Baking soda and vinegar

[deleted-71447]

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. . . 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. . . .
Thanks all of you for the terrific feedback, really, it's been most helpful.
Sherri

Hi lil bit,
The inverted container setup I was describing is the same one that zzzdoc described, where the mouth of the container (and the end of the tube) is submerged. I guarantee it will work if assembled properly. I have used laboratory versions for small scale models of flowing aquifers and for generation of acetylene.

Rather than try to weight the CO2 in the baloon, it will be easier and more accurate to weigh the vinegar and baking soda before and after the reaction, and then, from the difference, calculate the mass of CO2 generated. Because the density of CO2 is close to the density of the atmosphere, there will be a large buoyancy effect if you trying to measure its weight. For example, you could easily weigh 1-kg of liquid helium. If you let that liquid helium boil into vapor and capture it all in a large baloon, the baloon would float. The measured weight would obviously change, even though the mass is identical (same number of atoms). This results from the difference between mass and weight, which is easily overlooked for objects with relatively high density (like vinegar and baking soda), but becomes tricky when dealing with gases at the earths surface.

Sounds like you are down to the wire. Good luck!

[lil bit]

ZZZZ Doc and ChrisG do you think I could use large soda bottles and put the hole in the side instead of glass jars?

[Louise]

ZZZZ Doc and ChrisG do you think I could use large soda bottles and put the hole in the side instead of glass jars?

I think as long as the bottles are rigid and strong, you can use plastic. You just want something sturdy that won't deform/change shape.


Louise

[deleted-71447]

ZZZZ Doc and ChrisG do you think I could use large soda bottles and put the hole in the side instead of glass jars?

Yes, as Louise said, plastic should work. For small mouth containers, my idea of inserting a small cup of vinegar probably won't work, so you will need to figure out some other way to start the reaction after you have firmly screwed on the cap (so that you won't lose any CO2).

[Louise]

The measured weight would obviously change, even though the mass is identical (same number of atoms). This results from the difference between mass and weight, which is easily overlooked for objects with relatively high density (like vinegar and baking soda), but becomes tricky when dealing with gases at the earths surface.

Not to be too nitpicky, but the technical difficulty with weighing a vessel of gas is that many gases are less dense than air, not that you are measuring a gas. [I know you know that Chris... but other folks browse these threads]

Secondly, weight is a confusing term- as it can be defined as mass or a force (the force a mass experiences in a gravitational field). It appears that you are using a definition where it is a net force of gravity and boyancy (which as you point out is not an issue for most things we weigh), which is not one with which I am familiar, though it seems like different fields abuse the term in their own special way. I generally use the mass definitition, which is the most common way it is used. Usually, at this point, I'd whip out my NIST handbook on the SI system[1], but I think it that would be overkill.


Louise
[1] A great reference which can be found at:
http://physics.nist.gov/Pubs/SP811/sp811.html

They used to mail out copies to anyone who asked, but I guess they don't do that in the internet age.

[deleted-71576]

You could drill two holes in the cap of the bottle. I've done this with a Diet Coke and Mentos science experiment. A little tricky, but doable. Hobby stores have brass tubing that is small enough to work with this.

[lil bit]

Chris I like the idea of weighing it all together if there will be a noticeable weight change. I do have access to a triple beam scale. Louise, I dont' think I understood a thing you said in that last response.
I have to say this entire dialogue has been really terrific. I appreciate the three of you sticking with me here on this Louise, Chris, and zzzzdoc.
TThanks,
Sherri

[deleted-71447]

lil bit, I'm glad this discussion has been helpful. Please keep checking in if you run into problems, and, if not, please let us know how it turns out!

Not to be too nitpicky, but the technical difficulty with weighing a vessel of gas is that many gases are less dense than air, not that you are measuring a gas. [I know you know that Chris... but other folks browse these threads]

Secondly, weight is a confusing term- as it can be defined as mass or a force (the force a mass experiences in a gravitational field). . .

Louise, thanks for catching my sloppy use of the word "weight" in reference to measured versus actual values. As we both initially mentioned, the problem is really related to buoyancy and the actual (as opposed to measured) weight of an object, is not affected by buoyancy. While we're nitpicking, I'll point out that the technical difficulty of weighing a gas does not depend on whether the gas is lighter or heavier than air. The buoyancy effect is significant in either case. For a clear explanation, the section on "true mass" on this web page is pretty good:
http://www.npl.co.uk/mass/faqs/buoyancy.html
The guts of the issue are here:
BC = (V1 - V2) × pair
where BC is the buoyancy correction to be applied
V1 is the volume of artefact one (ie M1 / pM1)
V2 is the volume of artefact two (ie M2 / pM2)
pair is the density of the air at the time of comparison

Here is an example calculation for the case of trying to weigh some CO2 in a container: If we use a balance to weigh a liter of CO2 with a density of 2g/L in a 50g container, V1 would be about 1L, and V2 would be about 0.007L (assuming we use an iron counterbalance). The density of air is about 1.2 g/L, so the buoyancy correction would be (1-0.007)*1.2=1.19g. In this case, the 52g of container and CO2 on the balance would register as 50.81g. Our balance would tell us that the mass of CO2 in the container is only 0.81g, while it is actually 2g.

Bottom line: If we weigh uncompressed gas on a standard balance, the balance will not report the actual mass (or weight!).

[deleted-71576]

We do it easier in medicine - "In with the good air, out with the bad air." And the artifact is always someone else's fault.

Actually, we just measure flows and concentrations directly.

[Louise]

lil bit, I'm glad this discussion has been helpful. Please keep checking in if you run into problems, and, if not, please let us know how it turns out!

Not to be too nitpicky, but the technical difficulty with weighing a vessel of gas is that many gases are less dense than air, not that you are measuring a gas. [I know you know that Chris... but other folks browse these threads]

Secondly, weight is a confusing term- as it can be defined as mass or a force (the force a mass experiences in a gravitational field). . .

Louise, thanks for catching my sloppy use of the word "weight" in reference to measured versus actual values. As we both initially mentioned, the problem is really related to buoyancy and the actual (as opposed to measured) weight of an object, is not affected by buoyancy. While we're nitpicking, I'll point out that the technical difficulty of weighing a gas does not depend on whether the gas is lighter or heavier than air. The buoyancy effect is significant in either case. For a clear explanation, the section on "true mass" on this web page is pretty good:
http://www.npl.co.uk/mass/faqs/buoyancy.html
The guts of the issue are here:
BC = (V1 - V2) × pair
where BC is the buoyancy correction to be applied
V1 is the volume of artefact one (ie M1 / pM1)
V2 is the volume of artefact two (ie M2 / pM2)
pair is the density of the air at the time of comparison

Here is an example calculation for the case of trying to weigh some CO2 in a container: If we use a balance to weigh a liter of CO2 with a density of 2g/L in a 50g container, V1 would be about 1L, and V2 would be about 0.007L (assuming we use an iron counterbalance). The density of air is about 1.2 g/L, so the buoyancy correction would be (1-0.007)*1.2=1.19g. In this case, the 52g of container and CO2 on the balance would register as 50.81g. Our balance would tell us that the mass of CO2 in the container is only 0.81g, while it is actually 2g.

Bottom line: If we weigh uncompressed gas on a standard balance, the balance will not report the actual mass (or weight!).

Thanks for the expanded discussion and the examples. I was thinking of the physical act of measuring when I mentioned density (and I'll happily invoke zzzzdoc's "the artifact is always someone else's fault" as the explanation for getthing the wrong mass. Stupid air- complicating everything!). I was imaging giving the gas a high density through compression, so that it was "sufficiently dense" to act like a "normal" solid. Though, I see from the site you provided that I should be doing boyancy corrections for solids too, which is something I never thought of. This is a nice example of where certain approximations are made, and they meshed with our understanding of the way the world works (I don't float!), that you would never notice that the assumptions are there, unless you get in a discussion like this.

lil bit: Sorry if the discussion has veered toward the obscure. As you probably gathered, measuring gas is hard! Measuring it correctly is even harder! Chris and I were using the term “weight� to mean different things (both of which are proper usages), so I just wanted to point that out. This is actually a very interesting problem to think about, because effects that we normally don’t consider important suddenly become important. If you want clarification on anything I've said, feel free to ask, though it isn't really important to your experiment.

Louise

[lil bit]

I'm sorry but I don't understand what you are all talking about with regards to the weight of CO2. Bottom line, can we weigh the result as zzzzdoc suggested with evrything on the scale, the bottle with the baking soda, vinegar and balloon. Will there be a difference and will it be consistent????

[lil bit]

I'm sorry, it was Chris G who suggested weighing the vinegar and baking soda before and after the reaction. Would this be with or without the balloon?

[Louise]

I'm sorry, it was Chris G who suggested weighing the vinegar and baking soda before and after the reaction. Would this be with or without the balloon?

You would weigh the baking soda and vinegar and all the containers before you start [without the balloon]

You would weigh the baking soda and vinegar and all the containers after you do the reaction. [Without the Co2 in the ballon.]

The difference between the two should be the mass of Co2 produced. Since this involves only weighing solid things and not gas you don't need to worry about boyancy and the meaning of "weight" and all the complicated things Chris and I were talking about. The ONLY question is whether you can measure a small mass change well. As I mentioned somewhere above, one liter of the gas is about 0.05 oz. So, can you measure a change that small accuractely with your scale?

I don't know how much gas you get, but I am guessing it is two liters or less. [How much did you get when you tried measuring the volume of the balloons? ]

Hopefully, that was clear... and I managed not to get distracted in to philosphocal matters.


How much baking soda and vinegar do you use?
Louise

[deleted-71447]

Hi Lil bit,
Sorry for the confusion. Louise has probably answered your questions about the procedure that I suggested.

The bottom line about trying to weigh the CO2 in a balloon is that you would need to make a mathematical correction. Details of that correction are in my previous post. The math would probably be appropriate for a bright elementary school student, but the concepts can be confusing. It might make a nice science project for another year!

[lil bit]

Louise, zzzzdoc and ChrisG, I was talking with another parent who is also a scientist and he suggested measuring the volume of the balloon by placing the balloon in a container and filling it with flour and then measuring the flour. This is assuming the balloons are consistent for which we need to do a few trials to determine. It sure solves the problem with the water. What do you think???
I will keep you updated and let you know how it turns out.
Thanks,

[Louise]

Louise, zzzzdoc and ChrisG, I was talking with another parent who is also a scientist and he suggested measuring the volume of the balloon by placing the balloon in a container and filling it with flour and then measuring the flour. This is assuming the balloons are consistent for which we need to do a few trials to determine. It sure solves the problem with the water. What do you think???
I will keep you updated and let you know how it turns out.
Thanks,

As someone who bakes, I think that will be a problem. Flour can pack very well (small volume) or not well (large volume). Think to all those recipes that call for "sifted cup" or a "unsifted cup" of flour. (Or if you've filled a container then tapped it a couple of times and found you have more space) The volume of flour is very variable. This is why many chefs weigh the flour instead of using volume (measuring cups). So, I think you will have as much variabilty as with the water method. Other solids (sugar/salt/etc) have the same problem, because packing (how the chunks fill up the space) is a major issue.

Louise

[lil bit]

OOPS your right. I was so excited about the idea that I didn't think about that and I do alot of baking as well. Oh well, it seemed like a good solution. Thanks for pointing that out.
Sherri

[lil bit]

Louise, zzzzdoc, and ChrisG,
We borrowed a triple beam balance from school. We did a few trial runs
using ChrisG's idea to weigh everything before and after. It worked!!!!
We did a two trials with white vinegar and got a difference of 1.6 and 1.7
grams. YEAHHH!!!
Thank you!
lil bit

We did measure the results from 2 balloons as well and their weights came back .9 and .8 grams. A difference between the two methods for sure. I assume the difference has to do with what you all were talking about before.
Well, I'm glad we can get started on this experiment . We'll keep you posted as to the results.
Thanks
Sherri

[Louise]

Louise, zzzzdoc, and ChrisG,
We borrowed a triple beam balance from school. We did a few trial runs
using ChrisG's idea to weigh everything before and after. It worked!!!!
We did a two trials with white vinegar and got a difference of 1.6 and 1.7
grams. YEAHHH!!!
Thank you!
lil bit

We did measure the results from 2 balloons as well and their weights came back .9 and .8 grams. A difference between the two methods for sure. I assume the difference has to do with what you all were talking about before.
Well, I'm glad we can get started on this experiment . We'll keep you posted as to the results.
Thanks
Sherri

Very nice! Glad Chris's idea worked.


Louise

[deleted-71447]

Thanks for keeping us posted and congrats on getting some results!

[lil bit]

We finally got done. We averaged the results together ( can we do that/)
We did five trials of each vinegar. White vinegar weighed 1.85 grams on average; red wine vinegar weighed 1.65 grams on average; and apple cider vinegar weighed 1.69 on average. Does this mean that the white vinegar had a larger reaction or is the difference not big enough to know???
Also, could you explain to me how measuring the stuff after the reaction gives me a measurement of the carbon dioxide???
It was hard to measure the vinegar so each trial started with a different weight. Does this make a difference???

Thanks,
lil bit

[Louise]

We finally got done. We averaged the results together ( can we do that/)
We did five trials of each vinegar. White vinegar weighed 1.85 grams on average; red wine vinegar weighed 1.65 grams on average; and apple cider vinegar weighed 1.69 on average. Does this mean that the white vinegar had a larger reaction or is the difference not big enough to know???
Also, could you explain to me how measuring the stuff after the reaction gives me a measurement of the carbon dioxide???
It was hard to measure the vinegar so each trial started with a different weight. Does this make a difference???

Thanks,
lil bit

You can average each of the 5 trials for a type of vinegar. Not only is that fine, but it is the way you should do it.

You should check the acidity of each type of vingear... the results may track with the acidity.

As for the vinegar weight... well, technically it should be a controlled variable. How much did the weight (or volume vary)? The true answer is that is depends on whether the baking soda or the vingear is the limiting reagent. Here is a really crude analogy. You are baking muffins and you have a huge batch of batter, but only 1 muffin tin (and no one to wash it). So, you can only make 12 muffins and you end up with a gallon of raw batter left. In this case, it doesn't matter if you started with one gallon of batter, or 5 gallons of batter, because the muffin tin is what stops production. You might have the reverse case, where you had 500 muffin tins. Then, the amount of batter might very well limit your production.

So, the acid in the vinegar and the baking soda reacted in a certain way. If you have a ton extra vinegar, then the weight differences don't matter because what is stopping production is the amount of baking soda.


As for why this method works- here is a very crude explanation. You see two things at the start (baking soda and vinegar), and three things at the end (baking soda and vinegar and gas). This isn't really right. You don't really have baking soda or vinegar in the end, because they have been used up to make carbon dioxide (you have new chemicals that you have created). So, you can think of it like this.
At the beginning you are weighing the carbon dioxide! It is just trapped in the baking soda and the vinegar (in a different chemical form, and as a solid too). After the reaction, the carbon dioxide has escaped, because it is a gas. So, you weigh everything but the carbon dioxide. So the subtraction gives you only the carbon dioxide.

Makes sense?

Louise

[deleted-71588]

We averaged the results together ( can we do that?)...It was hard to measure the vinegar so each trial started with a different weight.

Well you did it (averaged the results). Given that you didn't control the starting weight, scientifically it is worthless. As long as you have the individual starting and ending weights of each trial, all is not lost. If you convert the change on each individual trial to a percentage of the original starting weight, you get a "normalized" result. An average of these percentages makes scientific sense because you have mathmatically eliminated the uncontrolled variance (the starting weight of the vinegar).

The above assumes that there was an excess of baking soda in all of the tests. If on the other hand, there was an excess of Acetic Acid, then the starting weight difference of the vinegar didn't matter.

Given that you saw an average difference between the white and red vinegar, I'm guessing that you had an excess of baking soda in at least some of the tests.

Does this mean that the white vinegar had a larger reaction or is the difference not big enough to know???

We can't help you answer that without knowing what the individual data was and normalizing it. Then if the difference (variance) of each white vinegar tests plus the difference (variance) of the red wine tests was less than the difference between the normalized means, you definitely have something statistically significant. If it is close, then you need to look up statistical significance tests.

Also, could you explain to me how measuring the stuff after the reaction gives me a measurement of the carbon dioxide???

This is based on a conservation of matter principle. If you account for the weight of everything going into the reaction, it should equal the weight of everything coming out of the reaction. You measured everything going in, you measured everything but the gasses coming out; therefore, the difference is the weight of the gasses. Because we know the chemical reaction involved, we know the most significant gas product is CO2, this method is choosing to ignore any evaporation that might have happened to cause a water vapor gas component.

Note: If you had captured and weighed all of the gas products (a difficult thing to do), you would also be lumping any water vapor in with the CO2.

[Louise]

Well you did it (averaged the results). Given that you didn't control the starting weight, scientifically it is worthless.
[\quote]

Well, we really have no idea what the variation was on a percent scale, so it is hard to say if this is problematic.

As long as you have the individual starting and ending weights of each trial, all is not lost. If you convert the change on each individual trial to a percentage of the original starting weight, you get a "normalized" result. An average of these percentages makes scientific sense because you have mathmatically eliminated the uncontrolled variance (the starting weight of the vinegar).

A good idea, as are your statistical tests suggested below, but I think this is a project being done by a fairly young child. I think mathematical fixes are going to consume massive mom/dad-hours and not really help the student all that much. No judge is going to expect a 3rd grader to have normalized the data and run statistical test...

The above assumes that there was an excess of baking soda in all of the tests. If on the other hand, there was an excess of Acetic Acid, then the starting weight difference of the vinegar didn't matter.

Right, the limiting reagent is the key.

Does this mean that the white vinegar had a larger reaction or is the difference not big enough to know???
We can't help you answer that without knowing what the individual data was and normalizing it. Then if the difference (variance) of each white vinegar tests plus the difference (variance) of the red wine tests was less than the difference between the normalized means, you definitely have something statistically significant. If it is close, then you need to look up statistical significance tests.

Again, I think this depends very much on the age of the student. Certainly a 12th grader could be doing this project and you would expect a bit more rigor in the control of initial conditions and post-data analysis, but a primary school child probably wouldn't/couldn't/shouldn't do this. Middle school, it could go either way.

Lil Bit: If you could post your raw data, for one type of vinegar (starting masses of the components, ending masses, etc.) we can take a quick look at the standard deviations of the normalized weights.

Louise

[deleted-71588]

Sorry, I wish the grade level showed up somewhere. I didn't realize this was a second grade effort. I was confused by the detour this thread took into bouyancy and measuring gasses.

Post the raw starting and ending weights by trial and I'll be glad to do the number crunching.

[lil bit]

What we did is measure out 50ml of each vinegar and mixed it with 2 1/2 tsp of baking soda. We used more than enough baking soda so as to have some left over. We even measured the time, 10 minutes for each trial, before measuring the after product. What was difficult to control was the amount of vinegar and the pre-weight changed each time. We considiered weighing the vinegar but then we couldn't control for it's mass as there is the possibility that each vinegar might have a different weight. The white vinegar had the largest output. We think this might reflect the impurities or other components in the apple cider and red wine vinegar which would suggest that there was more acid in the white vinegar than in the other two.
Sherri (mom)

[lil bit]

Craig,
I took the difference from each trial and divided it by the begining weight. I then averaged those percentages and what I got is 2.136% for white vinegar; 1.884% for red wine vinegar; and 1.95% for apple cider vinegar. Is this what you suggested and does this difference mean anything.
Sherri

[Louise]

What we did is measure out 50ml of each vinegar and mixed it with 2 1/2 tsp of baking soda.

I think this is good. As long as you always used 50 mL, I think you are good to go in terms of controlling that variable.

I think your variations are due to variation in weighing, not variations in the acid power. If you have excel, you can calculate the standard deviation of the weights. For example, if you measured 1.85 +/- 0.2 grams over your 5 trials, then there isn't a difference in your results. If you post the raw numbers here, either Craig or I can calculate the standard deviation.

Here is some information about vinegar.
"The strength of vinegar is measured by the percent of acetic acid present in the product. All vinegar sold in the United States at the retail level should be at least 4% acidity as mandated by the U.S. Food & Drug Administration (FDA). Typical white distilled vinegar is at least 4% acidity and not more than 7%. Cider and wine vinegars are typically slightly more acidic with approximately 5-6% acidity"

We considiered weighing the vinegar but then we couldn't control for it's mass as there is the possibility that each vinegar might have a different weight.

This is something to worry about, but scientists and engineers generally like mass, because we can convert it to any other quantity. In the case of vinegar, it is mostly water, and they all have the same density (to the level you can measure it), so mass would have been okay. But, if you measured 50 mL every time, that is okay too.

We think this might reflect the impurities or other components in the apple cider and red wine vinegar which would suggest that there was more acid in the white vinegar than in the other two.

See above about acidity- but it should also be printed on the bottle as well.

So, did you daughter have fun? As you have found out, even "trivial" experiments have a lot of complexity, but hopefully watching the reactions bubble away was enjoyable.

If you have any questions still remaining, please post back, and we will do our best to explain them with out getting too technical. If your found any of our explanations really clear, it might be worth telling us too, since we are never sure how best to explain things.

Louise

[deleted-71588]

Sherri, given that you had an excess of baking soda in each run, you did a very appropriate normalization to make the averages scientifically meaningful!

Now for the statistical significance part. If the normalized ranges high to low of the white vinegar tests don't overlap the apple cider high to low range and those don't overlap the red wine vinegar, then you definitely have statistically significant results! No need to do the math. Easy enough to be able to explain that no overlapping results means they were all good runs.

If there is some overlap, then applying some math testing is appropriate if this were a higher grade level.

[lil bit]

Louise,
These are the outcomes:
white vinegar: 1.8; 1.9; 1.75; 2.0; 1.8
red wine vinegar: 1.8; 1.7; 1.6; 1.7; 1.55
apple cider vinegar: 1.75; 1.7; 1.75; 1.7; 1.55
Thet were all 5% acidity