The control variables (the variables kept the same): The other variables, which we need to keep constant, are:
- The volume of H2SO4 being added to each reaction. This will be kept constant throughout the investigation by accurately measuring 10mL of H2SO4 solution for each trial in a measuring cylinder. This is vital for a fair test as varying it would mean that reaction rate is not only being altered by the effects of varying concentration but also that of volume.
- The same climatic conditions present around the experiment. The climatic conditions, in particular temperature will remain the same throughout the experiment to prevent natural processes and disturbance from impacting the experiment. These will be kept the same as no windows will be opened or closed and the air conditioning will not change in temperature or switch on/off after the experiment has started. Temperature, itself, possesses the ability to change the rate of reaction and hence, it is vital to keep it controlled and constant so that the results only reflect the impact of varying concentration.
- The same mass of Magnesium (Mg) ribbon to be reacted with the H2SO4 solution (0.05g). The laboratory technician will keep this constant beforehand, as they will provide us with the pre-cut ribbons for our experiment. This mass has been chosen, as it is a sufficient for a distinct reaction to be witnessed in a suitable period of time.
- Preventing cross contamination from occurring between trials and different concentrations of H2SO4 solution. To prevent cross contamination, we will clean the two measuring cylinders and test tube with distilled water before each trial, ensuring that no residue from previous trials remain in either of the instruments.
- The target volume of H2 gas to be produced by the reaction in each trial- 20mL. This will be kept constant by first determining the ideal amount and then clearing calculating on the measuring cylinder 20mL less than the water level inside it so that it is clear during the trial when to stop the stopwatch. Pre-determining a target volume is vital for us to be able to effectively compare and form a relationship between the concentrations of H2SO4 and time taken to produce the same amount of hydrogen gas.
- The same person handling the stopwatch during the experiment. Identifying one group member to handle and use the stopwatch before the experiment and then ensuring that he only handles it during each trial will control this variable. It is vital to reduce the impact human error and keep the experiment as accurate as possible.
ALL EQUIPMENT IS TO BE KEPT CONSTANT TROUGHT THE EXPERIMENT TO OBTAIN CONSISTENCY
- 1x Test Tube
- 1x Delivery Tube
- 1x Rubber Stopper
- 2x 50mL Measuring Cylinders
- 1x Plastic Container
- 1x Retort Stand and Clamp Set
- 1x Laptop
- 1x Desk
- 1x Stopwatch
- 2x Distilled Water Bottles
- 12x 0.05g Magnesium Ribbons
- 2500mL of water (H2O)
- 30mL of each H2SO4 Solution (0.5M, 1M, 1.5M & 2M concentrations)
Setup & Plan:
- Collect all necessary equipment from the equipment table- all equipment should be in one tray.
- Setup the retort stand and clamp on a stable desk. The clamp should be fixed approximately half way up the stand.
- Open up Photo Booth or a similar video/image-capturing program on a laptop so that evidence of the experiment and setup can be visually shown.
- Place the plastic, ice-cream container on the desk adjacent to the retort stand and fill it 2/3 of the way up with water from the tap.
- Fill one of the measuring cylinders with 100mL of water and place inverted into plastic container. Ensure to cover top with hand until fully submerged into container so to prevent leakage of water.
- Take delivery tube (with rubber stopper attached to one end) and place through inverted cylinder (side without rubber stopper). This should not be difficult, as water pressure of plastic container will keep 100mL in measuring cylinder whilst tube is being inserted.
- Measure out 10mL of the 0.5M, H2SO4 solution in second measuring cylinder and pour into large test tube.
- (Start of trial) Place one strip of magnesium ribbon (0.05g) into large test tube and immediately cover top of tube with rubber stopper end of delivery tube. Ensure that it is firmly attached and air tight.
As soon as reaction begins with H2SO4 solution already in test tube, start timing the rate of reaction using the stopwatch.
- Measure and record the time it takes for the water level in the inverted measuring cylinder to decrease by 20mL. This will indicate that it has been replaced by 20mL of hydrogen gas.
- Reset the experiment by rinsing the measuring cylinders and test tube with distilled water; refill the inverted measuring cylinder with 100mL of water and carefully place back into plastic container with delivery tube passing through it.
- Measure another 10mL of 0.5M, H2SO4 solution in second measuring cylinder and pour into test tube.
- Repeat steps 8 and 9 again, adding the 0.05g, Mg ribbon to the reaction in the test tube, cap of the test tube with the rubber stopper end of the delivery tube and time until 20mL of H2 gas has been produced in inverted measuring cylinder.
- Rinse all equipment with distilled water once trial 2 is completed and measure out another 10mL of 0.5M, H2SO4 solution. Reset experiment like in step 10 and pour measured solution into clean test tube.
- Begin trial 3 and repeat steps 8 and 10 again. If the previous two trials yielded similar results, trial 3 should also be of similar time length. If at the end of three trials, there is an anomaly within them, it may be required to complete a fourth trial to clean up data.
- Repeat steps 7-14 again with the 1M, 1.5M and 2M H2SO4 solutions. The process is the same with the only variable changing being the concentration of H2SO4.
- Once finished, record gathered results onto laptop and return all equipment. Ensure to clean all test tubes and measuring cylinders with distilled water before returning.
- Write up report, ensuring to include a marked-scattered graph and results table with averages established for each concentration of H2SO4 tested. If required, process the data to achieve a desired relationship between the two variables.
*NOTE: Capture pictures throughout experiment with the laptop and remember to write down all observations.
Results Table: Time Taken To Produce 20mL of Hydrogen Gas (sec) From a Reaction Between Magnesium Metal (Mg) and Different Concentrations (M) of Sulfuric Acid (H2SO4)
Graph: I think the best kind of graph to use to display these results would be to create a marked line graph with a line of best fit (Trendline):
Throughout the investigation we collected and gathered observations using our five senses, with the sound of the reaction, the sight of the reaction and the heat of test tube all extending our knowledge and understanding of this phenomenon. The fizzing sound that the reaction was creating was because of the chemical bonding taking place between the metal and acid. The fizzing was also visible to the eye, as when the magnesium was added to the reaction in the test tube, it combined with the H2SO4 and produced bubbles. Furthermore, particles of higher concentration H2SO4 collided and reacted with the magnesium particles to produce magnesium sulfate and hydrogen gas at a quicker rate. The heat developed in the test tube also varied significantly with more concentrated solutions radiating warmer temperatures due to higher levels of friction and energy in the reaction.
The relationship achieved in the above graph between the two variables is of a quadratic, inverse relationship with no modifications made to the data. To achieve a linear relationship between the independent and dependent variable, me must process and modify the results. This is outlined in the table below:
Graph: I think the best kind of graph to use to display the modified results would be to create a marked line graph with a line of best fit (Trendline):
Our results show a wide range of relationships between the data. For instance, the shape of our initial graph shows an inverse, quadratic relationship between the concentration of H2SO4 and time required to produce 20mL of H2 gas from its reaction with Mg metal. The polynomial trend line displays this relationship in the first, raw data graph with an equation of y = 60x2 - 254x + 350, creating a “minimum” parabola. From here, we were able to deduce a set of modified results- taking into account two specific rules required to develop a linear relationship from an existing inverse relationship (represented in the table above).
Hence, the second graph provides us with a linear relationship between the two variables in that it possesses a straight line with the equation: y = x + 350. The value of the modified gradient is one, signifying that for every additional 1/0.5M rise in concentration of H2SO4; an equivalent ratio of decrease is experienced for the time taken to produce 20mL of H2 gas. In relation to the research question, our data collected clearly shows that the rate of reaction between an acid and metal substances is quickened by an increase in concentration of the acid substance. The data looks fairly reliable as there are no anomalies or outlier’s present- with the data plotted on the marked scattered graph all being located along the trend line which intersects each mark near-perfectly, suggesting the data’s accuracy with the rule. However, there was slight variation between the three trials of each concentration, suggesting slight variation between the conditions for each trial.
The results gathered are sufficient and clearly show a distinct relationship detailing that the stronger the concentration of the H2SO4 solution, the quicker/faster its rate of reaction with magnesium metal, proving my hypothesis valid as I had hypothesized that “as the concentration of the H2SO4 solution increases/strengthens (measured in molarity mass), it will correspond to an increased/quicker rate of reaction with Mg metal”. Evidence from the data collected shows that the strongest concentration of H2SO4 (2M) only required an average of 80secs to produce 20mL of H2 gas, where as the most dilute solution trialed (0.5M) required an average of 240secs- more than any other trialed concentration.
There is enough evidence to show that unless the data is modified and processed, a linear relationship is not formed between the two variables, indicating that there is no direct proportionality between the increase in concentration and time taken to produce 20mL of hydrogen gas. This occurs because the reaction between H2SO4 and Mg is an exothermic reaction so a small amount of energy has been released/transferred out of the experiment as the reaction progressed.
Our experiment went quite well and we were able to collect all the necessary readings required. We encountered very few problems during the course of the experiment and were able to conduct three trials for each H2SO4 concentration, thus improving the reliability of our data and deeming the experiment fair and valid. We had a sufficient sample size of four different concentrations at equal intervals of 0.5M-adequate for this experiment and allowing for a conclusive relationship to be established. The extensive range of data collected through the conduction of three trials for each concentration of H2SO4 allowed us to obtain an accurate trend line and formulate justifiable conclusions. Furthermore, our results for each concentration of H2SO4 were similar each trial with no major outliers in the data, implying that our control of the constant variables was successful, all data was precise and accurate averages were deemed. Analyzing our results, we were able to achieve the phenomena (affects of concentration on the rate of reaction between a metal and acid substance) we were interested in and hence were able to answer our research question in the affirmative that the concentration of an acid (in this Sulfuric acid) does effect its reaction of rate with magnesium metal, with the relationship being that an increase in concentration (molar mass) equates to an increased/quicker rate of reaction- evidenced by the time taken to produce 20mL of hydrogen gas.
Our method was fairly clear, concise and allowed us collect our data in a fairly orderly way, doing so for most tests. It allowed us to complete the experiment with accuracy excluding the effects of the one, major problem (mentioned above) that were inevitable based on the way the experiment was conducted. Although our method and experimental plan were quite accurate, easy to understand and allowed us to achieve our target of determining a distinct and logical relationship, there are still many improvements that could be made to it to improve the validity of our results and further experiments could be carried out to extend this investigation. These include:
- Completely eliminating human impact in the experiment by a valve of some sort to add the magnesium ribbons to the reaction in the test tube with the rubber stopper already firmly attached to the test tube. This will mean that the slight deviation in data is not experienced.
- Using a larger sample size- (i.e. 8-10 different concentrations of H2SO4) so that the relationship gathered can be further strengthened and backed up by more evidence.
- Investigate whether changing the concentration of H2SO4 has an impact on the time it takes for the reaction to reach equilibrium (the end of the reaction) and form a relationship from there.
- Use different types of acids and metals with different properties to investigate if the rate of reaction is similar to that between Sulfuric acid and magnesium or it is quicker/slower.
- Trialing different factors that affect the rate of reaction such as temperature or agitation and evaluating their influence compared to that of altering the concentration.