General Chemistry I · Chemical Process

Types of Chemical Reactions

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In 30 seconds
Why this matters
The college version
Eli explains
Worked example
Key takeaway
Study tools

In 30 seconds

Aqueous reactions fall into three classes: precipitation (two soluble salts swap partners to form an insoluble solid), acid-base (acid + base → salt + water), and oxidation-reduction (electrons transfer between species). predict precipitates; net ionic equations strip away to show only the species that change. In redox, states track electron gain and loss: the substance oxidized is the , and the substance reduced is the .

Why this matters

Acid-base neutralization explains how antacids work: bases such as calcium carbonate (CaCO3) or magnesium hydroxide (Mg(OH)2) neutralize stomach acid (HCl). Precipitation is used diagnostically — barium sulfate (BaSO4), deliberately insoluble, is swallowed for gastrointestinal X-ray imaging, and a visible in a urine or serum test can signal abnormal ions. Redox chemistry underlies cellular respiration, where glucose is oxidized and oxygen is reduced.

The college version

1. Precipitation Reactions and Solubility Rules

A forms an insoluble solid (the precipitate) from two aqueous solutions. To predict the product, "swap" the cations and anions of the reactants, then consult solubility rules to see which new combination is insoluble. Key rules (soluble unless noted):

Nitrate (NO3−) salts and alkali-metal (Group 1) and ammonium (NH4+) salts are always soluble.
Chlorides, bromides, and iodides are soluble except with Ag+, Pb2+, and Hg2^2+.
Sulfates (SO4^2−) are soluble except with Ba2+, Pb2+, Sr2+, and (slightly) Ca2+.
Hydroxides (OH−) and sulfides (S2−) are generally insoluble except Group 1 and NH4+.
Carbonates (CO3^2−) and phosphates (PO4^3−) are generally insoluble except Group 1 and NH4+.

2. Net Ionic Equations and Spectator Ions

There are three levels of ionic bookkeeping. The shows complete formulas; the splits every strong electrolyte into its aqueous ions; the cancels ions that appear unchanged on both sides (spectator ions), leaving only what reacts: $AgNO 3 (aq) + NaCl(aq) \to AgCl(s) + NaNO 3 (aq)$ $Ag + (aq) + NO 3 - (aq) + Na + (aq) + Cl - (aq) \to AgCl(s) + Na + (aq) + NO 3 - (aq)$ $Ag + (aq) + Cl - (aq) \to AgCl(s)$

3. Acid-Base Reactions (Neutralization)

An acid (H+ donor) reacts with a base (H+ acceptor, often OH−) to form a salt and water: $HCl(aq) + NaOH(aq) \to NaCl(aq) + H 2 O(l)$ The net ionic equation for any strong acid + strong base is the same: $H + (aq) + OH - (aq) \to H 2 O(l)$ Strong acids and bases ionize completely and are written as ions; weak acids (HC2H3O2) and weak bases (NH3) are written as intact molecules because they exist mostly undissociated.

4. Oxidation-Reduction (Redox) Reactions

Redox reactions transfer electrons. Assign oxidation states using these rules: free elements = 0; a monatomic ion = its charge; fluorine = −1; oxygen usually −2 (peroxides −1); hydrogen +1 with nonmetals but −1 with metal hydrides; the sum of oxidation states equals the overall charge. Oxidation is an increase in (loss of electrons); is a decrease (gain of electrons). The species oxidized is the reducing agent; the species reduced is the oxidizing agent.

How it works

Write the reactant formulas and swap cations and anions to predict products.
Assign state symbols using the solubility rules.
Balance the molecular equation using coefficients only.
Split strong electrolytes into ions to write the complete ionic equation.
Cancel spectator ions to obtain the net ionic equation.
For redox, assign oxidation states and identify what is oxidized and reduced.

Common confusions

Do not confuse	With	Difference
Oxidation state	Ionic charge	Oxidation state is assigned bookkeeping; ionic charge is the actual charge on an ion
Oxidizing agent	Substance oxidized	The oxidizing agent is itself reduced
Strong acid	Concentrated acid	Strong = fully ionized; concentrated = large amount of solute
Spectator ion	Precipitate	Spectators stay dissolved; the precipitate is the new solid
Solubility	Dissociation	Solubility is how much dissolves; dissociation is whether it forms ions

Memory aids

"OIL RIG" — Oxidation Is Loss, Reduction Is Gain (of electrons). For solubility: "Nitrates, Alkali metals, Ammonium always soluble" (NAA); "Cl, Br, I, SO4 soluble except with Ag, Pb, Hg, Ba, Sr."

Quick review

Topic Recap

Aqueous reactions divide into precipitation, acid-base, and redox. Solubility rules predict precipitates; net ionic equations remove spectator ions; acid-base reactions neutralize H+ and OH− to water; and redox transfers electrons, with oxidation states identifying what is oxidized and reduced.

Knowledge Check

Predict whether a precipitate forms when BaCl2 and Na2SO4 are mixed, and name it.
Write the net ionic equation for the reaction of AgNO3 with Na2S.
What are the spectator ions when KOH reacts with HNO3?
In the reaction 2 Na + Cl2 → 2 NaCl, what is oxidized and what is the oxidizing agent?
Why is a weak acid written as a molecule rather than as ions in a complete ionic equation?

Answers and Rationales

Yes — BaSO4 (barium sulfate) is insoluble (sulfate exception with Ba2+).
2 Ag+(aq) + S2−(aq) → Ag2S(s).
K+ and NO3− — unchanged on both sides; the net ionic equation is H+(aq) + OH−(aq) → H2O(l).
Sodium is oxidized (0 → +1), and Cl2 is the oxidizing agent (it is reduced, 0 → −1).
Because a weak acid exists mostly as intact molecules; the complete ionic equation shows species as they actually exist.

Eli explains

The same idea, in plain words

Explain it like I’m 10

Think of a double-date dance: Ag+ dances with NO3− and Na+ with Cl−. Mid-song, Ag+ and Cl− sprint to each other and form a solid so stable they leave the floor (a precipitate). The lonely Na+ and NO3− keep dancing unchanged — spectator ions, present but never part of the action.

For redox, an electron is like a coin handed over: the giver loses it (is oxidized) and is the reducing agent; the receiver gains it (is reduced) and is the oxidizing agent. It stops being exact because electrons are not handed over one at a time in a visible exchange — oxidation states are a bookkeeping tool for where electron density shifts, and the transfer can be partial (as in polar covalent bonds).

Simple Example

Mixing silver nitrate and sodium chloride: $AgNO 3 (aq) + NaCl(aq) \to AgCl(s) + NaNO 3 (aq)$ AgCl is the white precipitate. The net ionic equation is: $Ag + (aq) + Cl - (aq) \to AgCl(s)$ Na+ and NO3− are spectator ions and are omitted.

Worked example

Worked example — precipitation: Mix aqueous lead(II) nitrate and potassium iodide. Predict products and write the net ionic equation.

Swap partners: Pb2+ + I− → PbI2; K+ + NO3− → KNO3.
Solubility: PbI2 is insoluble (iodide exception with Pb2+); KNO3 is soluble (nitrate, potassium).
Molecular: Pb(NO3)2(aq) + 2 KI(aq) → PbI2(s) + 2 KNO3(aq).
Net ionic: Pb2+(aq) + 2 I−(aq) → PbI2(s). Spectators: K+ and NO3−.

Worked example — redox: $Zn(s) + CuSO 4 (aq) \to ZnSO 4 (aq) + Cu(s)$ Zn: 0 → +2 (oxidized, so Zn is the reducing agent). Cu: +2 → 0 (reduced, so Cu2+ is the oxidizing agent). Common setup error: assigning the oxidizing agent to the atom that gets oxidized — the oxidizing agent is itself reduced.

Key takeaways

High yield: All nitrates, and all Group 1 and NH4+ salts, are soluble.
High yield: The net ionic equation for a strong acid + strong base is always H+(aq) + OH−(aq) → H2O(l).
High yield: The oxidizing agent is reduced; the reducing agent is oxidized (OIL RIG).
High yield: Spectator ions appear unchanged on both sides and are omitted from net ionic equations.
Weak acids and bases are written as molecules, not ions, in ionic equations.
Precipitation, acid-base, and redox can overlap.
Balance with coefficients only — never change subscripts.

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Practice General Chemistry I

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Study toolsYou’ll learn to · Key vocabulary

You’ll learn to

Use solubility rules to predict whether a precipitate will form when two solutions are mixed.
Write molecular, complete ionic, and net ionic equations, and identify spectator ions.
Recognize and complete acid-base (neutralization) reactions, distinguishing strong from weak acids and bases.
Assign oxidation states and identify the oxidizing and reducing agents in a redox reaction.

Key vocabulary

Precipitation reaction: Mixing solutions that produces an insoluble solid
Precipitate: The insoluble solid that forms
Solubility rules: Guidelines for which salts dissolve
Molecular equation: Equation with full neutral formulas
Complete ionic equation: Equation splitting strong electrolytes into ions
Net ionic equation: Equation showing only reacting species
Spectator ions: Ions unchanged on both sides
Neutralization reaction: Acid + base → salt + water
Oxidation: Loss of electrons / higher oxidation state
Reduction: Gain of electrons / lower oxidation state
Oxidation state: Bookkeeping charge assigned to an atom
Oxidizing agent: Species that is reduced (gains electrons)
Reducing agent: Species that is oxidized (loses electrons)

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