# Why does vinegar and baking soda yield a far smaller volume of carbon dioxide gas than expected from calculation?

I experimented $$\ce{CO2}$$ generation by adding $$\pu{4 g}$$ of $$25\%$$ acetic acid water solution ($$= \pu{1 g}$$ of acetic acid) to $$\pu{1.4 g}$$ of pure baking soda. But this mixture yielded only $$50\%$$ less than the calculated amount $$\pu{373 mL}$$ of $$\ce{CO2}$$.

$$M(\ce{CH3COOH}) = \pu{60g/mol}, M(\ce{NaHCO3}) = \pu{84 g/mol}\\ \implies \ce{CH3COOH}~\pu{1g} : \ce{NaHCO3} \pu{1.4 g}. \\ \ce{CH3COOH + NaHCO3 -> CH3COONa + H2O + CO2}\\ \text{mol to mol} = \pu{1 mol} ~\ce{CO2}, M(\ce{CO2}) = \pu{44 g/mol} \\ \implies \ce{CO2}~\pu{0.733g} : \ce{CH3COOH}~\pu{1g} : \ce{NaHCO3}~\pu{1.4g}\\ \text{Gas} = \pu{22.4 L/mol} \implies \pu{22.4 L}/60 = \pu{373.3 mL} (= \pu{0.733 g}) \text{(Theoretical yield)}.\\ \text{Actual yield} = \pu{190 mL} \text{by volume measurement} (50\%)\\ \text{Actual yield} = \pu{0.586 g} (=\pu{298.6 mL}) \text{by mass measurement} (80\%)\\$$

I set the water filled measuring cup upside down above the water filled plate, and attached hose underneath the skirt of the cup so that any gas generated from the sealed bottle of the mixture to get provided into the measuring cup.

Moreover, I checked the amount of $$\ce{CO2}$$ yielded by the weight loss method. That is, I measured the mixture above the scale to see how much $$\ce{CO2}$$ is evaporated during the chemical reaction.

The above 2nd method provided me with $$80\%$$ yield.

$$50\%$$ of air volume and $$80\%$$ of mass are coming with the consistency during the several times of experiments.

What was wrong with my experiment??

• Watch this guy. youtube.com/watch?v=5pPPFI8E33U . He also has consistant 45% percent yields. Commented Sep 11, 2018 at 8:50
• The rest of CO2 is still dissolved in water. CO2 is partly soluble in water. Commented Mar 7, 2020 at 19:40
• I have updated (at least I tried) your post with chemistry markup. If you want to know more, please have a look here and here. It would have been easier if you were not using some text equations, please check if I have destroyed anything in the process. Commented Mar 8, 2020 at 0:19

I'm assuming your calculations and materials are correct here. Acetic acid is a weak acid and as such will for a buffer solution with a weak base. So at half your reaction completion you will have generated a sodium acetate buffer with pH ~5. At this stage the acidity of your solution might not be enough to protonate all the carbonate.

Try to add a stronger acid if you can.

• Oh, I missed one thing. I already tried 4g of acetic acid + 1.4g of sodium bicarbonate only to have just around 50% yield. In this case, acidity is already high enough and still keeps high even after reacting with 1.4g of sodium bicarbonate, but why the yield doesn't get higher?? Commented Sep 11, 2018 at 7:44
• How did you test for acidity? What pH did you have? Commented Sep 11, 2018 at 7:53
• I didn't. I added 100% acetic acid solution bought from lab material shopping mall to the tap water. Tests were done in order of #1 1 g acetic acid without water, #2 1g acetic + 3g water, #3 2g acetic + 3g water, #4 3g acetic + 3g water, #5 4g acetic + 3g water, #6 2g acetic without water, #7 3g acetic without water, with fixed amount of Arm & Hammer backing soda which is 1.4g. Commented Sep 11, 2018 at 8:10
• You can try different amounts of baking soda to make sure it is actually pure bicarbonate. Commented Sep 11, 2018 at 8:19
• Watch this guy. youtube.com/watch?v=5pPPFI8E33U . He also has consistant 45% percent yields. Commented Sep 11, 2018 at 8:49

First, use freshly bought $$\ce{NaHCO3}$$ as on warming, it converts into more alkaline $$\ce{Na2CO3}$$.

$$\ce{2 NaHCO3 -> Na2CO3 + H2O (g) + CO2 (g)}$$

See this article: 'Vanishing Baking Soda' at the Scientific American.

Next, my experience with generating $$\ce{CO2}$$ is that you can collect it over water, but depending on the level agitation/bubbling, you likely suffer a loss due to the dissolution of the $$\ce{CO2}$$! In fact, you can use this to crush a plastic vessel fill with $$\ce{CO2}$$ and a little water which is tightly sealed. Upon shaking, the $$\ce{CO2}$$ rapidly goes into solution causing an implosion.

Bottom line, bubbling $$\ce{CO2}$$ through water may result in seemingly reduced yield from carbon dioxide dissolving.

To test, replace the tap water with freshly boiled (and still hot) $$\ce{NaCl}$$ rich water, and report results.