Unknown Gas Test LabSetup and Debrief

Tahoma Jr. High8th Grade ScienceMaple Valley, WA

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 done anyway in case of fire)

* Check clothing, hairand jewelry

* Look before moving

and finally…PAY ATTENTION TO and FOLLOW

INSTRUCTIONS !!

Safety 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

Now 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.

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.

Have 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

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).

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.

Unknown Gas #1 Debrief

Showing what you did using a chemical reaction equation would look like this:

NaHCO3

(baking soda)

CH3COOH (vinegar)

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)

These would be the“products”

(what is made)

Since we start with a base – and then add an acid, you should know that there will be two products.

What are they?

NaHCO3

(baking soda)

CH3COOH (vinegar)

+ H2O + a salt

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!!

+ a gas

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?

NaHCO3

(baking soda)

CH3COOH (vinegar)

+ H2O + a salt

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!

+ a gas

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?

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)

You 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.

OK – that test is done. Cleaning up this time is a bit different – PAY ATTENTION

Zinc 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 equipment

Keep goggles for Test #3 demo

This reaction is much simpler and easyto see what’s happening.

Zn HCl+ H2 + ZnCl

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...

Zn HCl+ H2 + ZnCl

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!

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.

The first was to produce the hydrogen gas.

Zn HCl+ H2 + ZnCl

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 O2 H2O+

Remember hydrolysis where we split the water into hydrogen and oxygen gas? We just put it back together again using room

air oxygen!

heat

Things above/below the reaction arrow are other conditions needed for the reaction

+ energy

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?

Having 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 !

Now watch your teacher demonstrate

Unknown Gas #3

We 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…

What was interesting about this gas?

Did you notice how something not quite able to burn in room air suddenly burst into flame

inside the test tube?

Did you notice that the white powder turned to a dark purple/red?... and then boiled?

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?

More oxygen… that’s what!!

KClO3 MnO2O2

+ unimportant byproducts

The 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 CaCO3

Sugar (glucose) is C6H12O6 and is a “carbohydrate”

heat

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!!

C6H12O6 CO2+ H2O

Wood is a type of carbohydrate that plants make during photosynthesis

By burning it, we are doing a form of “respiration”: using oxygen to break down the sugar and release carbon dioxide and water.

heat+ O2 + energy

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