The Effect of Acid Concentration on the Rate of Reaction

The Effect of Acid Concentration on the Rate of Reaction
Introduction: We are going to investigate the effect of Acid Concentration on the Rate of Chemical Reaction. We are going to use the combination of Hydrochloric Acid and Calcium Carbonate as the reactants: Calcium Carbonate + Hydrochloric Acid Calcium Chloride + Water + Carbon Dioxide Prediction I predict that the greater the concentration of acid the greater the rate of chemical reaction i.e. the rate of reaction will be directly proportional to the concentration of acid. This means that if I were to double the concentration of acid the rate of reaction would also double, halving the time taken. In order to generate a more accurate picture I have constructed a series of graphs highlighting my above statements. I have used a relative scale, following my prediction, in order to calculate the rate and therefore time taken. Concentration (Molar) Rate Time Taken 2.0 5 0.2 1.6 4 0.25 1.2 3 [image] 0.8 2 0.5 0.4 1 1 [image] This graph shows the concept of how the greater the acid concentration the greater the rate of reaction.
The idea being that with a concentration of 0 moles the rate would be infinity, comparatively by increasing the concentration of acid, the more instantaneous the reaction becomes. [image] This graph represents the relationship that exists between acid concentration and rate; by increasing the acid concentration the rate is increasing as well. The straight line indicates the direct relationship; double the acid concentration you double the rate of reaction. Justification The Collision theory justifies the prediction of increased acid concentration causing increased rate of reaction by relating to the concept of proportional molecular content; i.e. if there are more acid molecules they are more likely to collide with those of the Calcium Carbonate molecules: Acid Molecule Calcium Carbonate Collision [image] The diagrams above illustrate the greater likelihood of a collision in 2.0 molar concentrations due to the higher concentration of acid. We can also back this up with some maths: If we take the reactions to have taken place in 100ml of water (different to that of my forthcoming practical) we can see that the ratio of acid molecules to calcium carbonate molecules is smallest in the 2.0 molar reactions: 2.0 Molar Reaction 0.4 Molar Reaction [image] [image] 1.6 Molar 0.8 Molar [image] [image] If we now look at the rate of reaction we can see that is also justified by the aid of maths: Rate Time Taken 5 [image] 0.2 4 [image] 0.25 3 [image] [image] 2 [image] 0.5 1 [image] 1 The rate was calculated using the formula of : [image] [image]This enabled us to predict the time taken for the experiment [image]And there fore the graph of Time Taken vs. Concentration: Just before we began to start our coursework we carried out a pilot test in order to aid us in determining what concentrations of acid we were to use. Not only did this aid us in working out quantities for our reaction but also in adding further evidence to our prediction. We found that the higher the concentration of acid the larger the rate of reaction, something which we had expected. Another interesting observation was the decrease in effervescence as the acid concentration lessened- showing yet again a decrease in the rate of reaction. Strategy The strategy I will use to determine the rate of chemical reaction will be to measure how fast the gas will be produced;[image]. I will do this by timing the amount of time it takes to fill a gas syringe (to a set amount of 50cm³) from the reaction of Calcium Carbonate and Hydrochloric Acid. In doing so we will control other factors: Controlled Variables Independent Variables Dependant Variables Temperature Acid Concentration Time Taken Volume of Acid Volume of Gas produced Mass of Calcium Carbonate Surface Area pf Calcium Carbonate Light Intensity Use of a Catalyst Pressure This will then produce a picture representing the relationship between acid concentration and rate of reaction. Safety As with any experiment safety is a key issue to which we must address before starting the experiment. Not only will it prevent harm occurring but it will also aid the fluidity to which we carryout our experiment. Below are a few important rules that we will adhere to when performing our experiment: ? Wear Safety Goggles and Lab Coats at all times during the experiment ? No running within the laboratory ? Prevent contact with chemicals ? do not taste or place them in your mouth! ? Wash your hands after handling chemicals Method and Apparatus Apparatus: A 200cm³ Conical Flask ? allows ample room for volume of reaction A 100cm³ Measuring Cylinder ? enables me to dilute the acid concentration precisely. A Clamp and Boss ? in order to suspend the syringe A Retort Stand ? in order to suspend the syringe A Delivery Tube ? transfer the gas produced to the syringe without any leaks (which would effect the experiment) A Stopwatch ? time the time taken for the reaction to produce 50cm³ of gas A Bung ? prevent any loss of carbon dioxide produced from the experiment (which would effect the experiment) A Gas Syringe ? enables me to measure accurately the quantities of gas produced. An Electronic Balance ? to weigh precisely the amount of calcium carbonate 1.5g of Calcium Carbonate (per experiment) Hydrochloric Acid Distilled Water ? allowing me to vary acid concentration [image][image] Gas Syringe [image] Delivery Tube [image][image] [image]Bung [image][image][image] Retort Stand Conical Flask [image] [image] [image] My first step will be to set up the apparatus as shown; suspending the gas syringe from the retort stand, connecting it to the conical flask via the delivery tube. Once the apparatus is setup I will weigh 1.5g of Calcium Carbonate, adding it to the conical flask. Next I will measure 100ml (using the measuring Cylinder) of Hydrochloric Acid - correct to the right concentration: Acid Molar Hydrochloric Acid (ml) (%) Distilled Water * (ml) (%) 2.0 100 100 0 0 1.6 80 80 20 20 1.2 60 60 40 40 0.8 40 40 60 60 0.4 20 20 80 80 *N.B. We will be using Distilled Water to dilute the acid in the above ratio?s Using the electronic balance weigh 1.5g of calcium carbonate and add it to the conical flask. The slickness of the next phase will be fundamental to achieving correct and fair results. The Acid, composed in the correct concentration, will be added to the conical flask, in which already resides the calcium carbonate, sealing the reaction chamber with the bung.. At this same time, the stop clock must be started. I have chosen to measure the production of gas to the quantity of 50cm³; therefore as the gas passes through the delivery tube, we will stop and record the timer when the syringe contains 50cm³ of carbon dioxide. The experiment will then be reset in order for us to repeat the experiment 3 or 4 times an acid concentration ? in order to rule out anomalies. Fair Test The creation of a fair test is fundamental to the object of Science; otherwise the results will lead to the wrong conclusions whether this is during a simple experiment, like ours, or the attempted creation of nuclear fission. During our experiment we will try to produce accurate results. To do this we have taken certain precautions in order to save guard us from any erroneous results. ? Firstly we will be using powered calcium carbonate. This will allow us to keep the surface area during each experiment to an equal acceptance; i.e enabling us to have a single variable ? acid concentration. The regularity of surface are is paramount for creating a fair test as a substance with a larger surface area will be able to come into contact with more of the acid or vice se versa (as shown by the diagram). The powdered calcium carbonate will prevent this problem as the powdered format will give a regular surface area. [image] [image] [image][image] ? The room temperature, although not precisely maintained, will be inconsequential to our experiment. The temperature of the experiment could affect the rate of reaction if there was an increase in temperature the particles would gain more kinetic energy causing them to move faster increasing the chances of collision ? speeding up the reaction. ? Pressure will remain the same. An increase in pressure could cause an increase in rate as in effectively condenses the space available for the reaction to take place in, creating a larger chance of collision. The diagram illustrates the concept, showing you how the area in which the molecules can move is reduced thus creating a large chance of collision. [image] ? The volume of acid will be kept at the same level ? 100ml ? as different quantities of reactant will change the rate of reaction; higher ratio of acid quantity to quantity of Calcium Carbonate ? would improve the likelihood of collision. ? In relation to the previous factor is therefore obvious that we should also keep the quantity of Calcium Carbonate at the same level for the same reason of quantity ratios- would improve the likelihood of collision. ? Light Intensity is another factor we will attempt to keep the same, although the room conditions should not fluctuate sufficiently as to affect our results. ? In order to highlight any irregularities within our experiment we will repeat the experiment multiple times per concentration. ? Stirring the reaction is another factor that would increase the rate of reaction and subsequently will be controlled (i.e. will not occur). Stirring the reaction would increase the chance of collision due to the increased movement of the molecules (also sometimes the increased availability of surface area): [image] ? Further problems could be posed from the apparatus; the gas syringe for instance; if a previous experiment had affected the fluidity at which it moves, sudden jolts in movement would be detrimental in creating inaccurate results. Other possible problems could come from leaks within the apparatus. Unfortunately there is not a lot we can do about preventing this bar observing any impediments or problems in relation to our apparatus. These factors were kept in mind when we began to plan our experiment - during our pilot test. We realised that we needed a concentration that would not be so quick as to be affected by our swiftness (or not as the problem would be) at starting the stop clock etc. or indeed so slow as to prevent us from collecting more than one set of results. Our results from our pilot test: Combination Tested ? Quantities Conclusion Acid (ml) Calcium Carbonate (g) Gas collected (cm³) 50 0.5 50 Is it reacting? 50 1.5 50 Too Slow 50 2.0 50 Too Slow 100 2.0 50 Too Fast 100 1.0 50 Slow 100 1.5 50 Chosen measurement We concluded that it would be best to settle with a 100ml of acid as it would ease the process of using percentages and further calculations; we therefore changed quantities in order to fit around this 100ml idea. Factors The factors affecting our experiment are shown below. In order to perform a fair test certain key factors must be kept constant while only one factor must change ? the independent variable. How we intend to control these factors is shown below: Controlled Variables Independent Variables Dependant Variables Temperature Acid Concentration Time Taken Volume of Acid Volume of Gas produced Mass of Calcium Carbonate Surface Area pf Calcium Carbonate Light Intensity Use of a Catalyst Pressure After we had planned our experiment out thoughts turned as to how we would present our results. We constructed a design for our table of results: Acid Concentration 1 Time (s) 2 Time (s) 3 Time (s) 4 Time (s) 100% (2.0 molar) 80% (1.6 molar) 60% (1.2 molar) 40% (0.8 molar) 20% (0.4 molar) Acid Concentration Average Time (s) Observations 100% (2.0 molar) 80% (1.6 molar) 60% (1.2 molar) 40% (0.8 molar) 20% (0.4 molar) Results Acid Concentration 1 Time (s) 2 Time (s) 3 Time (s) 4 Time (s) 100% (2.0 molar) 11.0 8.0 9.0 8.0 80% (1.6 molar) 12.0 10.0 Anon: 21.0 9.0 13.0 60% (1.2 molar) 16.0 Anon: 23.4 14.0 15.0 9.0 40% (0.8 molar) 21.0 24.0 26.0 25.0 20% (0.4 molar) 50.0 43.0 Anon: 60.0 47.0 48.0 Acid Concentration Average Time (s) Observations 100% (2.0 molar) 9.0 Effervescence occurred when the Calcium Carbonate was added to the acid solution. The rate of effervescence decreased as the experiment went on, also the gas syringe moved slower as the experiment went on. At the end of the lower acid concentration experiments there was a white solid which stuck to the bottom of the conical flask. 80% (1.6 molar) 11.0 60% (1.2 molar) 16.0 40% (0.8 molar) 24.0 20% (0.4 molar) 47.0 [image] [image] Conclusion The Graph Acid Concentration vs. Time Taken shows a curve, reflecting the graph of our prediction. It shows that as acid concentration doubles the time taken halves. The gradient of the graph is changing (decreasing as the x axis unit increases) the reason for this is because as acid concentration doubles the time taken will halve, this is justified because there are more acid molecules available to react with the Calcium carbonate creating a large chance of collision. There is no intercept for the graph and logically there never will be, as time can never equal zero and a reaction with no acid at all for example would mean no reaction and therefore the reaction time will be infinite. The Graph for Rate vs. Acid Concentration follows the same pattern as that of my prediction. It shows that as acid concentration increases the rate of reaction increases. The constant gradient (of [image]) shows that rate and acid concentration are directly proportional to one another, proving the idea that if you double the acid concentration you will double the rate of reaction. There is only one intercept on the graph which is 0.04 on the x axis and -0.002 on the y axis. Theoretically this point should be the origin as when there are no acid molecules within the reaction, then the rate of reaction will be zero (is only one reactant). The reason why my results do not begin at the origin is due to a slight slip during my experiment. Within my graph there are no anomalies. This is due to me spotting them at the end of the said experiment, and repeating that particular concentration in order to rule out the anomaly. This is represented on the graph with the strong correlation surrounding the line of best fit. Acid Concentration (M) Time Taken (s) Rate [image] 2.0 9 [image] 1.6 11 [image] 1.2 16 0.0625 0.8 24 [image] 0.4 47 0.0213 Ratio of Time Taken (s) Ratio of Rate [image] 9:11:16:24:47 => 0.2:0.2[image]:0.3[image]:0.5[image]:1.0[image] 5:4.5:3.13:2.08:1.07 Predicted Ratio of Reaction Rate Actual Ratio of Reaction Rate 5:4:3:2:1 5:4.5:3.13:2.08:1.07 Predicted Ratio of Time Taken Actual Ratio of Time Taken 0.2:0.25: [image]:0.5:1 0.2:0.2[image]:0.3[image]:0.5[image]:1.0[image] The above tables are there to illustrate the exactness between predicted results and actual results. This proves the idea that increased acid concentration does increase rate of reaction. Evaluation Experiment Problems: Significant problems for me during the experiment came with the sealing of the reaction. It was difficult (exaggerated with the reactions of higher acid concentrations) to place the bung on the conical flask, with all the acid in, without the loss of carbon dioxide. I encountered this same problem during the preliminary experiments and concluded that it would be plausible to delay the sealing of the reaction by a time (of 1 second) in order to regulate the loss of carbon dioxide throughout the experiment. Having set this measure in place, problems still arose leading to erroneous results. However I found that the main problem was that not all the acid could be added straight away meaning some reacted whilst the rest was being added. This would mean that at points at the beginning of the reaction the ratio of calcium carbonate and hydrochloric acid would not be as predicted, causing different chances of collision. This remained an unsolved problem for the duration of the experiment but seems not to have affected my results too much. Another minor problem came in the adding of the calcium carbonate. I choose to weigh the calcium carbonate on a piece of paper, and upon pouring the powder into the flask, grains were lost. However the levels were so insignificant they did not affect the results of my experiment noticeably. So where the answers accurate? In most cases the concept of delaying the application of the bung to the conical flask prevented any erroneous results however there were cases where this occurred creating anomalous results however they were fortunate to be so obvious that they were spotted and the experiment repeated again. The problem with adding all of the calcium carbonate was, as I pointed out unsolved. However as it remained relatively equal per experiment it has not effected my results greatly (although of course without repeating the project with improved methods I would never know for sure), such that I have results that match those of my prediction. The problem of not adding the full 1.5g of calcium carbonate turned out to be so slight as to not have effected the experiment in any noticeable way (although I will never know for certain unless I repeat the experiment with improved methods). If I were to repeat the experiment I would look at different options concerning the apparatus. I would look to improve the delivery mechanism; attempting to prevent any delays in adding the calcium carbonate (and applying the bung). It may also be an idea to look at using a different material/apparatus to weigh the calcium carbonate, attempting to prevent any remnants of calcium carbonate being omitted from the reaction ? this may need preliminary testing in order to ascertain the correct material/apparatus. In total I took 19 readings but made 3 mistakes. This presents a relatively high success rate, as: This shows me that in my experiment I had an 84.2% success rate. This method can also be applied to the individual experiments, looking at how the preciseness of the apparatus could present errors: The margin for error, looking at the table above, shows quite a staggering possible % error. Interestingly enough it also shows the %error to decrease as the acid concentration also decreased. However this is not an exact art, only a possible error. This is reflected in our results matching so closely to those of our prediction. Other non-quantifiable sources of error could be: Temperature ? The experiment was carried out at room temperature which was not controlled precisely. This poses a possible cause for errors within our results however the effect of temperature would have to vary greater that 2 or 3ºc in order to affect the rate of reaction. Pressure ? This was again not measured but as the conditions were atmospheric which is not prone to large fluctuations, we can assume this didn?t change my results by any considerable means. Light Intensity ? The light intensity again was not measured neither was it able to be controlled precisely. However as the light intensity barely makes a difference to the reaction rate, in respect to the fluctuations experienced, this is almost a dismissible margin of error. Reliability The repetition of the tests did and would narrow the margin of error giving more accurate a conclusion and theoretically the more you repeated the experiment the more accurate your average would be however it is not feasible and indeed necessary to exceed say 5 tests per concentration for as you can see I carried out the experiment only 4 times per concentration and still recorded extremely exact results. It is therefore that I feel that my reliability problems arose not with strategy but with apparatus. As I have already stated one of my main problems arose in sealing the experiment with all its reactants whilst preventing any loss of reaction products. Of course any loss in reaction products would effect you results considerably. I feel that if the experiment were to be repeated to a higher level of accuracy I would feel it prudent to devise an improved delivery system, enabling the reaction products to meet at the same time, whilst preventing the loss of any carbon dioxide. On top of this I would look at further nullifying of human error i.e. in the timing of the experiment. In the modern age of technology it could possible be important to introduce a computer data logging system. This would enable the time taken for the gas to be collected to be precisely calculated from the start of the experiment, with out the problems of the experimenter having to manually gage the start and finish of the experiment. The use of a computer would also increase the exactness of the timer, i.e. to points of a second. Of course this could be introduced without a data logging system. Along this same apparatus theme, the use of a gas syringe although accurate, prevented me from recording larger volumes of gas, this would further support the idea of using a computer data-logging system, as an improved collection vessel could provide further insight into the relationship between acid concentration and rate of reaction. As we strive to further the specifics of the experiment we could also look to control the controlled factors to a more significant level. E.g. Temperature; of course under the ?classroom? conditions that we practised under, I was never going to be able to keep it a precisely constant level however this could be controlled, along with light intensity and pressure, in an improved facility, enabling to look at the problems these fluctuations did pose, if any. As a summary, I feel that my results fit firmly with my own scientific knowledge, providing no strange abnormalities. The results fit the graphs and ratios like that of the prediction proving to me that my conclusion is firm and correct. Limitations The obvious limitations came with the ability to truly control the controlled variables (although this seems not to have affected the results). On top of this the pattern given by the results on the graph would extend to higher acid concentrations and lower acid concentrations, something which I was not able to test. This could provide further evidence, even problems with my conclusion. It also may be an idea to look at other variables and their relationship with acid concentration on the affect of rate of reaction. For example, it may be that the affect of a increased acid concentration might be greater at a greater temperature or pressure. This I feel is an important limitation, although I remain satisfied with the truth of my conclusion/ Further Work As I have mentioned above I feel it a limitation to the simplicity of our experiment. I feel it would have been of importance in surmising the affect of acid concentration and rates of reaction to have the knowledge of how other factors would affect this e.g. varying other variables or the amount of gas evolved. In respect of a greater collection of gas, I feel that this would be important as I predict that the rate of reaction would decrease within a reaction, something which is not able to be accounted for in my simple reaction. This concept is backed up by f observations of a decrease in effervescence as the experiment continued, however this is not quantifiable, therefore not firm evidence. The further varying of other variables (as I have already mentioned) I feel would be of importance as it would show where the effect of acid concentration on the rate of reaction stands in comparison to others; looking at how some work best in conjunction with others or not ? a case for further study. As we noted earlier certain factors were not able to be controlled precisely. Therefore given further time it would be relevant to test these factors, controlled specifically, in order to see by just how much they affected our experiments, if at all.

The Effect of Acid Concentration on the Rate of Reaction 7.1 of 10 on the basis of 2774 Review.