Baking soda and vinegar

[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

[deleted-71588]

white red wine apple cider
1.8 1.8 1.75
1.9 1.7 1.7
1.75 1.6 1.75
2 1.7 1.7
1.8 1.55 1.55

1.850 1.670 1.690 Average
0.100 0.097 0.082 Std Dev
0.010 0.010 0.007 Variance

The averages don't match the normalized percentages you posted, so I'm guessing that the variation in the starting weights requires normalization.

[deleted-71588]

Sorry, lost the Excel spread sheet column spacing.

[lil bit]

I didn't post percentages but the actual weight differences for each trial.

[deleted-71588]

lil bit, can you post the starting weights for the trials?

[lil bit]

The starting weights for the white were:87.1; 86.7;86.15;86.6;86.6.
The starting weights for red were: 89.0; 89.8; 88.3; 87.7; 88.15.
The stareting weights for apple weer: 87.45; 86.4; 86.45; 86.3; 86.7.

[Louise]

The starting weights for the white were:87.1; 86.7;86.15;86.6;86.6.
The starting weights for red were: 89.0; 89.8; 88.3; 87.7; 88.15.
The stareting weights for apple weer: 87.45; 86.4; 86.45; 86.3; 86.7.

I recalculated the standard deviation using the normalization of the starting masses. So, for example, for the white vinegar trial, every thing ideally should weigh 87.1 g. So, the results for the 86.7 trial were 99.5% of what they should be, because the starting weight was only 99.5% of what is should be. (Which is really good- all the standard deviations on these are really fantastic. Obviously you took a lot of care in your measuring.)

The "norm factor" is the percent off the max weight. The "gas" is your experimental value. "norm gas" is the amount of gas you would have measured if you had used a standard weight. Mathematically, I used [(1-norm factor)*gas+ gas). Then I calculated the average and the standard deviation.

white norm factor gas norm gas
87.1 1 1.8 1.8
86.7 0.995407577 1.9 1.908725603
86.15 0.989092997 1.75 1.769087256
86.6 0.994259472 2 2.011481056 ave 1.859925373
86.6 0.994259472 1.8 1.810332951 std 0.099564815

red
89 0.991091314 1.8 1.816035635
89.8 1 1.7 1.7
88.3 0.983296214 1.6 1.626726058
87.7 0.976614699 1.7 1.739755011 ave 1.692199332
88.15 0.981625835 1.55 1.578479955 std 0.093376481

cider
87.45 1 1.75 1.75
86.4 0.987993139 1.7 1.720411664
86.45 0.988564894 1.75 1.770011435
86.3 0.986849628 1.75 1.77301315 ave 1.715345912
86.7 0.991423671 1.55 1.56329331 std 0.087550544

If you look, you see there is overlap between the normalized red and the white vinegar data. That is, 1.8, 1.7, 1.76 could appear in both groups. The standard deviation also says there is some overlap[1]. So, usually, you report the average + and - the standard deviation. So the range of values for the white vinegar based on your trial is 1.86 +/- 0.09, which means that you would believe numbers that were 1.76 to 1.96 (rounded). For red, 1.79 to 1.60 is the range. If you were a scientist, you would do more averages, and more sophisticated statistics to tell if these numbers are different or the same, since it looks "suggestive" that the white vinegar has a higher average value. But, with the data we have, since the ranges do overlap, I'd have to say the results are the same for all vinegars.

Given that this reaction should depend on the amount of acid and baking soda, you might expect that if all are 5% acid, and all are 50 mL, you should get the same result.

Louise

[1] from the wikipedia-
"The standard deviation is the most common measure of statistical dispersion, measuring how widely spread the values in a data set are. If the data points are close to the mean, then the standard deviation is small. Conversely, if many data points are far from the mean, then the standard deviation is large. If all the data values are equal, then the standard deviation is zero."

[deleted-71588]

I'm guessing that the variation in the starting weights requires normalization.

lil bit, Boy was I WRONG! You and your lab assistant did a FANTASTIC job of measuring!

I used Excel and normalized and graphed your data and am attempting to have the science buddies administrators forward it to you.

If you throw out the highest two trials from the white and the bottom two from the red, the rest of the data is in a very tight clump.

[deleted-71576]

I agree. Nice data.

[Louise]

I'm guessing that the variation in the starting weights requires normalization.

lil bit, Boy was I WRONG! You and your lab assistant did a FANTASTIC job of measuring!

I used Excel and normalized and graphed your data and am attempting to have the science buddies administrators forward it to you.

If you throw out the highest two trials from the white and the bottom two from the red, the rest of the data is in a very tight clump.

Not that you should throw out data... but I totally agree with Craig's main point about data quality. When I calculated the deviations I was very impressed. My data rarely looks this good!


Louise

[lil bit]

I'm not sure I follow about the normalization of the begininning weights but I calculated the standard deviation of the results by subtracting the average from each result, squaring the difference, adding the squares, dividing by 5 and getting the square root of that. A friend gave me the calcualtion. I got 1.85 +/- .089; 1.67 +/- .096 and 1.69 +/- .073. So white vinegar: 1.939 to 1.76
red vinegar: 1.766 to 1.574
apple cider: 1.76 to 1.62
We made a mistake on the intial average of the red wine results, it's 1.67 not 1.65. So does this show a difference or not???

[Louise]

I'm not sure I follow about the normalization of the begininning weights but I calculated the standard deviation of the results by subtracting the average from each result, squaring the difference, adding the squares, dividing by 5 and getting the square root of that. A friend gave me the calcualtion. I got 1.85 +/- .089; 1.67 +/- .096 and 1.69 +/- .073. So white vinegar: 1.939 to 1.76
red vinegar: 1.766 to 1.574
apple cider: 1.76 to 1.62
We made a mistake on the intial average of the red wine results, it's 1.67 not 1.65. So does this show a difference or not???

I think there is no difference between the vinegars. Your standard deviation calculation is fine. If you have microsoft excel they will do this calculation for you- "stdev(cells)", since this calculation is a pain.

However you look at the data (my corrections or your calculations), your standard deviations are very small. You can see my calculated "normalized" standard deviations are quite small. So, you get 1.85 +/- 0.089 if you don't correct the starting mass, and I get 1.8599 +/- 0.0996 (I put extra digits in, so you can find it in the table I posted... on the right hand side).

The normalization thing... So, if you assume for white vinegar that 87.1 g was the starting mass you wanted, then the second trial of 86.7 g was a bit too light. It is only 99.5% of the mass, instead of the whole mass. So, the result was "incorrect" by 99.5%. So, if I know that your measured 1.75 g is only 99.5% of the value, then I can calculate that 100% of the value should be 1.769 g. So, I did this for all trials. This removes all variations in the starting weight, and gives you a better idea of the "true" variations.

BUT, you measured your masses so accurately, that the few percent error from the starting mass variation hardly has an impact.

Louise

[deleted-71447]

Hi,
Maybe this question has already been answered, but do these weights include the mass of baking soda that was added? In other words, do these values reflect the total mass lost from baking soda and vinegar, or just the mass lost from vinegar?

Chris

[lil bit]

Chris, yes the weights do include the baking soda.

[deleted-71447]

OK, thanks. I have nothing to add then.