Will a precipitate form when two solutions are mixed?
You will be able to: Apply dilution before comparing the ion product with Ksp.
Will a precipitate form when two solutions are mixed?
Mixing two clear salt solutions can produce a cloudy solid. The decisive comparison uses the ion concentrations after mixing, not the concentrations printed on the original bottles.
A useful starting point: Can you rank solubility by comparing Ksp numbers alone? →
Words and symbols before equations
- Ion product Qsp
- Current product of dissolved ion concentrations for the dissolution equation.
- Precipitation threshold
- Saturation boundary where Qsp=Ksp.
- Supersaturation
- Qsp exceeds Ksp; solid formation is thermodynamically favored.
- Total volume
- Combined solution volume under the additive-volume approximation.
What this picture assumes
Ideal dilute concentrations in mol/L (M); fixed temperature, fixed volume except when explicitly changed, and no side reactions. Supplied K values use the stated AP concentration convention. Mix 50.0 mL of M⁺ stock at 2×10⁻⁴ M with 50.0 mL X⁻ stock. Additive volume, MX Ksp=10⁻⁸. Immediate ion product predicts precipitation tendency, not nucleation speed or final precipitate mass.
Read the picture in three steps
- Read the species and labels first. Identify what each symbol and line represents. Read the units and fixed conditions before comparing quantities.
- Qsp>Ksp: net precipitation is favored; nucleation or slow kinetics may delay visible solid.
- Check what the picture assumes below. Use the Explore task to predict one change before moving a control.
Connect the picture to the chemistry
First calculate moles of each relevant ion from its stock concentration and volume. Divide by the combined volume to obtain immediate mixed concentrations before precipitation.
For a one-to-one salt, Qsp=[M⁺][X⁻]. If Qsp>Ksp, net precipitation is favored; if Qsp<Ksp, the solution is unsaturated with respect to this solid.
At Qsp=Ksp the mixture is at the saturation threshold. A visible cloud may require time and nucleation; Q/K predicts tendency rather than observable speed.
Ignore spectator-ion effects, complex formation and nonideal activity corrections in this introductory dilute model. A Qsp>Ksp result does not imply every ion is removed.
A worked example, step by step
Mix 50.0 mL of 2.0×10⁻⁴ M M⁺ with 50.0 mL of 4.0×10⁻⁴ M X⁻. For MX, Ksp=1.0×10⁻⁸. Predict precipitation.
- Total volume is 100.0 mL.
- Each stock is diluted by two: [M⁺]=1.0×10⁻⁴ M and [X⁻]=2.0×10⁻⁴ M.
- Qsp=2.0×10⁻⁸.
- Qsp>Ksp, so net precipitation is favored; final dissolved concentrations will still satisfy the equilibrium relation if solid remains.
Comparing undiluted stock concentrations with Ksp can give a wrong precipitation prediction.
Does Qsp>Ksp mean precipitation happens instantaneously?
Compare with an explanation
No. It predicts the favored net change; nucleation and kinetics can delay visible solid.
Predict. Change one thing. Explain.
Keep equal 50 mL volumes and the M⁺ stock fixed. Change the X⁻ stock, calculate diluted values and locate the saturation boundary.
On narrow screens, swipe or scroll diagrams sideways to read all labels.
Qsp>Ksp: net precipitation is favored; nucleation or slow kinetics may delay visible solid.
Ideal dilute concentrations in mol/L (M); fixed temperature, fixed volume except when explicitly changed, and no side reactions. Supplied K values use the stated AP concentration convention. Mix 50.0 mL of M⁺ stock at 2×10⁻⁴ M with 50.0 mL X⁻ stock. Additive volume, MX Ksp=10⁻⁸. Immediate ion product predicts precipitation tendency, not nucleation speed or final precipitate mass.
Explain what you noticed: Answer the investigation prompt above. State one observation and explain it using relative rates, particle conservation, the Q/K comparison or the stated dissolution equilibrium. Identify what the representation cannot tell you.
Apply the idea to a fresh problem Practice →Show what you understand.
Two original questions are a starting check, not proof of mastery. Explain your choice before revealing the answer.
Original written challenge
4 points · self-check · not an official AP questionMix equal volumes of 4×10⁻⁴ M M⁺ and 2×10⁻⁴ M X⁻. MX has Ksp=3×10⁻⁸. Find immediate concentrations, Qsp and the expected tendency.
This response is not submitted or saved. Copy it before leaving.
Compare with the answer and four-point rubric
- 1 point: [M⁺]=2×10⁻⁴ M after mixing.
- 1 point: [X⁻]=1×10⁻⁴ M after mixing.
- 1 point: Qsp=2×10⁻⁸.
- 1 point: Qsp<Ksp, so the mixed solution is unsaturated and precipitation is not favored for MX.
Accept equivalent correct methods and explanations. This is a Refresh Kid teaching rubric, not an official AP scoring guideline.
Retrieve it before you reveal it.
RECALL 1Why dilute first?
The ions occupy the combined volume.
RECALL 2What does Qsp=Ksp mean?
The saturation threshold/equilibrium relation.
RECALL 3Are all ions removed when solid forms?
No; dissolved ions remain at equilibrium.
Revisit these tomorrow and a week later. Try a fresh problem and explain why the method applies.
Will a precipitate form when two solutions are mixed?
- After mixing: [ion]=moles of ion/total volume.
- Qsp>Ksp favors precipitation; Qsp<Ksp is unsaturated.
Remember: Comparing undiluted stock concentrations with Ksp can give a wrong precipitation prediction.
Conditions: Ideal dilute concentrations in mol/L (M); fixed temperature, fixed volume except when explicitly changed, and no side reactions. Supplied K values use the stated AP concentration convention. Mix 50.0 mL of M⁺ stock at 2×10⁻⁴ M with 50.0 mL X⁻ stock. Additive volume, MX Ksp=10⁻⁸. Immediate ion product predicts precipitation tendency, not nucleation speed or final precipitate mass.
Refresh Kid · AP Chemistry Unit 7 · Objectives 7.11.A · Review edition
Framework, scope and review status
Mapped to College Board CED, Topic 7.11, objective 7.11.A. CED effective Fall 2024 and June 2026 clarifications checked September 17, 2026. Unit 7: Equilibrium, Topics 7.1–7.12. Focused lesson names, examples, models and assessments are original Refresh Kid teaching materials, not additional official topics or official AP questions. Official corrections.
The model states its assumptions beside the diagram. Converting between Kc and Kp and calculations for a dissolved species in equilibrium with its gas phase are excluded from assessed Unit 7 scope. Concentrations use mol/L and gas partial pressures use the stated pressure convention. Supplied constants are teaching data at fixed temperature unless otherwise specified. Ideal dilute-solution and ideal-gas approximations are stated. 3D views show inventories, not molecular trajectories, measured structures or proof of equilibrium from a single snapshot. Approximation checks are explicit; a small K alone does not justify neglecting every change.
Teaching resources: The Organic Chemistry Tutor video titles/descriptions and topic coverage were checked for optional links; no claim is made to have watched every video. No creator scripts, examples, worksheets or artwork were copied. GitHub’s 3D website collection and its Three.js camera-control example informed the idea of controllable spatial inspection. Scientific diagrams, geometry and interactions here are original. The self-hosted Three.js runtime retains its MIT license. Camera rotation changes the view, not the chemistry.
Independent teacher review and observation of students remain pending. Implementation checks do not certify scientific accuracy, accessibility or learning effectiveness. This is a review edition.
Optional official resource: Released AP Chemistry questions and scoring guides. This archive contains questions across units; it is not an assignment of every question to this lesson.
The teaching sequence is informed by the IES learning guide; this exact implementation has not been evaluated with learners.
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