The Decomposition of Potassium Chlorate, Lab Reports of Chemistry

Download The Decomposition of Potassium Chlorate and more Lab Reports Chemistry in PDF only on Docsity! E4C-1 Experiment 4C FV 1-21-16 THE DECOMPOSITION OF POTASSIUM CHLORATE MATERIALS: test tubes: (25x150 (Instructor Demo, Part A), 18x150 (Part B)); 100 mL beaker, glass wool, potassium chlorate, manganese(IV) oxide. PURPOSE: The purpose of this experiment is to study the decomposition of potassium chlorate and quantitatively determining the correct stoichiometry. LEARNING OBJECTIVES: By the end of this experiment, the student should be able to demonstrate the following proficiencies: 1. Find the MSDS and/or Safety Card for a chemical species, and locate important information related to physical properties, reactivity, and appropriate handling protocols. 2. After carrying out the decomposition reaction for potassium chlorate, quantitatively verify its stoichiometry. DISCUSSION: Stoichiometry. A major emphasis of chemistry is the understanding chemical reactions. This requires knowing the correct formulas for all reactants and products involved in the reaction, as well as the relative molar amounts of each. Such information is provided by the balanced chemical reaction, but where does that come from? The answer is that reactions are determined by experiment. Careful mass measurements and physical and/or chemical tests allow one to deduce the proper reaction. Only when that is understood can one start to consider useful applications of the reaction. Consider the title reaction, the thermal decomposition of potassium chlorate. When KClO3 is heated strongly, it breaks down releasing oxygen gas and leaving behind a thermally stable (i.e., heat-insensitive) solid residue of an ionic potassium compound. solid potassium chlorate  oxygen gas + solid residue There are at least three plausible reactions one can write for the process, but only one occurs to any significant extent. Which one is actually observed can only be determined by experiment, such as those conducted here. By measuring the amount of oxygen lost when a sample of potassium chlorate is heated, we will be able to determine the stoichiometric coefficients of KClO3 and O2 in the reaction, and thus determine the correct reaction. Relevant Naval Application. On submarines, oxygen for breathing is normally produced through electrolysis of water. Details relating to this process will be studied later in the course. In an emergency, a chemical process is used to produce oxygen gas for breathing, specifically the decomposition of sodium chlorate at high temperature (i.e., above 300oC), producing oxygen gas and a solid sodium salt. Unfortunately, there are several complications associated with this reaction which must be remedied if the production of oxygen gas for breathing is to be performed safely and efficiently in this practical application. First, though the decomposition reaction occurs at temperatures above 300oC, it is extremely slow and therefore impractical for oxygen production in bulk. This is remedied by adding a catalyst, in this case manganese(IV) oxide, which significantly increases the rate of the reaction, without itself being consumed. Second, the intense flame used to raise the temperature of the sodium chlorate above 300oC is produced by a combustion reaction, which consumes large quantities of oxygen gas, whereas the purpose of the overall process is to produce oxygen gas. While this issue cannot be completely remedied, small amounts of iron metal are mixed in, reacting with some of the oxygen to produce iron oxide and releasing large quantities of E4C-2 energy which helps maintain the mixture above the 300oC decomposition temperature. After the “candle” is ignited, the oxygen-consuming flame used to initiate the decomposition reaction is replaced by this iron combustion process, making it more self-sustaining. Third, while the desired decomposition reaction predominates, there is another decomposition reaction which produces toxic chlorine gas, oxygen gas and sodium oxide. This is remedied by including small amounts of barium peroxide in the mixture, which reacts with the toxic chlorine gas to produce barium chloride and oxygen gas. In summary, the “chlorate” or “oxygen” candle used for emergency production of oxygen gas for breathing on submarines consists of a mixture of sodium chlorate, iron, a small amount of barium peroxide, and a fibrous binding material. In practice, each candle burns near 400oC for 45-60 minutes, and produces approximately 115 SCF (standard cubic feet) of oxygen gas at 0.5 psig (pounds per square inch, gauge pressure), which is enough oxygen for about 100 people. The stored candles represent a significant fire hazard since they are self-sustaining in oxygen. Use of potassium chlorate. In this experiment, potassium chlorate will be used instead of the sodium chlorate employed commercially. As you should suspect, analogous reactions occur, with all of the same complications. The only remedy that will be applied here will be the inclusion of the manganese (IV) oxide catalyst. Since all of the procedures will be carried out in the fume hood, any toxic chlorine gas produced will be safely carried away in the ventilation system. Why is NaClO3 used commercially, rather than KClO3? The principal reason is cost; sodium salts are typically much less expensive than their potassium counterparts. Material Safety Data Sheets and International Chemical Safety Cards. Any institution where chemicals are used is required to have copies of the material safety data sheets (MSDS) or safety data sheets (SDS) available for use. These sheets provide key information relating to health hazards, appropriate storage, handling and disposal arrangements, fire and explosive hazards, required control measures, physical/chemical properties, and reactivity data. In this experiment, the MSDS for potassium chlorate will be used to help guide the experimental study of its decomposition reactions. In general, prior to any chemical procedure, the relevant MSDS should be consulted to assure safe and proper procedures are followed. Another system which provides similar information is the International Chemical Safety Card system. Both MSDS and Safety Cards are available on-line through links found on the Plebe Chemistry homepage. Figure 1. Examples of oxygen candles. Various candle sizes are manufactured for different applications. While oxygen candles are most commonly used for emergency purposes on submarines, they are also used in spacecraft, refuge shelters in underground mines, and emergency shelters. One manufacturer claims that with a shelf life of 10 years, one oxygen candle produces enough O2 to keep 15 people alive for 5.7 hours, assuming they are at rest (calculation based on 0.5 L per person per minute). E4C-5 Name _____________________________________ Section _____________ IN-LAB QUESTIONS  Experiment 4C Complete these questions during lab. 1. What was the fuel (combustible material) that was added to the hot KClO3? What happened when it was dropped into the test tube? 2. Was the process of combustion of the fuel endothermic (absorbs energy) or exothermic (releases energy)? What evidence do you have for that? 3. What did you observe as you heated the mixture of KClO3 and MnO2? How could you identify when the decomposition process started and when it was complete? 4. Consider the process of melting the solid KClO3: KClO3 (s)  KClO3 (ℓ) Is this process endothermic or exothermic? Explain your answer. 5. Which of the two energy diagrams best describes the process of the melting of KClO3(s)? Circle it. KClO3 (s) KClO3 (ℓ) _________________________ ________________________ Energy Energy KClO3 (ℓ) KClO3 (s) _________________________ ________________________ E4C-6 6. If the experiment is carried out properly, any mass lost during heating must be due to oxygen gas that escaped when the KClO3 decomposed. Based on your data, how many grams of oxygen gas escaped during the decomposition? How many moles of O2 (g) is this? Show your work. 7. Based on your data (and assuming complete decomposition of the sample), what mass of KClO3 was decomposed in your experiment? How many moles of KClO3 (s) is this? Show your work. 8. Based on your data and the answers above, what is numerical value of the mole ratio between O2 and KClO3? Show your work.  decomposedKClOmoles producedOmoles 3 2 Report your value for inclusion with the class data. Hood Class Data for moles O2/moles KClO3 1 2 3 4 5 6 7 8 9 10 Average Based on the class data, and removing any outlying results, what is the average value? E4C-7 9. Which of the three reactions in the Pre-Lab best fits your experimental data (circle it)? Explain your answer. ? 3 2  decomposedKClOmoles producedOmoles a. ___ KClO3 (s)  ___ KClO2 (s) + _____ O2 (g) __________ b. ___ KClO3 (s)  ___ KClO (s) + _____ O2 (g) __________ c. ___ KClO3 (s)  ___ KCl (s) + _____ O2 (g) __________ POST-LAB QUESTIONS 1. Ignoring any side reactions and assuming the reaction occurs completely and by the stoichiometry determined in the experiment, how large (in kg) an oxygen candle (KClO3) would be needed to supply 8 people with enough oxygen for 24 hours on a small submarine? Although this depends on the size of the person and their respiration rate (activity), according to NASA1, an average person needs about 0.84 kg of O2 per day. 2. Magnesium chlorate solid thermally decomposes to form magnesium chloride solid and oxygen gas. a. Write the balanced chemical reaction for this decomposition. Include the states. b. If 2.50 g of magnesium chlorate is decomposed, assuming complete reaction, how many grams of oxygen gas are formed? Show your work. Report answer with proper significant figures. 1Wieland, P.O., Designing for Human Presence in Space: An Introduction to Environment Control and Life Support Systems, NASA Reference Publication 1324, 1994, pp. 6, 183-262.