Baking soda and vinegar

lil bit · Post by **lil bit** » Mon Feb 19, 2007 2:45 pm

My daughter is doing an experiment comparing the reaction of different vinegars, all with the same acidity, by capturing the reaction in a balloon. We had planned to measure the volume of the balloon by submerging it in water tied to a weight. The problem is the balloon stretches and stays partially above water. Can you suggest any other way of measuring the volume of the carbon dioxide??? Thank you

MelissaB · Post by **MelissaB** » Mon Feb 19, 2007 4:00 pm

Can you fill the container you're using to measure volume with water, upend it in a bigger container of water (make sure there's no air in the measurement container) and then let the air in the baloon out underneath the lip of the measurement container so the carbon dioxide goes into it, displacing the water already there? You'd need to be careful not to let any of the carbon dioxide 'escape' the measurement container, but it should work!

lil bit · Post by **lil bit** » Mon Feb 19, 2007 7:12 pm

Melissa, thank you for responding but I have no idea how to do what you've suggested. How would you upend one container of water into another? And, how do you let the air out of the balloon?

zzzzdoc · Post by **zzzzdoc** » Mon Feb 19, 2007 7:41 pm

Imagine a large bin of water. Fill the water close to the top, but leave a little room so that it doesn't overflow. Take something like a graduated cylinder, and fill it totally with water. Take a piece of cardboard and cover over the top of the graduated cylinder and turn it upside down in the water. Remove the cardboard. The graduated cylinder should be totally underwater with no air in it.
Now, take the full balloon, put it under water so that the opening is directly under / in the bottom of the graduated cylinder. Release the balloon, and the CO2 will rise to the top of the graduated cylinder, displacing a volume. Measure the volume of the gas, and there you have it.

lil bit · Post by **lil bit** » Tue Feb 20, 2007 8:46 am

Thank You.

lil bit · Post by **lil bit** » Mon Mar 05, 2007 7:12 pm

We have found that the balloons don't work for measuring the output of carbon dioxide by volume. Is there another way to measure the output either with a balloon or something else???
Thank You

Louise · Post by **Louise** » Mon Mar 05, 2007 7:20 pm

lil bit wrote:We have found that the balloons don't work for measuring the output of carbon dioxide by volume. Is there another way to measure the output either with a balloon or something else???
Thank You

Why don't they work? Does the carbon dioxide leak out, is the volume too big, etc? T

Louise

lil bit · Post by **lil bit** » Mon Mar 05, 2007 7:56 pm

Louise thank you for responding.
I couldn't figure out a way to do the prior suggestion and keep it constant. I did come up with an alternative method for measuring the volume but it wasn't reliable. We then did a couple of trials just to check the reliability of the balloons and they too weren't reliable. We got two different sizes with the same vinegar. Someone suggested weighing the balloon before and after as the stretchiness of the balloon wouldn't matter. I'm not sure I can get access to a scale and I don't know if the weight will be significant enought to do it this way. This is my daughter's first experiment. She is in third grade. We have spent many hours working on this and she has written alot of pages in her journal. It has been alot of fun and she has learned alot but I don't know how we will be able to complete the experiment. Any suggestions????
Thanks, Sherri

zzzzdoc · Post by **zzzzdoc** » Mon Mar 05, 2007 8:14 pm

You should re-look at the suggestion I made earlier. It should work as an easy way to measure the volume in the balloon.

lil bit · Post by **lil bit** » Mon Mar 05, 2007 8:52 pm

It doesn't look at all easy though it does seem like a good idea.. First we have to find a bin large enough to submerge a cylinder and a cylinder large enough to hold a balloon. The bin also has to be large enough to hold my arms. As for the balloon, if you put the tip under the cylinder you would need to press down hard enough to keep the balloon from escaping in which case the air couldn't be released and if you loosten it the balloon will escape. We have spent alot of time and thought on this. I think we may be ready to move onto something other than water with which to measure the volume. Any other suggestions????
Thanks

ChrisG · Post by **ChrisG** » Mon Mar 05, 2007 9:32 pm

lil bit,
The method that will work best for you depends on the resources that are available to you. If I were in your shoes, I would make a little reaction chamber out of a glass jar with a air tight lid (like a wide mouth mason jar), a drill, a glue gun, and a piece of flexible tubing. The construction would be something like this:
- Drill a hole (slightly smaller than the outer diameter of the flexible tube) through the top of the jar's lid.
- Squeeze the flexible tube through the hole. Apply hot glue to both sides of the lid where the tube contacts the lid so that the seal between the lid and tube is airtight.
- To test that the seal is air tight, screw the lid onto the jar, put soapy water around the seal, and then blow into the tube. If you see soap bubbles coming out of the seal, you have a leak.

To run the experiment, I would
1) wash and dry the jar
2) put the baking soda in the jar.
3) put the vinegar into a small plastic cup and carefully (without spilling any) set the cup inside the jar.
4) Screw on the lid, without upsetting the cup of vinegar.
5) Place the end of the tube under an inverted, water filled container (as described by zzzdoc).
6) tilt or shake the jar until the cup of vinegar tips and mixes with the baking soda.
7) Capture the exhaust in the inverted container. If there is too much exhaust to be captured, use a bigger container to capture the exhaust or add less baking soda.

I expect this would be more accurate than trying to fill balloons. Also it should be easier to use the inverted, water filled container if you don't have to hold the end of a balloon in the water.

Good luck!

zzzzdoc · Post by **zzzzdoc** » Mon Mar 05, 2007 11:08 pm

Or, to expand on what Chris is saying, if you don't want to use an inverted tube at all, you could have the tubing from the first tube go into a second bottle through a hole that exits at the top of the second mason jar. Drill a second hole in the second mason jar and insert a tube that goes all the way to the bottom of the jar. Fill the second mason jar all the way to the top with water. Put the outer portion of that second tube in a normal,empty, graduated cylinder. As the CO2 is released from the first mason jar it will go into the top of the second mason jar, pushing water out the second tube into the graduated cylinder. The volume of water pushed out of the second jar is the same volume as the gas produced, which you can directly read off the graduated cylinder (assuming no effects of dissolved CO2, etc). You could also measure the volume of CO2 in the second mason jar but that would require you to make inverted volume markings on it.

I'm not able to make a drawing of this right now, but a setup with a sealed glass vessel with 2 tubes in it (one short and one long) is a very standard setup which you should be able to find in many places on the internet. Its the same theory as a Super Soaker water pistol, except that is allowed to pressurize instead of flowing freely.

I hope you can understand that explanation, but, with a little building, it's another solution to the problem.

Louise · Post by **Louise** » Tue Mar 06, 2007 7:10 am

lil bit wrote:Louise thank you for responding.
I couldn't figure out a way to do the prior suggestion and keep it constant. I did come up with an alternative method for measuring the volume but it wasn't reliable. We then did a couple of trials just to check the reliability of the balloons and they too weren't reliable. We got two different sizes with the same vinegar. Someone suggested weighing the balloon before and after as the stretchiness of the balloon wouldn't matter. I'm not sure I can get access to a scale and I don't know if the weight will be significant enought to do it this way. This is my daughter's first experiment. She is in third grade. We have spent many hours working on this and she has written alot of pages in her journal. It has been alot of fun and she has learned alot but I don't know how we will be able to complete the experiment. Any suggestions????
Thanks, Sherri

Well, the volumes may not actually be constant! There is both error in your measurement and variability in the amount of gas produced, and it can be difficult to figure out which is which. Measuring the volume of the ballon by volume of water displaced is the easiest method, I think. You can certainly rig more complicated setups to extract the gas from the balloon and use that to displace water as well. Chris and Alan's suggestiong for how to do this very detailed, and should work well.

I don't think a scale will work for the reasons you say.

People often use a bathtub as a large bin.

Louise

lil bit · Post by **lil bit** » Tue Mar 06, 2007 11:28 am

The bath tub is a great idea, I don't know why I didn't think about that.
I don't understand how you can invert a jar with a tube coming in from the bottom because the jar won't be flush with the bottom and I would think water would get in or out as would the gas. Am I missing something here?? I thought it was a great idea using the two jars though, thanks.
I might still try a scale. It's amazing really, we have spent so much time trying to figure this out, running tests...As far as measuring the balloons reliability, we did keep our measurements consistent. I assume the variability was due to differences in the balloons. My question is if we did measurements with a scale, would that balloon variability make a difference. In other words, is the weight of the carbon dioxide correlated with the size of the balloon or could you have two balloons, one smaller than the other but the weight would be the same.
We have spent so many hours trying to make the balloon in the water work and are running out of time I might want to try weighing them instead of getting the two jars working although it sounds really fun and a great learning experience about displacement.
Thanks all of you for the terrific feedback, really, it's been most helpful.
Sherri

Louise · Post by **Louise** » Tue Mar 06, 2007 12:29 pm

lil bit wrote:The bath tub is a great idea, I don't know why I didn't think about that.
I don't understand how you can invert a jar with a tube coming in from the bottom because the jar won't be flush with the bottom and I would think water would get in or out as would the gas. Am I missing something here?? I thought it was a great idea using the two jars though, thanks.
I might still try a scale. It's amazing really, we have spent so much time trying to figure this out, running tests...As far as measuring the balloons reliability, we did keep our measurements consistent. I assume the variability was due to differences in the balloons. My question is if we did measurements with a scale, would that balloon variability make a difference. In other words, is the weight of the carbon dioxide correlated with the size of the balloon or could you have two balloons, one smaller than the other but the weight would be the same.
We have spent so many hours trying to make the balloon in the water work and are running out of time I might want to try weighing them instead of getting the two jars working although it sounds really fun and a great learning experience about displacement.
Thanks all of you for the terrific feedback, really, it's been most helpful.
Sherri

Figuring out how to do the measurement right is the hardest part of the scientific process, I think.

1) The balloon will only be a different size if it has a different amount of gas in it. There may be balloon to balloon variations in thickness and weight, but in terms of the size the balloon expands to, the gas is the major contributor.

2) When I say "amount of gas", I mean the number of molecules of gas. The number of molecules of gas can take up more (or less) space (volume) depending on the temperature. So, if you do the measurement in warm water, and then in cold water, you will get different volumes. [This is why spray cans say not to heat them. As it gets hot, the volume gets bigger... then it explodes if it is in a rigid container. In a balloon, it would just stretch and get bigger]

3) Since you cannot count the molecules directly, you have to measure some other property instead. Mass and volume are both directly related to the number of molecules (at a given temperature).

4) The density of your gas is similar to air. That means that for 1 liter of gas (think a drink bottle to estimate the volume), the mass of the gas will be about 1 gram (or about 0.04 ounces). I don't think you have a scale that good! When you weigh the ballon plus gas, most of the mass will come from the ballon itself. You would need to weigh each ballon before filling, since they probably are not made so they have exactly the same weight.

Louise