Which ions actually form the precipitate?
You will be able to: Translate a formula equation into complete and net ionic equations.
Which ions actually form the precipitate?
Two clear salt solutions can make a cloudy solid. Many dissolved ions are still swimming in the water afterward. A net ionic equation focuses on the species that underwent the represented change.
A useful starting point: How do coefficients conserve atoms? →
Words and symbols before equations
- Aqueous, (aq)
- Dissolved in water; the label does not itself mean completely ionized.
- Strong electrolyte
- A substance represented as separated ions in aqueous solution.
- Spectator ion
- An ion unchanged on both sides of the complete ionic equation.
- Precipitate
- A solid formed from a solution.
What this picture assumes
AgCl is stated to precipitate. Soluble strong electrolytes are dissociated; the solid remains intact. Equilibrium dissolved amounts are omitted.
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.
- AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq). Aqueous salts: soluble strong electrolytes. AgCl(s): supplied precipitate
- Check what the picture assumes below. Use the Explore task to predict one change before moving a control.
Connect the picture to the chemistry
For the stated reaction AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq), the soluble salts are strong electrolytes. AgCl is given to be sparingly soluble.
Separate the aqueous strong electrolytes into ions, keeping their coefficients and charges: Ag⁺ + NO₃⁻ + Na⁺ + Cl⁻ → AgCl(s) + Na⁺ + NO₃⁻.
Cancel only identical species with the same state and charge on both sides. Na⁺ and NO₃⁻ are spectators. Ag⁺(aq) + Cl⁻(aq) → AgCl(s) conserves Ag, Cl and net charge zero.
Keep solids, liquids, gases and weak electrolytes intact in this representation. An aqueous weak acid is not automatically split just because it is labeled (aq).
A worked example, step by step
Write the net ionic equation for the stated reaction BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq). BaSO₄ is given to precipitate.
- Write Ba²⁺ + 2Cl⁻ + 2Na⁺ + SO₄²⁻ → BaSO₄(s) + 2Na⁺ + 2Cl⁻.
- Identify unchanged 2Na⁺ and 2Cl⁻ on both sides.
- Cancel those spectators: Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s).
- Check one Ba, one S, four O and charge zero on both sides. The solid stays intact.
Do not split an insoluble solid into aqueous ions; that would erase the precipitate you are representing.
Are spectator ions removed from the beaker?
Compare with an explanation
No. They are omitted from the net equation because they remain unchanged.
Predict. Change one thing. Explain.
Switch from the formula equation to the complete ionic equation and then the net ionic equation. Identify which species disappear from the written equation but remain physically in solution.
On narrow screens, swipe or scroll diagrams sideways to read all labels.
AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq). Aqueous salts: soluble strong electrolytes. AgCl(s): supplied precipitate
AgCl is stated to precipitate. Soluble strong electrolytes are dissociated; the solid remains intact. Equilibrium dissolved amounts are omitted.
Explain what you noticed: Answer the investigation prompt above. State one observation and explain it using conserved atoms/charge, reaction ratios, particle identity or electron/proton transfer. 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 questionGiven Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq), with PbI₂ stated to precipitate, write the complete ionic and net ionic equations and check charge.
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Compare with the answer and four-point rubric
- 1 point: Pb²⁺ + 2NO₃⁻ + 2K⁺ + 2I⁻ → PbI₂(s) + 2K⁺ + 2NO₃⁻.
- 1 point: Identify K⁺ and NO₃⁻ as spectators.
- 1 point: Pb²⁺(aq) + 2I⁻(aq) → PbI₂(s).
- 1 point: Charge is +2 − 2 = 0 on the left and zero on the right; atom counts also match.
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 1What is a spectator ion?
An ion unchanged in the complete ionic equation.
RECALL 2What does a net ionic equation retain?
Species undergoing the represented chemical change.
RECALL 3Must every aqueous substance be split?
No; weak electrolytes remain intact in this representation.
Revisit these tomorrow and a week later. Try a fresh problem and explain why the method applies.
Which ions actually form the precipitate?
- Formula equation → aqueous strong-electrolyte ions → cancel identical spectators.
- Atom counts and total charge must agree.
Remember: Do not split an insoluble solid into aqueous ions; that would erase the precipitate you are representing.
Conditions: AgCl is stated to precipitate. Soluble strong electrolytes are dissociated; the solid remains intact. Equilibrium dissolved amounts are omitted.
Refresh Kid · AP Chemistry Unit 4 · Objectives 4.2.A · Review edition
Framework, scope and review status
Mapped to College Board CED, Topic 4.2, objective 4.2.A. CED effective Fall 2024 and June 2026 clarifications checked September 16, 2026. Unit 4: Chemical Reactions, Topics 4.1–4.9. 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. Solubility facts for sodium, potassium, ammonium and nitrate salts are included; other precipitation cases give the needed information. Lewis acid-base theory and the labels oxidizing/reducing agent are not treated as required exam content. Quantitative pH, equilibrium and electrochemical potentials are developed in later units. Stoichiometric models state complete-reaction assumptions; they are not mechanisms or equilibrium simulations.
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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