The Relationship between Concentration of Hydrochloric Acid and the Rate of Reaction - Lab Report Example

Aim This experiment aimed at investigating the relationship between concentration of hydrochloric acid and the rate of reaction. Introduction The experiment reaction is represented by the following chemical equation Mg(s) + 2HCl (aq) --> MgCl2 (aq) + H2(g). The level of concentration of HCL is proportional to its volume while the rate of reaction is proportional to reciprocal of time (1/time). When there is a faster reaction, the time required to raise the same volume of hydrogen gas is reduced. Thus when the volume of HCL used is changed and different reaction time for collecting a certain amount of gas being obtained, it is possible to calculate and do analysis for relationship between concentration of HCL solution and rate of reaction between hydraulic acid and magnesium. Hypothesis The number of successful collisions per unit time is the determinant factor of the rate of reaction. Collision theory is made use of in the determination of the relationship between the level of concentration of reactants and the rate at which collision takes place. According to collision theory, the conditions for reaction are that the two particles taking part in the reaction must 1. Must be involved in a collision with each other 2. There should be enough energy of overcoming the activation energy of the reaction 3. Collision need to take place with favourable geometric alignment, which will bring the reactive parts of the molecules in contact. In the present experiment, the increasing concentration of hydrochloric acid will increase the chances of there being a collision between the hydrochloric acid particles and the magnesium particles in the time period required to consumer a certain amount of magnesium. If there is an increase in the total number of collisions, there would be also an increase in the number of successful collisions, even when the ration of successful collisions remaining constant. Thus the hypothesis for the experiment is that the high concentration of hydrochloric acid would translate to high rate of reaction being witnessed between magnesium and hydrochloric acid. Materials and apparatus Magnesium ribbon 3M hydrochloric acid solution Distilled water One 10 ml measuring cylinder( ±0.05mL ) One 25 ml measuring cylinder( ±0.05mL ) One Stopwatch( ±0.01s ) One Clamp stand One Glass trough One 0-100⁰C Temperature probe( ±0.5⁰C ) One Test tube with a rubber plug and a delivery tube One Digital weighing balance( ±0.001g ) A pair of scissors One transparent beakers with separate droppers Set-up diagram Procedures 1. No more than 100 ml solution was taken from the 3M HCl solution bottle into a dry clean beaker with a dry pipette and the beaker was labelled with a sticker indicating “3M HCl solution”. 2. Appropriate amount of water was taken in the other beaker with a clean pipette. 3. The Magnesium ribbon was cleaned using a sand paper to remove oxides coating its surface to make it have a metallic lustre. 4. 18 pieces of Magnesium strips of equal lengths were cut from the fleshly cleaned Magnesium ribbon using scissors. Their weights were checked by the same digital weighing balance and were then recut so as to make all of them to be 0.030 gram each. 5. The magnesium pieces were then wrapped with paper towel to reduce the chance of them being re-oxidised. 6. 10 ml of 3M hydrochloric acid was transferred from the labelled beaker into a clean dry 10 ml measuring cylinder and then poured into a clean dry test tube. 7. a gas delivery system was prepared including water bath with the following being observed. The water trough almost filled with water. the 25ml measuring cylinder was filled with water and the open end was covered with the palm making sure no bubbles of air remained. The measuring cylinder was Inverted and the open end placed under the surface of the water in the trough. The hand was then removed. The measuring cylinder was clamped into position. a 0-100⁰C temperature probe was put into the water tough and temperature of distilled water was recorded when the reading stopped changing. 8. The stopwatch was reset and one piece of Magnesium strip picked and dropped into the test tube with solution in it and the rubber stopper plugged immediately, while another team member started the stopwatch as soon as the Magnesium piece got in touch with the HCl solution. 9. The 25 ml measuring cylinder was watched horizontally and the stopwatch was stopped running the moment when the gas collected reached 10 ml in the measuring cylinder. The reaction duration was recorded on a data sheet in seconds with accuracy of 2 decimal places. 10. All the chemicals were discarded; the 10 ml measuring cylinder and test tube were thoroughly rinsed for next procedures. 11. Procedures 6-10 were repeated for three times for the same concentration. 12. Procedures 6-11 were repeated for 5 different concentrations of the HCl solution, diluting as in Table 3. Observations i. Before: Magnesium is silver/white with metallic lustre, and hydrochloric acid is clear and colourless solution. ii. During : Odourless and colourless gas which has density less than that of water and weak solubility is produced. The rate of bubbling for each reaction decreases as the reaction goes on. Solution remains clear and colourless during the reaction, whereas the Mg strip gradually becomes smaller and smaller. iii. After: Since when we stop timing our reaction after 10 ml gas is collected, Magnesium is not used up in all trials and the reaction is still going on by the evidence of bubbling at surface of Mg strip. We did not do any observations after the reaction. Data Table 11. Raw data of repeated measurements of duration of reaction between HCl solution and Magnesium strip for various concentrations of HCl solution. Volume of 3M HCl, VHCl ± 0.05/ml Volume of H2O, VH2O ± 0.05/ml Concentration of HCl, c/M Mass of Mg, m ±0.001/g Temperature, T ± 0.5/⁰C Time, t ± 0.2/s Trial 1 Trial 2 Trial 3 10.00 0 3.0 0.030 20.5 4.2 5.7 5.6 8.00 2 2.4 0.030 20.5 6.0 6.5 6.0 6.00 4 1.8 0.030 20.5 8.9 9.3 9.9 4.00 6 1.2 0.030 20.2 24.1 20.0 24.8 2.00 7 0.6 0.030 20.5 126.0 142.7 148.9 3.00 8 0.9 0.030 20.5 36.6 39.9 37.0 Uncertainty In volume: half the smallest scale of division of 10 ml measuring cylinder (±0.5 ml) In mass: smallest scale of digital weighing balance (±0.001g) In temperature: half the smallest scale of division of the 0-100⁰C temperature probe (± 0.5⁰C) In time: Half the smallest scale of digital stopwatch (±0.005s) Human reaction time (±0.2s) Since human reaction times are much slower than the uncertainty in stopwatch itself (±0.005s), ±0.2s should be used as the uncertainty in a time measured with a stopwatch. Table 2.Processed data of average time and rate for the reaction between HCl and Mg Concentration, c /M Percentage error in concentration Average time, t ± 0.2/s Percentage error in time (1/time),(1/t) /s-1 Percentage error in time 3.0 ±0.5% 5.2 ±3.8% 0.19 ±3.8% 2.4 ±3.1% 6.2 ±3.2% 0.16 ±3.2% 1.8 ±2.1% 9.4 ±2.1% 0.11 ±2.1% 1.2 ±2.1% 22.9 ±0.9% 0.0442 ±0.9% 0.6 ±3.1% 139.2 ±0.1% 0.0262 ±0.1% 0.9 ±2.4% 37.8 ±0.5% 0.006840 ±0.5% Table 3. Processed data of log of rate and log of volume of HCl for the reaction between HCl and Mg Figure 2. Graph of reaction rate V.S. concentration of HCl for the reaction between HCl and Mg Figure 3.graph of log (1/time) V.S. log (volume of HCl) for the reaction between HCl and Mg Conclusion The data was found to be supporting the hypothesis as in figure 2, it was observed that there was upward curving, a clear indicator that reaction rate was increasing with increasing HCL concentration. In figure 3 a quantified relationship between reaction rate and concentration of HCL has been given. the data is seen to exhibit linear regression line which has a gradient of 2.05 an indication that the order of concentration is 2.05 as far as the rate law for reaction between HCL and Mg. this value can be seen being very close to the expected theoretical value and the small difference can be well be accounted for by uncertainty in apparatus. This means that an increase in the concentration of hydraulic acid brings about an increased rate of reaction in a power 2 manner and thus validating the hypothesis. Evaluation The completion of experiments was under the same lab conditions with the temperature of the water bath being kept constant. The team members were assigned individual tasks and this ensured that uncertainty emanating from different operating techniques did not arise. The raw data results were seen to be reliable with the reaction times which were obtained in the tree trials for certain concentration showing only difference as shown in Table 1. There are some random errors that were exhibited in the experiment as indicated by the outliers but the general trend is an increase. With same solution not being used in the entire experiment, the reaction times are likely to be faster or slower than is expected and this is likely to bring about random errors. The possibility of having various levels of oxidation of the Mg piece for each set up could also bring about the variations. And also, as illustrated in table 3 apparatus uncertainty is relatively large and this may affect the precision of the experiment a great extent. Improvements The following are possible improvement that can be made 1. There should replacement of magnesium strip by specific amount of powder magnesium to avoid struggle with the cleanness of magnesium pieces, and this is likely to show clearer reaction times. 2. There is need for fresh hydrochloric acid for dilution each time so as to avoid change in concentration 3. In the process of experiment design apparatus with smaller scales are to be used or there should be use of reactants of high quantities so as to bring down apparatus uncertainty and to increase precision in the experiment. 4. There is need for more experiments to be done for lower concentrations so as to have more extreme difference of the reaction and to better confirm the hypothesis. More repetitive trials are to be undertaken for each concentration as to reduce random errors. References http://www.rsc.org/learn-chemistry/resource/res00000449/the-effect-of-concentration-on-reaction-rate?cmpid=CMP00000519 http://www.science.uwaterloo.ca/~cchieh/cact/c123/coneffec.html http://www.alkaseltzer.com/as/student_experiment3.html Read More