SCIENCE · INVESTIGATE AND EXPLAIN

Connect a measured mass to a particle amount

Compare two samples using mass, moles and explicitly named entities.

Learning outcome: Convert mass to amount using molar mass and distinguish equal masses from equal molecule numbers.

Starting recap

Scientific notation 6.02 × 10^23 means 6.02 multiplied by a power of ten. A ratio can convert units.

All lessons are open directly. Your saved experiments remain when you leave and return.

Try

18 g water and 44 g carbon dioxide have different masses. Could they contain the same number of molecules?

Open the experiment

Predict

Predict which sample has more molecules when each mass is 44 g. Explain what information you need besides mass.

Your prediction and reason

Experiment

Capture (18,44), then (44,44), then (9,22). Compare equal amounts, equal masses and half-sized samples. Keep the entity labels.

Compare mass, amount and molecule number

Worked teaching model · synthetic values · Separate pure samples; rounded teaching molar masses H2O = 18 g/mol and CO2 = 44 g/mol. These are not exact physical constants. Avogadro constant is exact; computed counts inherit mass and molar-mass assumptions.

Water sample mass: 18 g Carbon dioxide sample mass: 44 g

Reset keeps your prediction, captures and practice history.

Read left to right: each conversion uses the quantity and units from the preceding box. NA denotes the Avogadro constant; notation such as 6.022e+23 means 6.022 × 10^23 molecules.

Calculated values on the same fixed scale
Row	Quantity	Value (mol)
1	Water amount (H2O molecules)	1
2	Carbon dioxide amount (CO2 molecules)	1

1.0000 mol H2O; 1.0000 mol CO2.

Amount n = mass m / molar mass M. Water molecules ≈ 6.0221e+23; CO2 molecules ≈ 6.0221e+23. Entity counts refer to molecules, not total atoms. Display rounding is not additional measurement precision.

Observation to attach to a capture

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

Specify what you are counting

A dozen means twelve specified objects; a mole is an amount containing a much larger specified number of entities. One mole contains exactly 6.02214076 × 10^23 entities. The entity could be an atom, molecule, ion or another specified particle or group. Always say which. The Avogadro constant NA is 6.02214076 × 10^23 per mole. SI definition of the mole, BIPM.

One mole of water molecules contains two moles of hydrogen atoms and one mole of oxygen atoms. It does not contain just one mole of atoms in total. One mole of carbon dioxide molecules likewise contains three moles of atoms, but in a different elemental composition. Counting all atoms together loses information needed to distinguish the substances.

Use mass as a bridge

Particles of different substances have different masses. Molar mass M is mass per mole, expressed here in grams per mole (g/mol). This teaching lab uses rounded values: water 18 g/mol and carbon dioxide 44 g/mol. These are approximations chosen for arithmetic, not exact constants or a claim about every isotope composition.

Let m be sample mass in grams and n be amount in moles. Then n = m/M. Read it as: divide mass by mass per mole to obtain moles. The units cancel as g/(g/mol) = mol. To recover mass, multiply: m = nM.

For 18 g water, n = 18/18 = 1 mol. For 44 g CO2, n = 44/44 = 1 mol. The masses differ, but the molecule amounts match. At equal masses of 44 g, water has 44/18 ≈ 2.444 mol while CO2 has 1 mol. An equal mass comparison is not an equal molecule-number comparison.

Convert the amount to entities

Entity number N = n × NA. For 9 g water, n = 0.5 mol and N = 0.5 × 6.02214076 × 10^23 ≈ 3.011 × 10^23 water molecules. This sample has twice as many H atoms as water molecules. Scientific notation keeps a very large number readable; it does not imply unusual units.

The defining constant is exact, but a calculated particle count still inherits uncertainty from sample mass, purity and molar mass. An instrument reading rounded to a gram does not suddenly become exact when multiplied by an exact constant. The app displays approximate counts; those decimal places are not a certificate of measurement precision.

Predict, then check: compare 36 g water with 88 g CO2. Then halve only the water sample. Which ratio changes, and which property of each substance stays fixed?

Check the sample comparison

Initially both samples contain 2 mol of molecules. Halving the water mass makes its amount 1 mol while CO2 remains 2 mol. Their molar masses remain 18 and 44 g/mol in this model. Sample size changes, substance-specific conversion factors do not.

Apply the conversion beyond the chosen samples

A pure substance has molar mass 50 g/mol. A 12.5 g sample contains 12.5/50 = 0.25 mol of the specified entities. If those entities are formula units of a salt, call them formula units rather than molecules. A mixture needs composition information before its total mass can be converted into the amount of any one constituent.

In your reflection, show one unit-canceling calculation, identify the entities and state which quantities were measured, assumed or defined. The two samples in this lab are compared separately; the controls do not combine them or model a reaction.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

Use unit cancellation to explain the comparison. Distinguish one mole of water molecules from one mole of hydrogen atoms.

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Choose a conductor using two explicit constraints Next: Predict product mass without rounding away reactants

Save a science backup or import one

Science work is stored locally in this browser, separately from mathematics and AI. It does not sync automatically. Use this science-only backup; this checkout's older all-subject export does not include science.

A legacy file is available only when the complete snapshot fits the 36 MB limit. For larger snapshots, prepare a complete file set below; never discard notebooks to make a smaller file.

Choose a science backup (maximum 36 MB)

Matching imported notebook drafts replace their current drafts. Omitted lessons and known first attempts remain. Export your current work first if you want to retain both drafts.

Complete file sets and course backups

A file set can hold more work than one science file. Keep its manifest and every part together. Each file is limited to 36 MB. This format needs this version of LearnAI or a compatible newer version; older versions can use only the legacy single-file backup above.

Export scope

The set includes every saved science course and global continuation at this moment. Later edits need a new export. A conflicting tab exports its own visible work, which may differ from saved work in another tab.

Choose the manifest and all parts together

0 file(s) selected. File order and filenames do not determine identity. Missing, changed or conflicting parts block the entire restore; no good part is applied by itself.

Science storage: loading. No account or remote computation is required.