Chem/Bio question (1 Viewer)

[genril]

Posting it here rather than the bio or chem forum because it is kind of general.

"Carbon Dioxide (CO2) can be made by adding Hydrochloric Acid (HC1) to Marble Chips (CaCO3). This is the method you will use to generate the gas. How you collect the gas, dissolve it and test for changes in pH is to be determined by the group or individual"

Now, How do I collect the gas? I have never done anything like this before, and if it was upto me I would be getting a straw and blowing the carbon dioxide into the beakers (I will be asking if I can do this, it works ).

Thanks.

Oh and by the way, this is for the bio experiment where we have to demonstrate the effect of dissolved carbon dioxide on the pH of water.

 

[Kujah]

Well, the first thing is that the HCl and CaCO3 would be added into a test tube. A cork with a hole would be placed on top of the test tube to ensure that any gaseous reactants could only escape through the hole in the cork.

So to ensure that we actually collect the gas, we'd add one of those tubes (the ones that look similar to the tubes we attach the Bunsen burner to the gas) into the hole, and on the other side of the tube, (this is guessing now), you'd probabaly just add another test tube with a cork in it.

If you're confused by what I've said, have a look at this image:

Someone help clarify me if I'm wrong :/

 

[genril]

Alright, I kind of understand what you're saying.

So I would place the marble chips and hcl in a test tube with a cork inserted, there will be a hole in the cork through which a tube will be placed.

could you please link the picture instead of putting it in image tags?

and, what do i do with the gas once it is in the other corked test tube... I need to get it into water some how, if I take off the cork to add water it will escape, right?

 

[Kujah]

http://www.gutenberg.org/files/16593/16593-h/images/image_024.jpg

That's the problem. Maybe you initally add the water into the second test tube, and then you can observe the results when the CO2 reacts with it without taking the cork out.

 

[sle3pe3bumz]

Okay mines very similar to Kujahs but yeah. I can't see the pic. =/

Measure pH of water first. Then place the marble chips into the test tube with HCl. Cork and tube the test tube. Now place the tube INTO the water (that should be in a beaker) which you measured and therefore the water should take up all/most of the CO2. Then you should measure the pH of the water after.

Well thats just how I'd do it. So yeah ..

 

[genril]

But how will the gas get out of the test tube after you place it in the water?

I don't get it.

 

[morganforrest]

It's an equilibrium reaction....only some of the carbon dioxide produced will dissolve into the water to form carbonic acid and this is a function of the temperature of the water.

Get a (I cant quite remember what they are called) side arm conical flasks. Marble and HCl in the bottom with the cork in and a rubber hose attached to the side arm. Pipe this into a beaker or conical flask with water (Deionised water so u know exact pH of 7 which you would test with a pH probe)

After all the CO2 has bubbled through you can test the pH again.

However note that the equilibrium is CO2 + H2O <=> H2CO3

To push the equilibrium to the right, forming more products and hence lowering the pH of the water you should increase pressure and decrease temperature (hence why coke has more fizz when its just opened after having been chilled)

So understanding this factor you could add some indicator (universal or bromocresol green imo) to the water in ur secondary side arm conical flask, ensure the cork is in quite tightly (do this in the fume hood in case it shatters the glass/shoots cork out randomly) and observe the change in indicator colour as the solution becomes more acidic.

Sorry I don't have a photo of it but I hope that explains 2 ways of approaching this problem.

 

[genril]

Okay I get that, thanks alot.

I don't think they want us to do it in so much depth though as it is only bio and not chem, they want us to test the effect of co2 on h2o pH levels.

So, would this just mean setting up 3 beakers, and a tube going into each, then set up the reaction and allow the gas to transfer into the water for a set time period, which is different for each beaker, along with having a seperate control?

Like so:

 

[morganforrest]

If they just want a rough idea of pH, stick some universal indicator in one that's under pressure and watch how it changes.

But your idea will work