Purpose: The purpose of this laboratory experiment is to determine the mole to mole ratio of reactants in a chemical reactants, when the formulas of the products is unknown.
Data Tables:
Experiment
1 2 3 4 5 6 7 8 9 10 11 |
Ratio: mL of NaClO to mL of Na2SO3
0:50 5:45 10:40 15:35 20:30 25:25 30:20 35:15 40:10 45:5 50:0 |
Temperature
*C 22.2 24.9 28.2 30.5 33.1 35.2 35.9 32.1 28.0 24.1 22.2 |
Change in Temperature
*C 0 2.7 6 8.3 10.9 13 13.7 9.9 5.8 1.9 0 |
Graph of Data: Change in Temperature versus Reactant Volume Ratios
Conclusion:
After completeing the experiment, it was determined that the best ratio of NaClO to Na2SO3 is 28.5mL to 22.5mL. This was found by graphing the various ratios of each compound compared to the change of temperature, as completed in the experiment. These values were then used to find the number of moles, using the molarity value given in the procedures for the lab. From the number of moles, the whole number coefficients that form the ratio were found, by dividing by the smallest number of moles, which was Na2SO3. After multiplying these quotiens by three to create whole numbers, the mole to mole ratio was found to be 4NaClO and 3Na2SO3, a ratio of 4 to 3. This is an accurate ratio, because it falls between the two highest temperatures on the graph.
Discussion of Theory:
The method of continuous variations is very useful when determining the mole ratio of reactants when the formulas of the products are unknown. This method determines the ideal ratio of reactants by measuring the heat produced when the reactants are reacted in various ratios. The ratio that emits the most heat, or has the greatest change in temperature, is the best ratio. It is considered the best ratio because the reaction produces the maximum yield of heat when the difference in the starting temperature and ending temperature is the greatest. The optimum ratio is the soichiometric ratio in the equation for the reaction. This is calculated using the molarity given and the milliliters of the best ratio of each reactant.
For a ratio of compounds to be considered the best ratio, it must consume the largest amount of the reactants, as well as form the maximum amount of products. In this experiment, this was determined by the amount of heat released during the reaction. When heat is produced when two compounds are combined, a chemical reaction occurred. Therefore, the more heat that is produced, the stronger the reaction was. In other words, as more heat is produced, the maximum yield increases. In any reaction, the maximum yield of products is desired, and it is achieved by using the appropriate volumes of each reactant. Since the amounts of NaClO and Na2SO3 were unknown, different ratios of each were tested to determine which produced the most heat.
For a ratio of compounds to be considered the best ratio, it must consume the largest amount of the reactants, as well as form the maximum amount of products. In this experiment, this was determined by the amount of heat released during the reaction. When heat is produced when two compounds are combined, a chemical reaction occurred. Therefore, the more heat that is produced, the stronger the reaction was. In other words, as more heat is produced, the maximum yield increases. In any reaction, the maximum yield of products is desired, and it is achieved by using the appropriate volumes of each reactant. Since the amounts of NaClO and Na2SO3 were unknown, different ratios of each were tested to determine which produced the most heat.
Analysis Questions:
1. The volume of reactants was kept constant so that the variable being tested, in this case temperature, was isolated. When trying to determine the effects of varied ratios of reactants, the volume must remain constant so the results can be observed clearly and accurately.
2. The term "limiting reagent" is the compound or substance that is completely used up in the reaction, and therefore limits the amount of product can be produced from the other reactants.
3. The measurement that limits the precision of the data is volume. This is because the experimenter has control over how the volume of the reactants used in the experiment. Each trial, the volume may vary slightly, due to human error when pouring the reactants into the graduated cylinders and other measuring devices. If each trial of an experiment is varied slightly, the data's precision is limited. On the other hand, the experimenters do not have control of the temperature; for it is the value being measured in the experiment.
4. Along the upward sloping line of the graph, NaClO is the limiting reagent. This is because as more NaClO is added, the change in temperature increases, meaning the reaction is getting stronger. Along the downward sloping line of the graph, Na2SO3 is the limiting reagent. As more Na2S03 is added to the reaction, it becomes stronger, seen through the increasing change in temperature.
5. Physical properties like color intensity, mass of a precipitate and volume of gas formed in the reaction could all use the method of continuous variations.
6. It is more accurate to use the point of intersection of the two lines to find the mole ratio rather than the ratio associated with the greatest temperature change because this intersection represents the ideal ratio of reactants. The ideal ratio of reactants produces the best reaction, which is what should be used to determine the mole to mole ratio. This point may be in between the points of greatest temperature change, and not all points in between were tested. Therefore the intersection of the two lines is the more accurate point to use when finding the mole to mole ratio.
2. The term "limiting reagent" is the compound or substance that is completely used up in the reaction, and therefore limits the amount of product can be produced from the other reactants.
3. The measurement that limits the precision of the data is volume. This is because the experimenter has control over how the volume of the reactants used in the experiment. Each trial, the volume may vary slightly, due to human error when pouring the reactants into the graduated cylinders and other measuring devices. If each trial of an experiment is varied slightly, the data's precision is limited. On the other hand, the experimenters do not have control of the temperature; for it is the value being measured in the experiment.
4. Along the upward sloping line of the graph, NaClO is the limiting reagent. This is because as more NaClO is added, the change in temperature increases, meaning the reaction is getting stronger. Along the downward sloping line of the graph, Na2SO3 is the limiting reagent. As more Na2S03 is added to the reaction, it becomes stronger, seen through the increasing change in temperature.
5. Physical properties like color intensity, mass of a precipitate and volume of gas formed in the reaction could all use the method of continuous variations.
6. It is more accurate to use the point of intersection of the two lines to find the mole ratio rather than the ratio associated with the greatest temperature change because this intersection represents the ideal ratio of reactants. The ideal ratio of reactants produces the best reaction, which is what should be used to determine the mole to mole ratio. This point may be in between the points of greatest temperature change, and not all points in between were tested. Therefore the intersection of the two lines is the more accurate point to use when finding the mole to mole ratio.