ChemGem

How to Write Net Ionic Equations and Predict Precipitates (Step-by-Step, with Practice)

When two solutions mix, start by asking which particles are in the water. Some ions pair up into an insoluble solid, a precipitate; others stay dissolved and unchanged. This lesson predicts the solid and writes only the change that happens.

Spot it, solve it, practice it: 4 steps, 1 worked example, 7 practice problems. Free, no account.

ChemGemUpdated Section 6.3

The route · 4 steps

  1. Identify each substance’s state.
  2. Separate aqueous strong electrolytes into ions.
  3. Cancel the spectator ions.
  4. Check atoms and total charge.
Try one now See a worked example
Spot it

How to recognize net ionic equation questions

Look for two aqueous salts mixed, words like precipitate, spectator, net ionic, conducts, or electrolyte.

Example wording, with the clue words marked:

Will AgNO3(aq) + NaCl(aq) form a precipitate?

Not sure it’s this type? Compare the neighbors:

Step-by-step

Worked example: net ionic equation

The idea

What a dissolved substance puts in the water
TypeParticles in waterConducts?Examples
Strong electrolyteBreaks apart completely into ionsYesDissolved ionic compounds: NaCl → Na+ + Cl−
Weak electrolyteMostly whole molecules, a few ionsWeaklyWeak bases such as ammonia, NH3
NonelectrolyteWhole, neutral molecules; no ionsNoSugar (C12H22O11), ethanol
Moving ions carry charge, so only solutions with ions conduct electricity.
  • Ionic compounds that dissolve break into ions, so they are strong electrolytes.
  • Most molecular compounds stay as molecules, so they are nonelectrolytes.
  • Exceptions: acids and weak bases such as NH3 are molecular but form ions in water (6.4).
Solubility rules for this course
Ion groupUsuallyExceptions
Nitrates (NO3−), Group 1 salts, common ammonium (NH4+) saltsSolubleNone
Chlorides, bromides, iodidesSolubleAg+, Pb2+, Hg22+
Sulfates (SO42−)SolubleBa2+, Sr2+, Pb2+, Hg22+; CaSO4 is sparingly soluble
Carbonates, phosphates, hydroxidesPoorly solubleGroup 1 and NH4+ salts dissolve (first row); Ba(OH)2 and Sr(OH)2 are also soluble, Ca(OH)2 slightly; check your course table for others
Use this table before predicting a solid.
Before: Ag⁺, NO₃⁻, Na⁺ and Cl⁻ are dissolved, and Ag⁺ and Cl⁻ attract. After: Ag⁺ and Cl⁻ pack into solid AgCl while Na⁺ and NO₃⁻ stay dissolved as spectators. No electrons move; every ion keeps its charge. Net ionic equation: Ag⁺(aq) + Cl⁻(aq) → AgCl(s).
Ag+ and Cl− pack into solid AgCl; Na+ and NO3− stay dissolved. The solid is a repeating ionic lattice, not one AgCl molecule. Water is omitted.
Precipitation route
  • Swap ion partners.
  • Make neutral formulas.
  • Check each new formula for a solid.
  • Balance.
Writing the complete ionic equation
Split into ions
Aqueous (aq) strong electrolytes.
Keep together
Solids, liquids, gases and weak electrolytes.
From complete ionic to net ionic
  • Spectator ions: unchanged on both sides. Cross them out.
  • What remains is the net ionic equation.
  • Check both atoms and total charge.
Groups can help you recognize ions and spectators. Na is a group 1 metal, commonly forming Na⁺; Cl commonly forms Cl⁻. In AgNO₃ + NaCl, Na⁺ stays dissolved while Ag⁺ and Cl⁻ form AgCl(s). Use solubility rules and physical states. Periodic position alone does not identify every precipitate.
Groups help you recognize ions and spectators. Periodic position alone does not identify every precipitate; use the solubility rules and states.

On the periodic table: Group 1 is the far-left column below hydrogen: lithium (Li), sodium (Na), potassium (K) and the elements under them.

On the periodic table: Barium (Ba) and strontium (Sr) are in Group 2, so they form Ba2+ and Sr2+.

On the periodic table: Sodium (Na) is in Group 1, so it forms Na+. Chlorine (Cl) is in Group 17, so it forms Cl−.

On the periodic table: Ag is silver, atomic number 47 (Group 11).

Worked example · 4 steps

AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq). Find the net ionic equation.

  1. 1
    Separate dissolved ionic compounds

    Split the aqueous strong electrolytes. Keep the precipitate AgCl together.

    Ag+ + NO3− + Na+ + Cl− → AgCl(s) + Na+ + NO3−
  2. 2
    Find the unchanged ions

    Na+ and NO3− stay dissolved and do not form the solid.

    ParticleLeft sideRight sideRole
    Ag+dissolvedin AgCl(s)reacts
    Cl−dissolvedin AgCl(s)reacts
    Na+dissolveddissolvedspectator
    NO3−dissolveddissolvedspectator
  3. 3
    Cancel the spectators

    Remove the unchanged ions to show only what reacts.

    Ag+(aq) + Cl−(aq) → AgCl(s)
  4. 4
    Check conservation

    Both atoms and total charge must balance.

    LeftRight
    Ag atoms11
    Cl atoms11
    Total charge(+1) + (−1) = 00
  5. ✓
    Answer

    Ag+(aq) + Cl−(aq) → AgCl(s). Ag+ and Cl− form the precipitate; Na+ and NO3− are spectators.

Your turn

Net ionic equation practice problems

Answer first, then check. Hints open one at a time; the answer and full solution open after you try.

Problem 1 of 7 · warm-up

Will AgNO3(aq) + NaCl(aq) form a precipitate?

Hint 1 · the clue

Swap ion partners to make two new formulas. Check each one against the solubility rules, including the exceptions.

Hint 2 · the next move

Two aqueous salts are mixed and you are asked about a solid: that signals swapping partners and checking the solubility rules.

Your path:

  1. List the dissolved ions
  2. Swap partners to make two new compounds
  3. Check each with the solubility rules
  4. An insoluble one is the precipitate
Answer

Answer: Yes, AgCl(s)

Full worked solution

What you know: AgNO3(aq) and NaCl(aq) are mixed. What you want: whether a solid forms.

  1. List the dissolved ions: Ag+, NO3−, Na+, Cl−.
  2. Swap partners to get the two new neutral formulas: NaNO3 and AgCl.
  3. Check the solubility rules. NaNO3 is a nitrate and a Group 1 salt, so it dissolves. Most chlorides dissolve, but Ag+ is an exception to that rule.
  4. So a precipitate forms: Yes, AgCl(s).

Check: Ag+ (+1) and Cl− (−1) combine 1 : 1, so AgCl is neutral.

Watch out: "Chlorides dissolve" is not the whole rule. Always check the exceptions: Ag+, Pb2+, Hg22+.

On the periodic table: Sodium (Na) is in Group 1, so it forms Na⁺. Chlorine (Cl) is in Group 17, so it forms Cl⁻.

Answer: Yes, AgCl(s)

YOUR PERIODIC-TABLE REFERENCE

11NaSodium22.99Group 1 · Period 3
47AgSilver107.87Group 11 · Period 5

Atomic number identifies proton count. The decimal mass is an average, not an isotope’s mass number. Use supplied rounded masses when a problem gives them.

Problem 2 of 7

Course solubility rules: nitrates, Group 1 salts, and common ammonium salts are soluble. Name a soluble polyatomic group in these rules.

Hint 1 · the clue

Pick a soluble group that is made of more than one atom.

Hint 2 · the next move

The question asks which polyatomic group the solubility rules call soluble: read the soluble list and pick the many-atom ion.

Your path:

  1. Read the soluble line of the rules
  2. Pick ions with more than one atom
  3. Nitrate (NO3−) fits; ammonium too
Answer

Answer: Nitrate (ammonium also counts)

Full worked solution

What you know: the course solubility rules. What you want: a polyatomic ion whose salts are soluble.

  1. Read the "soluble" line of the rules: nitrates, Group 1 salts, and common ammonium salts.
  2. Pick the ones that are polyatomic (more than one atom). Nitrate is NO3−, one N and three O atoms.
  3. Nitrate salts have no exceptions in these rules, so the answer is Nitrate. Ammonium (NH4+) is also polyatomic and soluble, so it counts too.

Why it matters: If a nitrate appears in a mixing problem, it stays dissolved. It is often a spectator ion.

Watch out: Group 1 is a column of elements, not a polyatomic ion.

Answer: Nitrate

Problem 3 of 7

Sugar, C12H22O11, dissolved in water: strong electrolyte, weak electrolyte, or nonelectrolyte?

Hint 1 · the clue

Is sugar ionic or molecular? Does it form ions?

Hint 2 · the next move

You must sort a dissolved substance by electrolyte type: decide if it is ionic or molecular and whether it makes ions.

Your path:

  1. Check the formula: all nonmetals → molecular
  2. Not an acid or base → no ions
  3. No ions → nonelectrolyte
Answer

Answer: Nonelectrolyte

Full worked solution

What you know: sugar, C12H22O11, dissolves in water. What you want: its electrolyte type.

  1. Look at the formula. It has only C, H and O, all nonmetals. So sugar is a molecular compound, not ionic.
  2. Most molecular compounds dissolve as whole, neutral molecules. Sugar is not an acid or a base, so it forms no ions.
  3. No ions means nothing carries charge. Sugar is a Nonelectrolyte.

Why it matters: A sugar solution does not conduct electricity, unlike a salt solution.

Watch out: Dissolving is not the same as forming ions. Sugar dissolves well but stays as molecules.

Answer: Nonelectrolyte

Problem 4 of 7

Which solution conducts electricity: KBr(aq) or C2H5OH(aq) (ethanol)?

Hint 1 · the clue

Which one is ionic?

Hint 2 · the next move

Asking which solution conducts electricity means asking which one makes moving ions in water: compare ionic versus molecular.

Your path:

  1. Classify each compound: ionic or molecular
  2. Ionic compounds split into ions
  3. Molecular ethanol stays as molecules
  4. The one with ions conducts
Answer

Answer: KBr(aq)

Full worked solution

What you know: two solutions, KBr(aq) and C2H5OH(aq). What you want: which one conducts.

  1. Classify each compound. KBr is a metal (K) plus a nonmetal (Br), so it is ionic. Ethanol has only C, H and O, so it is molecular.
  2. A dissolved ionic compound breaks apart: KBr → K+ + Br−. It is a strong electrolyte.
  3. Ethanol stays as neutral molecules. It is a nonelectrolyte.
  4. Moving ions carry charge, so the conductor is KBr(aq).

Why it matters: Conductivity is a quick test for whether ions are present.

Watch out: The OH in ethanol is not a hydroxide ion. It is bonded inside the molecule.

Answer: KBr(aq)

Problem 5 of 7

Mixing two aqueous salts gives PbI2(s); K+ and NO3− stay dissolved. Which net ionic equation describes precipitation?

Hint 1 · the clue

A precipitate is named.

Hint 2 · the next move

A solid forms and some ions stay dissolved, and a net ionic equation is asked: drop the spectator ions.

Your path:

  1. Write the complete ionic equation
  2. Keep the solid PbI2 together
  3. Cross out spectators K+ and NO3−
  4. Check atoms and charge balance
Answer

Answer: Pb2+ + 2I− → PbI2(s)

Full worked solution

What you know: PbI2(s) forms; K+ and NO3− stay dissolved. What you want: the net ionic equation.

  1. Write the complete ionic equation. Split the aqueous salts into ions and keep the solid together: Pb2+ + 2NO3− + 2K+ + 2I− → PbI2(s) + 2K+ + 2NO3−.
  2. Cross out the ions that are unchanged on both sides: 2K+ and 2NO3−. These are spectators.
  3. What remains is Pb2+ + 2I− → PbI2(s).

Check: Atoms: 1 Pb and 2 I on each side. Charge: (+2) + 2(−1) = 0 on the left, and the solid is 0.

Watch out: Pb2+ needs two I−. Writing Pb2+ + I− leaves the charge unbalanced.

Your route: Separate aqueous strong electrolytes → Cancel spectators

On the periodic table: Potassium (K) is in Group 1, so it forms K⁺. Iodine (I) is in Group 17, so it forms I⁻.

Answer: Pb2+ + 2I− → PbI2(s)

YOUR PERIODIC-TABLE REFERENCE

7NNitrogen14.01Group 15 · Period 2
19KPotassium39.10Group 1 · Period 4
53IIodine126.90Group 17 · Period 5

Atomic number identifies proton count. The decimal mass is an average, not an isotope’s mass number. Use supplied rounded masses when a problem gives them.

Problem 6 of 7

Ag+ + NO3− + Na+ + Cl− → AgCl(s) + Na+ + NO3−: remove spectators.

Hint 1 · the clue

Separate dissolved strong electrolytes into ions. Cancel species unchanged on both sides; preserve atom and charge balance.

Hint 2 · the next move

A complete ionic equation is given and you must remove spectators: cross out ions unchanged on both sides.

Your path:

  1. Keep the solid AgCl together
  2. Find ions same on both sides
  3. Cross them out → net ionic equation
Answer

Ag+ + Cl− → AgCl(s); Na+ and NO3− are spectators.

Full worked solution

What you know: the complete ionic equation, with AgCl(s) as the solid. What you want: the net ionic equation and the spectators.

  1. The aqueous ions are already split. AgCl stays together because it is a solid.
  2. Find ions that appear unchanged on both sides: Na+ and NO3−. Cross them out.
  3. What remains is Ag+ + Cl− → AgCl(s); Na+ and NO3− are spectators.

Check: Atoms: 1 Ag and 1 Cl on each side. Charge: (+1) + (−1) = 0 on the left, and the solid is 0.

Watch out: Do not split AgCl(s) into ions. Only dissolved strong electrolytes are split.

On the periodic table: Sodium (Na) is in Group 1, so it forms Na⁺. Chlorine (Cl) is in Group 17, so it forms Cl⁻.

Answer: Ag+ + Cl− → AgCl(s); Na+ and NO3− are spectators.

YOUR PERIODIC-TABLE REFERENCE

7NNitrogen14.01Group 15 · Period 2
11NaSodium22.99Group 1 · Period 3
17ClChlorine35.45Group 17 · Period 3
47AgSilver107.87Group 11 · Period 5

Atomic number identifies proton count. The decimal mass is an average, not an isotope’s mass number. Use supplied rounded masses when a problem gives them.

Problem 7 of 7

Classify each dissolved solute as a strong electrolyte, weak electrolyte, or nonelectrolyte: CaCl2(aq), NH3(aq), and glucose, C6H12O6(aq).

Hint 1 · the clue

Ask two questions for each: is it ionic (metal + nonmetal) or molecular? If molecular, is it a weak acid or a weak base, like ammonia, that forms only some ions?

Hint 2 · the next move

You must sort several solutes by electrolyte type: decide ionic, weak acid/base, or plain molecular for each.

Your path:

  1. Ionic (metal + nonmetal) → strong electrolyte
  2. Weak base like NH3 → weak electrolyte
  3. Molecular, not acid/base → nonelectrolyte
Answer

CaCl2: strong electrolyte; NH3: weak electrolyte; C6H12O6: nonelectrolyte.

Full worked solution

What you know: CaCl2, NH3, and C6H12O6 each dissolve in water. What you want: the electrolyte type of each.

  1. CaCl2 is a metal (Ca) plus a nonmetal (Cl), so it is ionic. It breaks apart completely: CaCl2 → Ca2+ + 2Cl−. It is a strong electrolyte.
  2. NH3 is molecular, but it is a weak base. Only some molecules react with water to form NH4+ and OH−; most stay as whole NH3 molecules. It is a weak electrolyte.
  3. Glucose has only C, H and O, so it is molecular. It is not an acid or a base, so it dissolves as whole, neutral molecules and forms no ions. It is a nonelectrolyte.

Check: Conductivity ranks them the same way: CaCl2(aq) conducts strongly, NH3(aq) weakly, and glucose(aq) not at all.

Watch out: Dissolving well is not the same as forming ions. Glucose dissolves easily but stays as molecules, and NH3 is mostly molecules even though it makes some ions.

On the periodic table: Calcium (Ca) is in Group 2, so it forms Ca²⁺. Chlorine (Cl) is in Group 17, so it forms Cl⁻.

Answer: CaCl2: strong electrolyte; NH3: weak electrolyte; C6H12O6: nonelectrolyte.

Watch out

Common net ionic equation mistakes