CHEM 167 L 177 L Chemical Reactions in the Atmosphere

Today we are doing chemical reactions in atmosphere for part one we are going to be collecting nitrogen and oxygen gas so we are going to need to label our flasks that we are collecting them in so first will label my N2 flask or nitrogen gas and then my oxygen flask or O2 now can move to collect my gas now have moved to begin collecting my nitrogen gas in order to do so we need three main components we need our gas cylinder with nitrogen gas our labeled nitrogen flex and our trough filled with tap water which is connected to our cylinder via this hose now let's take closer look at this gas cylinder here there are three valves here on the cylinder you will have your needle valve farthest to the left which may or may not be labeled with green tape this is the valve that you as the student will be using in order to collect your gas you will open it or close it in order to let gas out from the cylinder we have this knob or this valve right here which regulates our pressure this is going to be set by the lab staff please do not change anything it will be either taped red to signify you should not touch it or covered with plastic beaker so that you should not touch it as well we have the main valve here this as well may or may not be covered in red tape or will be covered with plastic cap the main valve will be opened by either lab staff or your TA here here's some additional useful information for TA should you ever find yourself with the gas cylinder not pushing out any gas even though you have the needle valve open there are three components you should check one make sure that your main gas valve is open if it is open and you are still not receiving any gas check to see if you have any gas remaining this dial here will tell you how much gas pressure is remaining inside the cylinder if it is starting to get too low you may not end up having enough pressure in the cylinder to emit any gas if this which is reading as it is now quite full then next you should check the pressure dial if the pressure gauge is sitting at zero then you will need to change the pressure valve in order to have gas come out of the cylinder the value that we set it at is between 10 and 20 psi so you will not need to have the gauge reading more than beyond this first or second hash mark here now am ready to collect my nitrogen gas in order to do this first will need to take my flask and fill it with tap water from the sink want to make sure the flask is overflowing with water let my bubbles escape and then I'll be taking my rubber stopper capping it very tightly in order to make sure that no air of any kind has gotten into my flask will then invert place into my trough and remove the stopper and now have my flask ready to go to collect gas so now you can see my trough is connected to my gas cylinder underneath through this tube if you could open up the gas please as you see am starting to have my gas bubble through an opening right down here in the bottom of the trough we are adjusting the speed to just very slow to moderate rate of bubbles forming next once the speed is at the correct amount move the mouth of the flask over top and can now begin collecting my gas and now wait until have collected almost the entire flask full of gas as you can see as the gas is filling inside of our flask the water that was previously inside the flask is being displaced and pushed into our trough now that we have gathered plenty of gas can go take my stopper reach back under and seal the flask it is very important to make sure that the neck of the flask stays under the water in the trough the entire time if at any point the flask is above the water you will end up contaminating your gas with air from the outside environment so now can take my sealed flask up and have my flask containing nitrogen gas since know that nitrogen gas is lighter than air gas prefer to keep my flask inverted like this with my water down at the neck near my rubber stopper this help this helps create an extra barrier against any air coming through since my nitrogen will naturally like to sit at the top and my water will sit at the bottom helping to prevent any nitrogen from escaping or air from entering next we will go and repeat this exact same step with oxygen so for this have my two flasks we are again going to need to label them this time however one flask will be labeled no one for our first flask and no two for our second flask the one and two are not correlated to the chemical formula whatsoever they are just to signify which flask is which here is my setup for my production and collection of nitric oxide gas have my copper turnings and nitric acid three molar have two grams of my copper turnings that will take and add right to my test tube need them as close to the bottom as possible so will take my glass stir rod and push them down to the bottom of the tube next I'll be adding 40 mL of three molar nitric acid now have my nitric acid that I'll be heating right at the top do not want to be heating directly on my copper nor do want to be heating up towards the top near my buret clamp otherwise may end up melting part of the burette clamp have my rubber stopper with glass bend connected to my water trough first edo collection flask and second eno collection flask this one will likely contain air this one should however be pure now can take and start my bunsen burner have very gentle flame so that can begin heating right at the top of my flask and will let this go in order to heat the reaction in order to start producing my gas so will take my first flask and place it over the opening and begin collecting now will show you how to properly prepare your syringe for when you are doing gas transfer so first have expelled all the air that is in my syringe by pushing the plunger all the way to the bottom now will take my tubing and push it under the water and pull in water into my syringe as you can see have an air bubble right here so was obviously not able to get all the air out of my tube or even out of my syringe in its entirety so in order to do that will invert my syringe here have my setup for combining gases to start I'm going to be using nitrogen gas as my gas of interest have already secured my hundred mil grad cylinder with water I'm going to uncap my nitrogen flask have purged my syringe so will just feed the tube up and then I'm going to take out 30 mL of nitrogen now will add that 30 mils of nitrogen into my graduated cylinder it is very important to keep all of my components underwater in order to prevent any air from entering the system there we go I've added my 30 mL of nitrogen and my cylinder is reading 30 mL so know that was accurate now will need to purge my syringe again so pull up some water invert and expel one more time pull up water invert and expel so now my syringe is good for the next gas that I'm going to use I'm going to be capping my nitrogen since no longer need it and then removing from my trough the gas that I'm going to be adding is my oxygen gas so I've placed that in my trough and am now removing the stopper can take my tube and feed into my flask and I'm going to be adding 5 mL of oxygen to my nitrogen now that my tube is in my graduated cylinder can expel my gas now took and added 10 mL in order to have very clear reaction and as can see when added my 10 mL of oxygen, now have total volume of 40 mL my graduated cylinder since the volumes were additive it means that there is no reaction between the gas there is also no color change so next I'm just going to be doing second trial to make sure that there is no reaction this time only took 5 mL adding my 5 mL has again left me at 45 mL in my graduated cylinder which means again the volumes were additive and there was no reaction between nitrogen or oxygen we will wait for approximately two minutes to confirm while am waiting can go ahead and purge my syringe to prepare it for my next combination about two minutes have passed and will double-check and still have no volume change which means that there has been no reaction between my oxygen and nitrogen here have my setup for collecting gases am going to be using oxygen this time as my primary gas of interest have purged my syringe already so I'm going to feed my tube up into my oxygen flask and take 30 milliliters of oxygen and then I'm going to add my oxygen to my graduated cylinder checking my graduated cylinder have 30 mL of gas in there so my addition went fine I'm now going to purge my syringe now that I'm done adding my oxygen can cap my oxygen flask and then remove it I'm going to be adding my nitric oxide to my oxygen am using my first flask of nitric oxide that gathered we know since this was our first flask it is not completely pure but for this case this slight impurity to it should not matter so I'm going to be adding two rounds of 5 mL of nitric acid or nitric oxide to my flask so I'm going to pull up about 10 mL but will add five at time this is in order to save having to reach into the flask an extra time have fed my hose up into my flask or my graduated cylinder now I'm going to add 5 mL for nitric oxide have 30 mL of oxygen in here as can see some brown gas has formed in my cylinder so since see presence of reaction I'm going to let it go for two minutes now that some time has passed I'm going to check my volume and see that my volume has actually decreased by milliliter so I'm now at 29 milliliters of gas in my graduated cylinder now let's repeat the addition with my remaining five milliliters of gas pay attention to the color in the tube in the cylinder and you see the moment added the gas we had very dark brown gas coalesce in our graduated cylinder as you also saw the volume was decreasing as the gas was forming now I'm going to check the volume one more time I've again lost one more mL so I'm now only at 28 mL of gas remaining in my graduated cylinder it appears that all of the brown gas has faded from my graduated cylinder due to the volume change and the color change we can know that there was some form of reaction between oxygen and nitric oxide gas in our graduated cylinder here is my gas setup for my final combination of gases I'm going to be using nitrogen again as my primary gas of interest as you can see just want to emphasize one last time have both of my flask and graduated cylinder clamped to help them stay secure but they are also elevated in my trough so the mouth actually has space between the bottom of the trough and the mouth of both the grad cylinder and flask in order to allow me to easily feed my tube up into the gas so have perched my syringe I'm going to be taking another 30 mL of nitrogen I'll be taking and adding my 30 mL of nitrogen to my graduated cylinder checking the volume I'm at 30 milliliters of nitrogen as would expect so will now purge my syringe be ready for my next guess now that my syringe is purged can cap my nitrogen and remove and now will be using my first flask of nitric oxide to test if there is any reaction between nitric oxide and nitrogen since this is the first flask that collected know that it is not totally pure but that is not important for this step here our impure version will work just as well as pure to test our reaction I'm going to be drawing 10 mL of nitric oxide I'm only going to be adding 5 milliliters at time for my two trials of 5 mL but I'm taking 10 that way do not need to go back into my nitric oxide flask so now that have my tube fed into my graduated cylinder I'm going to add 5 milliliters of nitric oxide there was no color change in the gas inside the cylinder looking at the volume am at 35 milliliters of gas which indicates that there should be no reaction going on will let this sit for moment just to make sure that there is no reaction going on before add my last five mills of nitric oxide now that it has sat momentarily can see that still have 35 mL of gas inside my grad cylinder signifying no reaction will add my last 5 milliliters again there was no color change and looking at the volumes am at 40 milliliters of gas in my grad cylinder so this confirms to me that there is no reaction between nitrogen and my nitric oxide gas will purge my syringe while wait to confirm that there is no reaction looking at the volumes it again has not changed so know for sure there is no reaction between my nitrogen gas and my nitric oxide here have my setup my quantitative analysis of oxygen and nitric oxide to start I'm going to take my 30 mL of oxygen now I've added my oxygen checking the graduated cylinder can confirm that have 30 mL of oxygen inside my grand cylinder so can now take and cap my oxygen flask and remove next I'm going to be using nitric oxide gas we are using our second collected flask because it should contain only nitric oxide and be pure rather than our first flask which could contain air and be impure so I'll take and uncap that now will purge my syringe have now purged my syringe so I'm going to feed it up into my flask and am going to be adding 10 mils of nitric oxide at time throughout this analysis so I'm going to draw up 50 mL initially so that can do five trials of 10 mL addition now that have my 50 mL can take and feed my hose up into my grid cylinder and now will begin my first 10 mL edition so as you can see we have very dark brown gas created also you can observe that there was volume change since our water level was increasing will let it sit for two minutes in order to allow the reaction to complete and then will read the water level in order to see if there was any form of volume change can see that there is no more brown gas in my cylinder after two minutes have passed so am going to look at the volume change and am now at 25 mL of gas in my cylinder so have lost five milliliters of gas in total i'm going to now add 10 milliliters again on my nitric oxide again deep brown gas has formed can already see that my water level is rising so will let this go for another two minutes and then will see if my volume changes the same or if it has not changed at all two minutes has passed and can see that there is no more ground gas in my bread and cylinder am now down to 20 milliliters in my graduated cylinder so I've again lost five milliliters of gas will now add another 10 milliliters of nitric oxide and will repeat the same step since before recording my observations dark brown gas has formed we are seeing volume change in the cylinder two minutes has passed am now down to nine milliliters of gas in my graduated cylinder which means likely added little more nitric oxide than intended since we could see pattern of losing five milliliters every 10 mL of nitric oxide added will again add another 10. the reaction has completed am now down to 10 mL my graduated cylinder will add my remaining 10 mL of nitric acid in my syringe and then will go and will retrieve 40 more milliliters of nitric oxide the reaction is completed in my graduated cylinder and am now down to 5 mL of gas left micro and cylinder so as you can see we have pattern of every 10 mL of nitric oxide added we lose 5 mL of gas that we initially had in our graduated cylinder now I'm going to see what happens with more additions of 10 mL nitric oxide I've added my 10 milliliters of nitric oxide the reaction has completed and am now at 7 milliliters of gas in my cylinder will add another 10. as we see now no more brown gas is forming in our cylinder and am now at 16 milliliters of gas in my cylinder you're starting to see additive volumes of gas so I'm adding another 10 milliliters of nitric oxide again no brown gas has formed am now at 26 milliliters of gas which means have total addition of gas now there is no more elimination will add my final 10 milliliters of nitric oxide and am now at 35 milliliters of gas which means that after added approximately 60 milliliters of my nitric oxide I'd eliminated any oxygen that was in my graduated cylinder when was creating nitrogen dioxide now after had added another 30 mL at the end had increased the volume of gas showing that there is no more oxygen remaining here have my nitric oxide flask it is my number one my impure version here is my suggestion after you have collected gas which can be your nitric oxide nitrogen and oxygen you can go ahead and store it upside down the reason we do this is because the water here creates very good seal with the rubber stopper this prevents any form of air getting in and prevents anything escaping as well to make this easy instead of setting your flask upside down on your counter like this you can take your plastic beakers and you can place inside sitting like that this gives you more stable flask to show as well it works with your 250 mL flask here have my oxygen again as you can see have extra water here and it can sit and stay stable on the counter top for actually likely several days