Why is the mass loss only about 5 g when you said 4.1 litres of gas?

Because carbon dioxide is heavy. At room temperature one mole weighs 44 g, and 0.167 mol is 7.3 g. Some of that gas stays dissolved in the liquid as bicarbonate and some escapes slowly after the foam collapses, so the measured loss sits a little under the theoretical value.

Does more foam mean more gas?

No. Foam height depends on bubble size, which depends on the jug's width and the trace proteins in the vinegar. A narrow cylinder always shows a taller foam for the same reaction.

Can I do this in a sealed bottle to capture the gas?

You can, with a balloon over the neck, but a sealed rigid bottle will build pressure fast. Use a bottle rated for carbonated drinks, never glass, and keep the balloon small so it cannot pop back into the liquid.

Measuring the Foam: How Much Gas Baking Soda Really Makes

Everyone has seen the volcano. Almost nobody has measured it. With a kitchen scale and a tall jug you can weigh the carbon dioxide that escapes and compare it with the 1:1 reaction the textbook predicts.

Difficulty 2/5 · Steady hands 25 min Grade 1 · everyday Bench date 2 Sep 2026 By The Lab Bench

Isometric glassware cross-section: liquid level matches difficulty 2 and the bubble column matches a 25 minute run

Materials

Substitutes are listed for anything you may not have; amounts are for one run as written.
Item	Amount	If you do not have it
Baking soda (sodium bicarbonate)	20.0 g, weighed	Bicarbonate of soda, same substance
White vinegar, 5% acetic acid	200 ml	Distilled white vinegar; do not use malt vinegar
Tall narrow jug	1, at least 1 litre	A measuring cylinder gives a better foam height reading
Kitchen scale	1, accurate to 0.1 g	0.5 g accuracy is enough for the mass reading
Ruler	1	A tape measure held against the jug
Tray or rimmed baking sheet	1	A large plate; the foam always overshoots

Method

Stand the jug on the tray, pour in 200 ml of vinegar, and weigh the whole assembly. Write the number down.

Watch for: The vinegar plus jug plus tray should read about 700 g depending on your glassware.

Weigh 20.0 g of baking soda into a small cup.

Watch for: 20 g of baking soda is about four level teaspoons, or 14 ml by volume.

Tip the baking soda in all at once and start the timer. Do not stir.

Watch for: Foam reaches the lip of a one-litre jug in 6 to 9 seconds and then climbs down the outside.

Measure the maximum foam height with the ruler, then wait for the foam to collapse completely.

Watch for: Peak height depends heavily on how narrow the jug is, not on how much gas was made.

Weigh the whole assembly again once the foam has fully collapsed and the liquid is still.

Watch for: The mass drops by roughly 5 g, matching the carbon dioxide that left the jug.

Why it works

Sodium bicarbonate and acetic acid react one to one: NaHCO3 plus CH3COOH gives sodium acetate, water and carbon dioxide. Twenty grams of baking soda is 0.238 mol, and 200 ml of five percent vinegar contains about 0.167 mol of acetic acid, so the vinegar is the limiting reagent. The reaction therefore produces about 0.167 mol of carbon dioxide, which at room temperature is roughly 4.1 litres of gas. The bubbles you see are that gas being trapped by the sodium acetate solution and a little residual protein; they are not proof of the reaction, only of its speed. The mass loss on the scale is the honest measurement, because carbon dioxide leaves the jug and never comes back.

Think of it like: The foam is a receipt, not the purchase. It tells you the transaction happened quickly, but the amount you actually bought is written on the scale, which is the total gas that escaped.

Clean-up and disposal

The leftover liquid is dilute sodium acetate, which is harmless and can go down the sink with plenty of water. Rinse the tray before the residue dries, because dried sodium acetate sets into a sticky film that is much harder to remove. Do not seal the jug while it is still fizzing.

Bench notes

Weighing rather than guessing

The whole point of this card is the balance. Foam height is dramatic and almost meaningless; the mass reading is boring and quantitative.

Observed / 实测With 20 g bicarbonate and 200 ml of 5 percent vinegar, the assembly loses 4.6 to 5.6 g over eight minutes, with most of it gone in the first 90 seconds.

Why the last gram takes so long

The gas that is still dissolved in the liquid has to diffuse out through a surface that is now mostly still. Stirring after the foam collapses releases the tail end of it in about ten seconds.

Observed / 实测A single stir after the foam dies drops the scale reading by another 0.4 to 0.8 g.

Doing this without redecorating the kitchen

Variations worth running

Halve the vinegar to 100 ml and predict the mass loss before you weigh. The reaction should now be limited by the acid at about 2.0 g of gas.
Use 20 g of baking powder instead of baking soda and compare the foam height. Baking powder contains only about 30 percent bicarbonate, so the foam is much smaller.
Run the same reaction in a tall narrow measuring cylinder and in a wide bowl, and compare peak foam height with identical amounts of reagent.

Questions that come up on the bench

Why is the mass loss only about 5 g when you said 4.1 litres of gas?: Because carbon dioxide is heavy. At room temperature one mole weighs 44 g, and 0.167 mol is 7.3 g. Some of that gas stays dissolved in the liquid as bicarbonate and some escapes slowly after the foam collapses, so the measured loss sits a little under the theoretical value.
Does more foam mean more gas?: No. Foam height depends on bubble size, which depends on the jug's width and the trace proteins in the vinegar. A narrow cylinder always shows a taller foam for the same reaction.
Can I do this in a sealed bottle to capture the gas?: You can, with a balloon over the neck, but a sealed rigid bottle will build pressure fast. Use a bottle rated for carbonated drinks, never glass, and keep the balloon small so it cannot pop back into the liquid.