The objective of this experiment is to find the ratio that creates a large amount of heat energy that wholly utilizes substance ions that are thiosulfate ion (S2O32-) and hypochlorite ion (OCl–). After this, the equation will be balanced by using the coefficient that develops the mole ratio for the particular reaction.
A balanced chemical equation plays a significant role in providing mole ratios of reactants as well as products with the products as the coefficients which balances the equation. It becomes easier to balance the chemical equation once all formulas of reactants and products are well-known. A mole ratio determines how many moles of each chemical are to be used in a reaction to make it balanced and limits the amount of a limiting or excess reagent. Limiting reagents are the reactants that run out first and limit the amount of product that can form, and an excess reagent is a reactant that there is more than enough of to form a product and is often what is left after the reaction. Experimental measures can be utilized to make ratios when the formula of products is unknown. An example of an unbalanced and incomplete reaction is A OCL–(aq) + B S2O42-(aq) → products. A and B are the moles or coefficients that are needed for each compound to balance the equation. Measuring this heat to find the maximum temperature that will cause a reaction that completely consumes both ions, leaving behind no excess or a limiting reagent, will give you the mole ration for this reaction.
For this experiment, the materials needed were Logger Pro software on a computer and a LabPro data logger to collect information with a temperature probe. Other items that needed to be obtained are two 10-mL and two 25 mL graduated cylinders and Styrofoam cups. Also needed would be three 250 mL beakers to pour the solutions into and to give the cup extra stability. 0.5 molar solution of Na2S2O3 and 0.5 M solution of NaOCl in 0.2 molar solution of NaOH will be collected.
After the computer and all of the equipment were set up and logged in to LoggerPro, the file “07 was opened. After pair of goggles to wear were collected, the 50 mL of each of the reactant solutions, NaOCl and Na2S2O3 were placed in clearly labeled separate beakers. Exactly five ml solution of NaOCl was measured and put into the cup. The Styrofoam cup was placed inside a beaker for the purpose of stability. The temperature probe was placed in the solution of NaOCl then the “Collect” button was selected to begin collecting data from the initial temperature forward. The 0.5 mL of Na2S2O3 was added. After the introduction of Na2S2O3, the mixture was stirred continuously with the temperature probe. When the temperature readings from the data were no longer changing, the “Stop” button was clicked, and the maximum temperature change was recorded and determined. By using the Statistics button in LoggerPro, the minimum and maximum temperatures were found on the graph. After rinsing the cup and disposing of the solution into the waste bottle in the fume hood, the experiment was repeated, testing different ratios of the two solutions, and this would be repeated several times. The second trial used 6 mL of NaOCl and 4 mL of Na2S2O3, as the total volume was always 10 mL to have constant results. The remaining trials used ratios of 3.0 mL Na2S2O3 and 7.0 mL of NaOCl, 6.0 mL of Na2S2O3 with 8 mL of NaOCl, and 7 mL of Na2S2O3 solution and 3 mL of NaOCl. Other used ratios include 2 mL Na2S2O3 with 8 mL of NaOCl, 2.5 mL Na2S2O3 solution and 7.5 mL of NaOCl solution, 1 mL of Na2S2O3 solution, and 9 mL of NaOCl.
The highlighted data was the data surrounding the highest temperature change recorded. The max change would occur between 7.5 mL of NaOCl and 8 mL of NaOCl. The ratio of 8:2 is the same as 4:1 for the maximum and thus the perfect ratio as there were not any limiting or excess reagents.
Results and Discussion:
As the trials were being performed to find the perfect ratio the temperatures had a steady increase. Looking at the highest temperature on the graph, it was determined that the maximum reading was at a ratio of 8.0 mL of NaOCl and 2.0 Na2S2O3 with a temperature of 17.99°C. This ratio of 8:2 can be simplified to 4:1 and was shown on the graph as an intersection point. The ratio of 9:1 proved to give a temperature much lower temperature as was expected, with 10 mL of NaOCl having a temperature change of 0°C. When OCl was less than 8 mL, it was the limiting reagent, but when it was greater than 8 mL, S2O3 was the limiting reagent.
If the concentrations of these solutions were different, then they would have reacted differently as a base reacts with an acid.
The true balanced equation is 4OCl + S2O3 = 4Cl + SO3 +SO2 +O2. This follows our ratio of 4:1.