SCIENCE · INVESTIGATE AND EXPLAIN

Check phase existence before imposing saturation

Leaving a pure solid out of a quotient does not supply unlimited material.

Learning outcome: Cross the n=.20V boundary. Record dissolved inventory, surviving solid and aqueous activity; distinguish undersaturated, saturated-with-solid and exact-boundary states.

Starting recap

Refresh dimensionless activities, component balances, admissible roots, normalized partial pressures and independent versus shared measurement errors.

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Try

With saturation concentration .20 M, .30 mol added to 1 L leaves .20 mol dissolved and .10 mol solid. In 2 L, all .30 mol dissolves and concentration is .15 M.

Open the experiment

Predict

Can the same amount produce a saturated mixture in one volume but an undersaturated solution in another?

Your prediction and reason

Experiment

Cross the n=.20V boundary. Record dissolved inventory, surviving solid and aqueous activity; distinguish undersaturated, saturated-with-solid and exact-boundary states.

Check whether a pure solid phase survives

Worked teaching model · synthetic values · Fictional pure S(s)⇌S(aq), ideal solute activity c/c°, c°=1 M, saturation K=.20 at fixed temperature. Negligible dissolution volume change. A pure solid has unit activity only while that phase exists; no ionic Ksp or particle dissociation here.

Total added S: 0.3 mol Solvent solution volume: 1 L

Reset keeps your prediction, captures and practice history.

Equilibrium dissolved concentration: solid
Remaining solid concentration-equivalent: long dashes

Axes rescale. A quotient comparison, inventory intersection and relaxation trajectory have different horizontal meanings; inspect labels rather than treating every curve as elapsed time.

All calculated plot coordinates

Equilibrium dissolved concentration
total added amount (mol)	concentration or amount/volume (mol/L)
0	0
0.01	0.01
0.02	0.02
0.03	0.03
0.04	0.04
0.05	0.05
0.06	0.06
0.07	0.07
0.08	0.08
0.09	0.09
0.1	0.1
0.11	0.11
0.12	0.12
0.13	0.13
0.14	0.14
0.15	0.15
0.16	0.16
0.17	0.17
0.18	0.18
0.19	0.19
0.2	0.2
0.21	0.2
0.22	0.2
0.23	0.2
0.24	0.2
0.25	0.2
0.26	0.2
0.27	0.2
0.28	0.2
0.29	0.2
0.3	0.2
0.31	0.2
0.32	0.2
0.33	0.2
0.34	0.2
0.35	0.2
0.36	0.2
0.37	0.2
0.38	0.2
0.39	0.2
0.4	0.2
0.41	0.2
0.42	0.2
0.43	0.2
0.44	0.2
0.45	0.2
0.46	0.2
0.47	0.2
0.48	0.2
0.49	0.2
0.5	0.2
0.51	0.2
0.52	0.2
0.53	0.2
0.54	0.2
0.55	0.2
0.56	0.2
0.57	0.2
0.58	0.2
0.59	0.2
0.6	0.2

Remaining solid concentration-equivalent
total added amount (mol)	concentration or amount/volume (mol/L)
0	0
0.01	0
0.02	0
0.03	0
0.04	0
0.05	0
0.06	0
0.07	0
0.08	0
0.09	0
0.1	0
0.11	0
0.12	0
0.13	0
0.14	0
0.15	0
0.16	0
0.17	0
0.18	0
0.19	0
0.2	0
0.21	0.01
0.22	0.02
0.23	0.03
0.24	0.04
0.25	0.05
0.26	0.06
0.27	0.07
0.28	0.08
0.29	0.09
0.3	0.1
0.31	0.11
0.32	0.12
0.33	0.13
0.34	0.14
0.35	0.15
0.36	0.16
0.37	0.17
0.38	0.18
0.39	0.19
0.4	0.2
0.41	0.21
0.42	0.22
0.43	0.23
0.44	0.24
0.45	0.25
0.46	0.26
0.47	0.27
0.48	0.28
0.49	0.29
0.5	0.3
0.51	0.31
0.52	0.32
0.53	0.33
0.54	0.34
0.55	0.35
0.56	0.36
0.57	0.37
0.58	0.38
0.59	0.39
0.6	0.4

Calculated under the declared model
Quantity	Value	Unit
Dissolved amount	0.2	mol
Remaining pure solid	0.1	mol
Dissolved concentration	0.2	mol/L
Aqueous activity	0.2	dimensionless

A pure solid remains and the solution is saturated.

Omitting a pure solid from a quotient does not mean unlimited solid exists. At the equality boundary the solution is saturated but bulk solid amount is zero; below it, imposing c=.20 M would create matter. This is a finite inventory illustration, not a nucleation or dissolution-rate prediction.

These calculated packets are not performed chemical measurements. Keep feasible inventories, activity conventions, fitting observations and independent checks distinct.

A pure solid remains and the solution is saturated.

Observation to attach to a capture

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

Understand

Ask whether the phase exists

For the fictional dissolution S(s)⇌S(aq), the pure solid activity is one when that pure phase exists. With ideal dissolved activity c/c° and K=.20 at the declared temperature, a coexisting solid fixes the saturation concentration at .20 M for c°=1 M.

This relation does not guarantee a solid survives. At fixed solution volume V and added amount n, dissolved amount is the smaller of n and .20V. Remaining solid is their difference. The model neglects dissolution-induced volume change and does not claim any real substance has these parameters.

Compare the same inventory in two volumes

At n=.30 mol and V=1 L, .20 mol dissolves and .10 mol remains. At V=2 L, saturation would require .40 mol, more than was added. All .30 mol dissolves, giving .15 M and no bulk solid. Enforcing .20 M in this second state would create matter.

Treat the boundary precisely

When n=.20V exactly, the solution reaches saturation with zero remaining bulk solid. Do not round this into a positive solid inventory. The equality case is distinct from a finite coexisting phase and from an undersaturated solution. These equilibrium constraints do not predict induction time, supersaturation persistence or nucleation kinetics.

Transfer and check

For .40 mol added to 1.50 L, predict .30 mol dissolved, .10 mol solid and .20 M solution. Then remove the solid without changing the liquid volume or concentration in the ideal accounting: the liquid remains saturated at that instant, but no reservoir of solid remains to buffer subsequent dilution. Explain why phase presence is part of the evidence, not an optional label.

Source and evidence boundary

Conceptual reference checked 30 October 2026: OpenStax Chemistry 2e. These original hypothetical packets use explicitly defined activities, inventories and response assumptions. No material is mixed, heated, pressurized or measured. Numerical compatibility does not certify practical technique or uniquely establish a real chemical mechanism. Retain your prediction, feasible inventory, quotient check and changed-case interpretation.

Apply

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

Why would imposing saturation below the supply threshold violate material conservation?

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.

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