EXPERIMENT #9: Gas Laws and Gas-Forming Reactions Introduction: In this experiment you will use experimentation to analysis Boyle’s Law. In addition, you will do an experiment involving the collection of a gas to determine the percent yield of a gas forming reaction. Of the different physical states, the properties of gases vary the most with temperature and pressure. If the temperature of a gas changes the pressure or volume will change as well. When collecting gases in experimentation, a sealed container is necessary so that the gas does not escape. There are several different gas laws that help describe the behavior of gases. One gas law is known as Boyle’s Law, which was originally published by Robert Boyle in 1662. Robert Boyle found that the pressure of a gas and the volume of a gas are inversely proportional as long as amount and temperature are held constant. In other words, as the pressure of a gas increases the volume will decrease. The following equation is the mathematical expression for Boyle’s Law: 𝑃1 𝑉1 = 𝑃2 𝑉2 In this experiment the pressure of the syringe initially is equal to the room pressure, however once the weights are put on the plunger the pressure in the syringe decreases. In order to calculate the pressure in the syringe once the weights have been put on the plunger the following equation must be used: 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒𝐹𝑖𝑛𝑎𝑙 = 𝑅𝑜𝑜𝑚 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 − 𝑀𝑎𝑠𝑠 𝑜𝑛 𝑃𝑙𝑢𝑛𝑔𝑒𝑟 × 0.1561 𝑎𝑡𝑚/𝑘𝑔 Another gas law used in this experiment, is arguably the most important. The ideal gas law allows us to determine either the pressure, amount, volume, or temperature of a gas if we know all the other values. In this experiment we will know the pressure, temperature, and volume of the gas, we will then use the ideal gas law to determine how many moles of gas were formed from a chemical reaction. The ideal gas law is often used when doing stoichiometry for a chemical reaction that involves gases. The following is the equation for the ideal gas law: 𝑃𝑉 = 𝑛𝑅𝑇 In this equation P is for pressure and must be in atm, V is for volume which must be in 𝑎𝑡𝑚∙𝐿 liters, n is moles of gas, R is the ideal gas constant which is 0.08206 𝑚𝑜𝑙∙𝐾, and T is for temperature which must be in kelvins. If in a chemical reaction one of the products or reactant is a gas and is described using the pressure, temperature, and volume the ideal gas law can be used to determine the moles of gas present and then using moles you can then solve a stoichiometry problem. Otherwise, stoichiometry might be needed to find moles of a specific gas, so that the volume, pressure, or temperature of a gas could be determined. In this lab the reaction of sodium bicarbonate with hydrochloric acid is investigated, the equation for this reaction is seen below: 𝑁𝑎𝐻𝐶𝑂3 (𝑠) + 𝐻𝐶𝑙(𝑎𝑞) → 𝑁𝑎𝐶𝑙(𝑎𝑞) + 𝐻2 𝑂(𝑙) + 𝐶𝑂2 (𝑔) Experimental Procedure: Instructor Demonstration: Invisible Can Crush 1. First take a soda can and add a small amount of water to it. 2. Place the soda can on a hot plate and turn it up so that the water will begin to boil. 3. Then make an ice bath in a small bowl, and once the water in the can is boiling using beaker tongs quickly flip the can over into the ice water. Experimental Procedure: Boyle’s Law 1. Obtain a 60 mL syringe and a syringe cap, ensure that plunger is lubricated. Set the syringe to 25 mL and attach the syringe cap. Make sure the cap is screwed tight and the syringe is sealed tight by pushing the plunger in just a little and checking to make sure it moves back to 25 mL. 2. Using a two or three prong clamp secure the syringe on a ring stand relatively high up with the plunger pointed down. Then attach your test clamp onto the plunger. Place a 1 kg weight on the test tube clamp. See picture below. 3. Gently tap the syringe so that the volume stabilizes. Record the volume on the syringe. 4. Add a second 1 kg weight to the previous weight and record the volume a second time. 5. Calculate what the volume should have been using Boyle’s Law with the initial pressure, initial volume, and final pressure, for when there was only a 1 kg weight on the plunger and when there was a 2 kg weight on the plunger. 6. Using the measured volume and the actual volume from Boyle’s Law calculate the percent error of the measurement. Apparatus for Boyle’s Law Experiment Experimental Procedure: Reaction of Baking Soda and Acid Safety: 6M HCl, is hazardous to your skin and can cause burns and irritation, avoid contact with your skin, by wearing gloves. If HCl does come in contact with your skin wash the affected area with DI water for 15 mins. 1. Obtain an Erlenmeyer flask with spigot, a thick-walled test tube, two stoppers with rubber hosing, and a gelatin capsule from the cart. (There are two different stoppers with rubber hosing you need one of each). 2. Fill the Erlenmeyer flask with about 100 mL of deionized water, attach the rubber hose with the smaller stopper and glass tube attached to it to the spigot on the Erlenmeyer flask. 3. Put the stopper with the longer glass or metal tube and the bigger stopper into the top of the Erlenmeyer flask. Make sure both the hose and the stopper are well sealed. 4. Put the end of the hose coming from the top of the Erlenmeyer flask. Then attach a pipette pump to the end of the glass rod that is attached to the hose on the spigot of the Erlenmeyer flask and apply suction until the water in the flask raises to about 1 cm below the spigot. Clamp the hose with the pump on it with a hose clamp. 5. Empty the beaker of water and measure the mass, there is no need to fully dry the beaker. 6. Measure the mass of the gelatin capsule empty, then begin to add sodium bicarbonate into the capsule until there is about 0.3-0.4 grams of sodium bicarbonate in the capsule, record the mass of the capsule and sodium bicarbonate. 7. Clamp the test tube on a ring stand with a two or three prong clamp. Then measure out about 10 mL of 6 M HCl with a graduated cylinder, and pour it into the test tube. 8. Place the gelatin capsule with sodium bicarbonate in it, into the test tube make sure it is touching the HCl solution. Place the stopper connected to the spigot into the test tube tightly, and remove the hose clamp. Water will begin to flow into the beaker once the reaction starts. 9. Measure the mass of the beaker with the water in it and record the temperature of the water in the beaker. Apparatus set up for Reaction of baking soda and Acid. Name: ______________________________ Instructor Initials: _________ Experiment 9: Gas Laws and Gas-Forming Reactions Instructor Demonstration Observations: What happened in the demonstration to the soda can, and why did it happen? What gas law is being demonstrated in what you saw? Data and Calculations: Boyle’s Law: 1kg Weight 2 kg Weight Initial Volume of Syringe: ____25.0 mL__ _____25.0 mL__ Final Volume of Syringe: _____________ ______________ Initial Pressure in Syringe (provided by instructor): _____________ ______________ Final Pressure (actual pressure): (Calculated using mass equation) _____________ ______________ Final Pressure (measured pressure): (Calculated using Boyle’s Law) _____________ ______________ Percent Error in Final Volume: _____________ ______________ Calculations: Reaction of Baking Soda and Acid: Mass of Gelatin Capsule empty: _______________ Mass of Gelatin Capsule with sodium bicarbonate: _______________ Mass of empty Beaker: _______________ Mass of Baking Soda Used: _______________ Mass of Beaker with Water: _______________ Temperature of Water in Beaker: _______________ Density of Water: _______________ Mass of Water in Beaker: _______________ Volume of Gas Formed: _______________ Pressure of CO2 (Provided by Instructor): _______________ Room Temperature: _______________ Mass of CO2 Gas formed (Calculated using Ideal Gas Law): _______________ Theoretical Yield of CO2 Gas: _______________ Percent Yield: _______________ Calculations: Experiment 9: Post-Lab Assignment 1. What are some possible reasons for the percent error you measured in the Boyle’s Law part of the experiment? 2. What could be some reasons your percent yield for the decomposition reaction was not exactly 100%? 3. The decomposition of sodium azide is commonly used in car airbags, when the sodium azide decomposes it forms nitrogen gas which inflates the air bag. If you want to make 60.5 L of nitrogen at 25.0 °C, and 1.00 atm of pressure from this decomposition reaction, how many grams of sodium azide (NaN3) would need to decompose? Use the following unbalanced equation. 𝑁𝑎𝑁3 (𝑠) → 𝑁𝑎(𝑠) + 𝑁2 (𝑔) 4. If a balloon initially has a pressure of 1.456 atm and a volume of 1.32 L, what would be the pressure after the volume decreases to 0.543 L? 5. If a syringe with a plunger has a volume of 56.2 mL at 25.0 °C, what would the volume be if the temperature was changed to -15.6 °C? Name: ______________________________ Experiment 9: Pre-Lab Assignment 1. What two gas laws are being used in the experiment? 2. What is the equation for percent error used in the Boyle’s law part of the experiment? (We used this equation in Experiment 1) 3. About how many grams of sodium bicarbonate will be used in the decomposition of baking soda part of the experiment? 4. If the initial pressure of a container is 0.658 atm and the initial volume is 35.6 mL, what will be the pressure if the volume is decreased to 15.8 mL? 5. Using the equation in the introduction, determine what the pressure within the syringe would be if the initial pressure in the room is 1.013 atm and a 1.5 kg weight has been added to the plunger of the syringe.
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