surface area and therefore hinder the acid to properly react. This would affect the measured reaction time or result.
The experiment will be greatly improved if the magnesium strip is powdered. This increases its surface area, which makes more magnesium atoms exposed. So there is a greater chance of successful particle collision that quicker the rate reaction. Secondly the use of warm acid solution or catalyst would have made the reaction between acid and magnesium faster lastly measuring simultaneously the rate of production of hydrogen bubbles would have given control factor data to compare with the experiment result when both data are drawn in line graphs.
