Presentation on theme: "Unknown Gas Test Lab Setup and Debrief Tahoma Jr. High"— Presentation transcript:
1Unknown Gas Test Lab Setup and Debrief Tahoma Jr. High 8th Grade ScienceMaple Valley, WA
2* Keep your work area clean * Get bags out of walkways Before we setup this lab, we need a reminder of the FIRST thing that ALWAYS should be on your mind during science labs – SAFETY !! - especially with flame, chemicals, etc.* Keep your work area clean* Get bags out of walkways(this should always be doneanyway in case of fire)* Check clothing, hairand jewelry* Look before movingand finally…PAY ATTENTION TO and FOLLOW INSTRUCTIONS !!
3Safety also includes using equipment properly. Keep the following in mind…* Open flames require constant awareness* Glassware needs extra care (it gets hot)* Chemicals need to remain pure until mixed* Do NOT make sudden movements in a lab* Know where safety equipment is and how to use it(locate fire extinguisher/blanket, eyewash, 1st Aid Kit)* Follow instructions CAREFULLY
4Now let’s get to testing Unknown Gas #1 First, get your lab area setup (clear, organized and with equipment ready to go).We’re going to light a candle to be a flame source for your tests (goggles on). Do NOT play with the fire/candle – burn only a small bit of wood each test.Playing with fire is VERY unsafe and will lead to IMMEDIATE suspension or worse.Also, be sure not to reach across your table while there’s a flame!! Keep the candle in the center of the table so everyone knows where it is.
5Be Careful – the test tube top will get HOT !! CONTROL: test regular air in your test tube by lighting a wooden splint and inserting it into the open end while the tube is at a slight angle.Do this a few times and observe carefully what happens to the flame and how quickly it happens.Be Careful – the test tube top will get HOT !!Record your time/resultsin the space providedon your worksheet.
6Have someone go to the chemical supply table with the test tube and put in ~1cm (width of a pinky) depth of baking soda (sodium bicarbonate or NaHCO3) into the tube – along with a couple large squirts of vinegar (acetic acid, CH3COOH).Gently cover the top - return to table.+Carefully:feel the bottomof the test tube with vinegar and baking soda reacting
7Feel the bottom of the test tube and make any observations Feel the bottom of the test tube and make any observations. Then insert a flaming splint into the angled test tube and notice if anything different happens compared to an empty tube.Look at the chemical formulas and see if they give any clues as to why things happened this way (think of what you already know about putting out fires).
8DON’T EVER JAM PAPER DOWN INSIDE OK – time to clean up and get ready for the Debrief now that the test is done. Carefully clean out your test tube with the test tube brush (you can flush chemicals down the sink) and then FIRMLY holding the test tube, gently shake the excess water out in the sink.DON’T EVER JAM PAPER DOWN INSIDEA TEST TUBE OR YOU WON’T GET IT OUT !!Leaving a little water inside is OK anyway.Put test tube in beaker so it won’t roll off table and break.
9These are the “reactants” Unknown Gas #1 DebriefShowing what you did using a chemical reaction equation would look like this:?NaHCO3(baking soda)+CH3COOH(vinegar)These would be the“products”(what is made)These are the “reactants”(or “reagents”)The arrow means “goes to”or “turns into” and shows the direction of the reaction(usually going left to right)
10Since we start with a base – and then add an acid, you should know that there will be two products. What are they?H2Oa salta gasNaHCO3(baking soda)+CH3COOH(vinegar)++This is the end result (the initial reaction is a bit more complicated and not important). The important part of it, though, is that a gas is produced and released. Do you see anything in the reactant formulas that may give you a clue as to what gas might be produced that could put out fires?Look closely and think!!
11You might think hydrogen gas could be produced from the vinegar – OK You might think hydrogen gas could be produced from the vinegar – OK. But also look at the baking soda – is there something familiar there that may put out fires?H2Oa salta gasNaHCO3(baking soda)+CH3COOH(vinegar)++Good! CO2 gas is produced from the CO3 (carbonate) and this is what’s in many fire extinguishers. Carbon dioxide is a heavy gas and smothers a fire by not allowing oxygen to reach the fuel and heat source to keep the reaction going. What’s funny, is there’s lots of oxygen in CO2, but it’s double-bonded together and can’t get loose to react!
12Room air is what you tested first for a “Control” to compare to. Since the CO2 was heavy, it pushed out all the room air which is made of:78% N2 (nitrogen - which won’t react with anything) and 21% O2 (oxygen)Room air is what you tested first fora “Control” to compare to.Without ANY oxygen, theFlame went out very quickly!!Did you notice anything about the bottom of the test tube during the reaction?Was it cool to the touch?
13So, we’ve learned how to produce and test carbon dioxide (CO2) gas So, we’ve learned how to produce and test carbon dioxide (CO2) gas. Let’s try another one.Unknown Gas #2Put ~1cm of HCl acid in your test tube and grab a few pieces of zinc metal (Zn). Once back at your table with a flame ready, TILT your test tube a bit and SLIDE the zinc down inside to start reacting.BE CAREFUL! – this acid is fairly concentrated!Avoid getting any on you or your clothes.Cover the top with your thumb (or the fleshy part of your hand below your thumb) to trap the gas and feel the bottom of the tube. (see next slide before doing)
14You will feel pressure building up – try to keep it trapped as much as possible and then get someone to put a flaming splint next to the top at the same time you take your hand away.DON’T FREAK OUT – it won’t hurt you!Observe a sample of pure, clean zinc at the front table, do experiment and then record results.Look at the chemical formulas and try to write a reaction equation that may show what gas is being produced that could have this result with a flame test.
15Zinc CANNOT go down the drain OK – that test is done. Cleaning up this time is a bit different – PAY ATTENTIONZinc CANNOT go down the drain(other chemicals are safe when diluted)* add water to test tube to dilute the acid* put fingers over the end and turn upside down to let diluted acid out but keep zinc in - do this twice* put zinc on the paper towelat the front of the room to dry* dry out test tube by gently shaking* wet down all burned wood, put in awet paper towel and throw out – return equipmentKeep goggles for Test #3 demo
16Zn HCl H2 ZnCl This reaction is much simpler and easy to see what’s happening.Zn+HClH2ZnCl+We know we got hydrogen gas because of the flame test reaction… it exploded! COOL!!(actually it was HOT!)That was one obvious observation – there should have been three others...
17First, the bottom of the test tube this time got VERY hot First, the bottom of the test tube this time got VERY hot. Lots of bonds were breaking releasing their energy – that’s what acids (and bases) do!Zn+HClH2ZnCl+Second, the zinc turned from a shiny silver color to a grey color (this was the chlorine combining with it after releasing the hydrogen.Third, did anyone notice what happened at the top of the test tube after “popping” the hydrogen??Exactly! There was some “fog”. What could this be?We actually were doing two reactions.
18The first was to produce the hydrogen gas. ZnHClH2ZnCl++The second reaction was “popping” the hydrogen by burning it. You need 3 things for fire: fuel (H2), heat source (the flame) and…?oxygen !!H2+O2H2O+energyheatThings above/below the reaction arrow are other conditions needed for the reactionRemember hydrolysis where we split the water into hydrogen and oxygen gas? We just put it back together again using room air oxygen!
19This is one of the most famous pictures in history This is one of the most famous pictures in history. It’s of a large airship called a dirigible or zeppelin named the Hindenberg.Germany led the worldin airship technology until in 1937 the Hindenberg was landing in New Jersey and something triggered an explosion (static electricity?, lightning?, sabotage?, no one knows for sure).36 people died… guess what lightest gas was in it?
20Having learned from this mistake (which ended the era of large hydrogen filled airships with metal frames) today’s airships are soft balloons called “blimps”.Blimps are filled with an inert light gas that won’t react. These are all the “Noble” gases on the right side of the Periodic Table in Group 8 - and the lightest is…?helium !
21Now watch your teacher demonstrate Unknown Gas #3We would have liked to allow you to do this one too, but previous experience has shown it’s a bit too dangerous for 8th Grade students… sorry…
22What was interesting about this gas? Did you notice that the white powder turned to a dark purple/red?... and then boiled?Did you notice how something not quite able to burn in room air suddenly burst into flame inside the test tube?What gas would cause something barely glowing to burst into flame? We have fuel (wood), heat (the glowing part of the wood not quite burning)… what else is needed?
23KClO3 O2 More oxygen… that’s what!! + heatO2+unimportant byproductsMnO2The manganese dioxide (MnO2) only helps the reaction go (it’s called a “catalyst”). The heat is breaking down the potassium chlorate (KClO3) allowing the oxygen to bubble out.When you see a chemical end in “-ate”it means LOTS of oxygens!Calcium carbonate (chalk/limestone) is CaCO3Sugar (glucose) is C6H12O6 and is a “carbohydrate”
24Wood is a type of carbohydrate that plants make during photosynthesis Once we made the oxygen, we reacted it with the glowing wood to make it re-ignite, or a flame burn the wood faster/brighter!!heatC6H12O6O2CO2+H2O++energyWood is a type of carbohydrate that plants make during photosynthesisBy burning it, we are doing a form of “respiration”: using oxygen to break down the sugar and release carbon dioxide and water.
25(make a flashcard for each flame test for each gas) SUMMARYTEST MATERIAL !!(make a flashcard for each flame test for each gas)(baking soda + vinegar) makes…CO2 - flaming splint goes out quickly(Zn + HCl acid) makes…H2 - flaming splint “pops” / explodes(potassium chlorate + heat) makes…O2 - flaming splint burns brighter – glowing splint re-ignites into flame