The balance is empty and reads 0.0 g.

About this model

Time is sped up. The real reaction fizzes for about a minute; here it takes a few seconds.
These readings are typical values for this investigation, rounded to a tenth of a gram.
In a real open bottle a little carbon dioxide stays dissolved in the liquid, so a measured loss is slightly smaller than the calculated 2.1 g.
The cap sits on the balance from the start. If it waited on the bench, screwing it on would add its own mass to the reading at the exact moment this lab says nothing changed. On the pan it can only move mass around inside the system.
The dotted line is an ionic bond. Baking soda and sodium acetate are not really molecules. Each is a positive sodium ion held to a negative ion by the attraction between their opposite charges. That IS a bond, but it is not a shared pair of electrons, so it is not drawn as a solid stick. The + and − show where the charges sit. In real baking soda the ions repeat in a lattice rather than pairing off; they are drawn in pairs here so the atoms in the formula can be counted, which is what this standard asks for.
The bottle is rigid. A sealed bag would puff up and push against the air, and the balance would read a small loss even though nothing left.
You cap it before the reaction starts. In a real lab you would tip the baking soda in and close the bottle in one motion, and a little gas still gets out while you do. Here the powder waits until you choose, so both runs land on a clean number.

Run the investigation Click the bottle of vinegar to stand it on the balance.

You can click the bottle, the scoop and the cap on the bench itself, or use these buttons.

Step 1 of 4

Where did the mass go?

Runs completed: 0 of 2

Both results stay here, so you can compare them without writing anything down.

Baking soda and vinegar react and make a gas. Stand the bottle on the balance, measure out the baking soda, pour it in, and watch the reading. Do it twice: once with the bottle open so the gas can get out, and once with the cap on so it cannot.

Try this

The procedure calls for 4.0 g of baking soda. Each scoop holds 1.0 g, so take four of them. Watch the balance the whole time: it reads the bottle, the cap and everything in the bottle, and it never lies about what is still there.

Run it open and closed first.

Same atoms on both sides. They are only rearranged.

About this model

Atoms have no color. These colors are a standard code chemists use so you can tell the elements apart.
Not to scale, and not flat. Real atoms are far smaller than these circles and a real molecule is three dimensional.
The shapes are simplified. The number of each kind of atom is exact. The arrangement drawn here is a model, not the real shape of the molecule.
Only the atoms in the equation are drawn. The water in the vinegar and the bottle itself are not shown.
The dotted line is an ionic bond. Baking soda and sodium acetate are not really molecules. Each is a positive sodium ion held to a negative ion by the attraction between their opposite charges. That IS a bond, but it is not a shared pair of electrons, so it is not drawn as a solid stick. The + and − show where the charges sit. In real baking soda the ions repeat in a lattice rather than pairing off; they are drawn in pairs here so the atoms in the formula can be counted, which is what this standard asks for.

What photosynthesis builds, over thirty years

This oak weighs about 900 kg. Almost all of that was built by the reaction you just modelled: carbon dioxide from the air and water from the soil. About half a tree’s dry mass is carbon, and every carbon atom arrived as a gas. Source: USDA Forest Service.

Pick a reaction Start with hydrogen peroxide.

Step 2 of 4

Follow every atom

Reactions modeled: 0 of 3

A chemical reaction takes the atoms in the reactants apart and builds them into new products. The arrow is the reaction itself: it means becomes. It is not an equals sign and it is not a direction of travel. Nothing is added and nothing is thrown away across it, so every atom on the left has to turn up again on the right. Model all three reactions and watch the tally under each side.

Atom	Reactants	Products

Try this

Before you press Rearrange, count the red oxygen atoms on the left. Now count them on the right after. In a chemical formula, the small subscript tells you how many atoms of that element are in one molecule or formula unit. The big number in front is the coefficient, and it tells you how many of that whole molecule take part.

Model all three reactions first.

Both sides of a chemical equation have to weigh the same, because the atoms are only rearranged. One mass here was never measured.

Total each side. The side with the blank has to reach the same number as the other one.

About this model

These masses are real. Each one is worked out from the amount stated, rounded to a tenth of a gram. In the first reaction the carbon dioxide comes to 2.1 g, which is exactly what your balance lost on the open run in step 1.
The equations are already balanced. Balancing one yourself is high school chemistry. Your job here is to read the masses off a balanced equation and use the fact that both sides must total the same.

Pick a reaction Start with the baking soda reaction you ran in step 1.

Step 3 of 4

Find the missing mass

Solved: 0 of 3

Nothing is created and nothing is destroyed, so the reactants and the products have to weigh the same. Add up the side you can, compare it with the other side, and work out the mass that is missing.

How to do it

Solve all three first.

Conservation Lab

Step 1 of 4

Where did the mass go?

Step 2 of 4

Follow every atom

Step 3 of 4

Find the missing mass

Step 4 of 4

Challenge