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Laboratory Investigation III: Carbon Dioxide Production

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Carbon Dioxide Introduction 0:06
    • Purpose
    • Materials
    • Time
  • Part I 2:41
    • Put Water in Large Beaker
    • Exhale Into the Water
    • Add a Drop of Phenolphthalein
    • Add NaOH
    • Record the Amount of Drops
  • Part II 6:24
    • Add HCL
    • Exercise for Five Minutes
    • Return and Re-Do the Exhaling
  • Analysis 9:11
  • Aerobic Respiration Connection 13:18
    • As Aerobic Respiration Occurs In Cells, Carbon Dioxide Is Produced
    • Increase Output of Carbon Dioxide
    • Number of Exhalations Increase

Transcription: Laboratory Investigation III: Carbon Dioxide Production

Hi, welcome back to, this is laboratory investigation 3, carbon dioxide production.0000

With the CO₂ lab, the purpose is to measure the difference in CO₂ production in humans, before and after exercise.0008

When I do this with students in a classroom, it is very interesting the reaction of this.0019

Because, they go into it just thinking that this is a fun lab where I exhale through the straw into the solution.0024

It is fun, while I’m doing it 4 min we are going to have this color change, it is going to be great.0030

They find out they have to go exercise during a part of it.0036

I do not think this is going to be PE, physical education.0040

Biology, study of life, it is important to engage in physical exercise.0046

That is a crucial part of this lab, in terms of measuring how doe CO₂ is exiting the body, before and after exercise.0050

The materials are two beakers, one large and one small.0056

Here is an array of beakers, you can use this one and that one, you can use this one and that one.0059

It really does not matter the exact size, as long as they are all above 50 ml.0065

Just a medium sized beaker will do.0072

You are going to put 50 ml of distilled water into the larger one.0075

You are going to put 20 ml of one mole dilute concentration or even more dilute of sodium hydroxide, nah.0080

You do not actually need a separate beaker for the 10 ml.0090

You can even use less, you could probably get by with just a few ml of hydrochloric acid and this phenolphthalein.0095

The hydrochloric acid, you are going to use just a few drops, midway through the lab.0103

The phenolphthalein is what is known as a base indicator.0108

I will tell you more about that, later on in the explanation.0112

A pipette, you probably would need two pipettes or medicine droppers0115

because you are going to be putting a base, an alkaline solution, drop by drop into one of beakers.0120

You are also going to put HCl, an acid, into that same beaker eventually.0127

You do not have to clean the pipette every time between going from acid to base.0132

You do not want contaminate the inside of the pipette, that will affect what you are putting in at that time.0136

Having one pipette for basic solutions and one pipette or medicine dropper for acidic, it is probably a wise idea.0141

Drinking straw, you are not actually going to be drinking out of it, but you will be exhaling through it.0148

A clock or watch, a way that you can measure the time, you just need it for 1 minute.0153

Time required, about 30 minutes is all you need.0159

Part 1, before we begin, you got to make sure you are using gloves and goggles, safety first.0163

Because, even though these are very dilute substances, if they splash on your eyes, in your mouth,0169

if you get them on your hands and put your hands in your mouth, it is not a good thing.0179

Make sure that you are protecting yourself, you would actually replicate this lab and0182

do with the supervision of a teacher or professor.0186

Part 1, put water in the larger beaker, NaOH or sodium hydroxide in the small one.0189

You are going to use the drinking straw which you are not actually going to drink out of,0194

to exhale into the beaker with water for 1 minute straight, with every breath.0197

Here is what I mean, when the time starts, you are going to have your little beaker there.0205

If you notice, I was inhaling through my nose and exhaling through my mouth, that is what I mean by every breath.0220

Make sure that every breath, you are not actually exhaling with your nose, you are exhaling through your mouth.0224

Part of the inhaling through the nose is just to prevent you from inhaling any liquid.0229

Part of that is do not submerge the straw into the liquid.0235

For this first part in the beaker, there is just distilled water.0239

If the beaker is not very clean, there could be some remnants of other chemicals from previous labs.0245

Also, the reason why I’m saying not just emerge the straw is, at this time you might only accidentally inhale some water.0250

Later on in this lab, there are going to be other chemicals in that beaker.0257

There is going to be hydrochloric acid and sodium hydroxide, and phenolphthalein.0260

Things you do not want to swallow and get to your body.0263

Do not actually dip the straw on the water, just hover it over the liquid.0266

After you have exhaled all that CO₂ into the water, you are going to add one drop of that phenolphthalein to the water.0271

Phenolphthalein is a base indicator, meaning if a solution is on the alkaline part or basic part of PH scale,0281

it is going to turn to this color, this pinkish magenta color.0295

If it is acidic, it will actually be clear in this lab.0298

Once you get past to 7 on the PH scale, you are to see it turn to this color.0302

The more base you add, it will get darker and darker to a reddish even like light purple, if it gets really basic.0306

That is going to come in handy, in terms of measuring a change with the visual indicator in this lab.0317

The one drop of phenolphthalein is all you need.0325

If you put too much, the color change will happen to quick, for our purposes.0327

Just one drop is fine.0330

You are going to put NaOH, it is a base, into the water drop by drop until it becomes like this, until it turns to this color.0333

This is your endpoint that you are shooting for.0341

Maybe with that 1 mole, that particular concentration of NaOH, of sodium hydroxide,0344

maybe it is just 3 drops, that is all you need to get here, or maybe it is 6 in this lab.0350

It is going to be relative to the amount of acidity that is in the liquid.0356

If this is not really making sense yet, you are going to see at the other lab when we analyze what has happened here.0361

I will draw that for you, in terms of what happened.0367

You want to record the amount of drops of NaOH that it took do this, whether it was 3 drops of NaOH,0370

or maybe 7 drops of NaOH, it really depends.0379

Part 2, before we move on to the next part involving exercise, you want to get the solution back to neutral, where it was before.0386

Instead of dumping out all the stuff and having to put more water in and another drop of phenolphthalein,0394

you can add HCl, dilute hydrochloric acid drop by drop.0398

You might just need 1 drop, possibly.0403

You add 1 drop in, give it a little swirl so you can spread the HCl all through out.0410

If it turns clear, you are done, it is back to neutral, barely neutral.0414

You have just made that pinkish magenta go away, but you might need 2 drops, maybe even 3.0419

Do not put too much in because then you will get it into the acidic part.0425

You want to get as close to neutral as possible, we are back to our starting point.0429

Water is neutral.0432

That is your why, in terms of getting us back to neutral.0435

This is the fun part, you go run, play, exercise, jumping jacks, pushups, running in place, whatever, for 5 minutes straight.0446

Students involved in physical activity on a weekly basis, sports, running, jogging, exercising, it is not too much to ask.0456

But some people will be leaving after what 1 or 2 minutes.0463

Do your best, the point is to get your heart rate up, to get that breath rate up.0467

To do consistent cardiovascular work is going to make a difference, in terms of our data in the second half of this lab.0472

Once they are done with that, return immediately to redo the exhaling into the straw.0479

Add the NaOH again drop by drop.0483

You are just going to repeat part 1 again.0485

You are probably going to be exhaling more vigorously, make sure you are not submerging the straw into liquid0492

because now we have some other stuff in there, the phenolphthalein, NaOH, HCl.0497

What you get for 1 minute exhaling CO₂ within that water, shoot for the same endpoint,0503

meaning try to get the same exact pink or magenta color with the amount of drops you put in.0509

It will probably take a different amount of drops this time, that is the whole point.0517

The difference in the amount of drops is because there is a difference in CO₂ that you exhaled into the water.0520

You actually made water more acidic the second time, after exercising.0528

It is going to take more of the base to get the solution back into the basic side of the pH scale.0532

I’m going to draw that for you on the next slide, do not worry if it is still not making sense.0541

Here is a gentleman, presumably engaging in a marathon, definitely doing some cardiovascular exercise.0545

Here is some analysis, with the pH scale here is a 7, water is there.0553

We are going to say that at the right side here is basic, all the way to 14.0564

The right side is acidic going to 1 or 0.0579

There is a summary of the pH scale.0589

What we did here is we start out with water, and then what do we do?0596

We exhaled CO₂, it turns out that with CO₂ going into the water, you end up making a molecule called H₂CO₃, carbonic acid.0601

It is an acidic thing, when CO₂ combines with water which is actually neutral.0611

The more CO₂ you exhale, the more acidic it becomes.0615

As you are exhaling, it gradually creeps into this range.0619

Having much CO₂, let us say you got it to that point, whatever number happened to be on the pH scale.0628

That is going to be proportional to the amount of NaOH that you have to put in to get this point.0636

Here is that NaOH that you add drop by drop, after exhaling.0644

Once it gets just to the right of 7, 7.1, 7.2, 7.3, it will start to turn that pinkish,0650

that magenta color because of the phenolphthalein.0657

This amount of NaOH, maybe it is 6 drops, it is related to the amount of CO₂ that you exhaled off first time.0660

Let us say for trial 2, where you are exhaling a lot more, maybe after physical exercise, it goes to there.0668

That would mean that, it is going to take even more NaOH to get back to that same endpoint for trial 2.0680

Just comparing the amount of drops in trial 1 and the amount of drops of NaOH in trial 20690

is proportional to the amount of acidity that you put in that water.0695

Thanks to the CO₂ that you are exhaling.0699

This also applies to your bloodstream, in terms of how it works.0701

Here is a great picture of your lungs, arteries, and veins, all those blood flow to your lungs, your heart, your diaphragm down here.0704

In terms of CO₂ exiting your cells as a waste product of metabolism, it ends up making carbonic acid in your bloodstream.0713

You actually have chemoreceptors, little sensitive cells in the walls of arteries0724

that actually measure how acidic your blood is getting.0731

When it gets a little bit more acidic, it stimulates your breathing.0733

You do not have to think to breath, thankfully.0738

When we are asleep, we definitely are not consciously thinking about breathing.0741

When you are awake, you can decide to inhale and exhale when you choose.0745

It just happens automatically.0749

Every few seconds, typically, your blood gets this buildup of acidity,0751

thanks to all that CO₂ entering your bloodstream, and combining with water to make it more acidic.0756

And then, that will trigger your brain to stimulate your muscles, your diaphragm,0763

and the intercostal muscles in your rib cage region, to inhale some oxygen and get out that CO₂ from the bloodstream.0767

Your blood will go back to that more basic kind of standard or kind of default, you could say.0777

What happens as that cycle, from slightly more acidic to getting that CO₂ out of your body.0786

That is a part of the mechanism of you regulating breathing.0794

The connection to aerobic respiration which I already hinted at, is that aerobic respiration occurs in cells,0799

CO₂ is produce as a waste product of aerobic respiration.0804

The more ATP that is needed, how to exercise.0809

In this lab, when you are running in place or doing jumping jacks or sit ups, jogging, whatever you are doing,0813

as part of trial 2, you needed to do more glycolysis, more Kreb cycles in your muscles,0820

and more oxidated phosphorelation, including electron transport chain, to get more ATP.0827

This increases the CO₂ as well, the main place where it come from is your Kreb’s cycle.0834

That is going to be responsible for you having to exhale more.0841

Your breath rate goes up when you exercise because you need to have your heart beating faster.0844

But also, the need for oxygen and the need to get rid of CO₂ increases, with that increased activity.0849

The number of exhalations has a lot to do with this lab, in terms of the difference in NaOH,0857

the base that you have put in trial 1 versus trial 2, to get it back to that magenta color.0864

Thank your mitochondria for doing what you do.0869

Thank you for watching