THE LESSON LIBRARY / CHEMISTRY
Chemistry, explored.
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Physical Chemistry Problem Solving: Integrated Review
This unit has covered gases, solutions, thermochemistry, equilibria, electrochemistry and kinetics. The topics look different, but almost every calculation rests on three…
Explore lesson ChemistryLessonPhysical Constants for Chemistry
Physical constants connect the molecular and macroscopic descriptions of chemistry. Avogadro's constant converts counts to moles; the Faraday constant converts electron moles to…
Explore lesson ChemistryLessonPhysical or Chemical? Deciding Between Them
Some changes are easy to classify: melting ice is physical, burning paper is chemical. Others are harder. Is a firework's bang physical? Is the fading of a pair of jeans…
Explore lesson ChemistryLessonPhysical Properties of Aldehydes and Ketones
Aldehydes and ketones have polar C=O groups. That gives stronger attractions than many hydrocarbons of similar mass and allows their oxygen atoms to accept hydrogen bonds from…
Explore lesson ChemistryLessonPhysical Properties of Alkanes — Carbon Compounds: Introduction
Methane is a gas that boils at −162 °C, petrol is a runny liquid that evaporates quickly, and candle wax is a solid. Yet all three are alkanes, made of the same kind of molecule…
Explore lesson ChemistryLessonPhysical Properties of Alkanes — Hydrocarbons
Alkanes have nonpolar or nearly nonpolar C–C and C–H bonds, so their physical behavior is dominated by dispersion forces rather than strong permanent dipoles or hydrogen bonding.…
Explore lesson ChemistryLessonPhysical Properties of Carboxylic Acids
Carboxylic acids often boil at higher temperatures than comparably sized aldehydes, ketones and even many alcohols. Their –COOH groups can both donate and accept hydrogen bonds…
Explore lesson ChemistryLessonPhysical Properties of Isotopes
Isotopes can behave similarly in chemical bonding and still differ in physical measurements. Their different masses influence molecular speeds, vibrations and sometimes density…
Explore lesson ChemistryLessonPhysical Properties of Metals — Metals and Non-metals
Many metals look shiny, carry electric current and can be shaped without shattering. These traits explain their use in wires, tools and sheets, but they are tendencies rather…
Explore lesson ChemistryLessonPhysical Properties of Metals — Metals, Reactivity Series and Metallurgy Basics
Metals are often introduced as shiny, strong, dense solids that conduct heat and electricity. Those words describe useful tendencies, but real metals vary. A clean sodium surface…
Explore lesson ChemistryLessonPhysical Properties of Metals — The Periodic Table: Basics
Think of a saucepan, a copper wire, a gold ring and a steel bridge. They look and behave very differently from wood, plastic or glass, yet they share a set of features that make…
Explore lesson ChemistryLessonPhysical Properties of Non-metals — Metals and Non-metals
Many non-metals contrast with familiar metals: they may be gases, and their solids are often poor electrical conductors or brittle. Yet “non-metal” is a broad category that…
Explore lesson ChemistryLessonPhysical Properties of Non-metals — The Periodic Table: Basics
Oxygen in the air, the carbon in a pencil, the sulfur in a volcano's yellow crust and the chlorine used to treat water are all non-metals. Although there are far fewer non-metals…
Explore lesson ChemistryLessonPhysical Properties of Organohalides
Organohalides can be gases, liquids, or solids depending on their structure and size. Halogen substitution often changes boiling point, density, and solubility, which affects…
Explore lesson ChemistryLessonPhysisorption and Chemisorption
Nitrogen may attach weakly to a cold solid, while hydrogen can dissociate and bind to a clean metal surface. Both are adsorption, yet their energies and consequences differ. The…
Explore lesson ChemistryLessonPi Bond Orders and Electron Densities
Hückel eigenvalues describe pi orbital energies, while eigenvectors describe how each orbital spreads over atoms. To connect the model to local chemical questions, the…
Explore lesson ChemistryLessonPig Iron and Steel
Reducing iron oxide in a blast furnace produces crude iron, not a finished steel grade. The molten iron dissolves carbon and carries impurities. Further processing adjusts its…
Explore lesson ChemistryLessonPinacol Rearrangement
Two neighbouring alcohol groups can become one carbonyl while the carbon skeleton rearranges. In the pinacol rearrangement, acid helps one OH leave as water; a group on the…
Explore lesson ChemistryLessonPinch Thinking and Combined Heat and Power
A large chemical site has many streams that need cooling and many others that need heating. Connecting one hot product to one cold feed can save energy, but a local match may…
Explore lesson ChemistryLessonPlacing Bonds and Lone Pairs
After choosing a skeleton, the next Lewis task is to spend the electron budget exactly. Start with one pair for each provisional bond, give terminal atoms the electrons they…
Explore lesson ChemistryLessonPlanar and Volume Defects
Point defects and dislocations are not the only deviations from an ideal infinite crystal. A polycrystalline solid is a patchwork of grains whose atomic orientations differ.…
Explore lesson ChemistryLessonPlanning a Copper Electroplating Cell
A copper-plating plan specifies the object, source of copper ions, electrical connections and bath. A diagram with copper sulfate solution but reversed electrode labels can…
Explore lesson ChemistryLessonPlanning a Dilution
Planning a dilution begins with the target: a required concentration and final volume. The stock aliquot must contain exactly the solute amount that the final solution needs.…
Explore lesson ChemistryLessonPlanning a Multi-Step Separation
Real mixtures rarely contain just two substances. A sample from a beach might hold sand, salt, iron filings and seawater; a recycling plant must sort metals, plastics and paper.…
Explore lesson ChemistryLessonPlanning Three- and Four-Step Conversions
Three- and four-step conversions are not solved by writing a row of reagent names from memory. Each arrow creates the substrate for the next arrow, and every intermediate must…
Explore lesson ChemistryLessonPlanning Two-Step Conversions
A two-step conversion is solved by finding one intermediate that the start can make and the target can arise from. This may sound simple, but the intermediate must have the…
Explore lesson ChemistryLessonPlaster of Paris and Gypsum
Gypsum and plaster of Paris contain the same calcium sulfate framework but different amounts of crystal water. Gypsum is CaSO₄·2H₂O; plaster of Paris is the hemihydrate…
Explore lesson ChemistryLessonPlasticisers, Copolymers and the Fox Equation
A polymer's glass transition can be adjusted without synthesising a completely new homopolymer. Plasticisers, miscible blends and copolymer composition alter how easily chain…
Explore lesson ChemistryLessonPlastics and Litter in the Environment
Plastics are cheap, light, strong, waterproof and easy to shape, which is why they are used for everything from drinks bottles to car parts. But the same properties that make…
Explore lesson ChemistryLessonPoint Defects Overview
Real crystals are not perfect infinite repetitions. They contain defects such as missing atoms, extra atoms between regular sites and replacement atoms. Point defects involve a…
Explore lesson ChemistryLessonPoint Groups and Symmetry Labels for d Orbitals
The familiar t₂g/e_g and e/t₂ names are not arbitrary labels for “low” and “high.” They are symmetry labels describing how groups of d orbitals transform under rotations and…
Explore lesson ChemistryLessonPolar Covalent Bonds
Hydrogen chloride and water contain bonds whose electrons are shared unequally. Such polar covalent bonds have partial positive and negative ends. To predict the behaviour of an…
Explore lesson ChemistryLessonPolarisation and Fajans' Rules
The ideal ionic model treats ions as rigid charged spheres, but real electron clouds can distort. A small, highly charged cation pulls on the electron density of a nearby anion.…
Explore lesson ChemistryLabPolarisation and Fajans’ rules
A small, highly charged cation distorts the electron cloud of an anion and adds covalent character (Fajans’ rules).
Explore lesson ChemistryLessonPolarisation in Ionic Compounds
An ionic formula uses whole charges, such as Li⁺ and I⁻, but the electron cloud of a negative ion is not a rigid sphere. A nearby positive ion attracts and distorts that cloud.…
Explore lesson ChemistryLessonPolarity and Force Problem Set
Two familiar questions are often combined: Is a molecule polar, and which attractions hold its molecules near one another? The first depends on three-dimensional vector addition.…
Explore lesson ChemistryLessonPolarity and Solubility
Chemists often say “like dissolves like” to anticipate which solvent may dissolve a substance. That phrase points toward compatible intermolecular interactions, but it is only a…
Explore lesson ChemistryLessonPolarization Functions
Atoms in molecules do not retain spherical or isolated-atom electron distributions. A bond pulls density in one direction; a lone pair points into another; an electric field can…
Explore lesson ChemistryLessonPollutants from Burning Fuels
A perfectly pure hydrocarbon burning completely would give only carbon dioxide and water. Real fuels and real engines are messier. Coal and crude oil contain impurities, air is…
Explore lesson ChemistryLessonPolyatomic Ions and Their Valencies
Sodium hydroxide, potassium nitrate, copper sulfate, calcium carbonate, ammonium chloride: each contains a small group of atoms that travels as a team. These groups are…
Explore lesson ChemistryLessonPolyhydric Alcohols
A polyhydric alcohol contains more than one alcohol hydroxyl group. Ethane-1,2-diol has two, and glycerol has three. Multiple OH sites allow extensive hydrogen bonding and…
Explore lesson ChemistryLessonPolymer Architecture
Two samples can have exactly the same repeat unit and similar molar mass yet behave very differently because their chains are connected in different ways. The way repeat units…
Explore lesson ChemistryLessonPolymer Chains in Space
A polymer chain is not normally a fully stretched line. Rotation about its backbone bonds lets it sample many shapes, often described statistically as a coil. Coil dimensions…
Explore lesson ChemistryCollectionPolymer Chemistry
Study Polymer Chemistry with 40 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonPolymer Chemistry: Unit Review
Polymer chemistry links synthesis to chain length, architecture, spatial packing and useful properties. The same repeat unit can make very different materials when chain-growth…
Explore lesson ChemistryLessonPolymer Fundamentals
The word polymer describes a family of long covalent chains, not a single molecule with one exact formula. A plastic pellet can contain chains of many lengths even when every…
Explore lesson ChemistryLessonPolymer Mechanical Properties
A polymer can be brittle, ductile or rubbery depending on chemistry, molar mass, crystallinity, temperature and loading speed. Stress–strain curves reveal how it deforms, while…
Explore lesson ChemistryLessonPolymer Molecular-Mass Averages
A polymer sample rarely consists of chains all the same length. Reporting “the molecular weight” without saying which average can conceal a broad distribution. Number-average…
Explore lesson ChemistryLessonPolymer Nomenclature and Repeat Units
Polymer names can be confusing because the same material may have a systematic name, a common name, an abbreviation and a trade name. Poly(tetrafluoroethene), PTFE and Teflon all…
Explore lesson ChemistryLessonPolymer Thermal Behavior
A plastic can soften gradually without a sharp melting point, while another shows both a softening region and a distinct crystal-melting event. These observations reflect…
Explore lesson ChemistryLessonPolymeric and Chain Structures
Some inorganic formulas represent only the smallest ratio of atoms, not an isolated molecule. Silicates can form chains, sheets or networks by sharing oxygen corners. Phosphate…
Explore lesson ChemistryLabPolymerisation
Polymers form by addition (chain growth) or condensation (step growth).
Explore lesson ChemistryLessonPolymers, Sustainability and Recycling
Polymer design also determines what happens after a product is used. A material's recyclability or biodegradability cannot be inferred from a green label or one functional group…
Explore lesson ChemistryLessonPolymorphism and Allotropy
One chemical composition can appear in more than one solid structure. Different crystal forms of a compound are polymorphs, while different forms of an element are allotropes.…
Explore lesson ChemistryLessonPolyprotic Acid Equilibria
An acid with more than one transferable proton does not usually release every proton in one identical step. Each proton transfer has its own conjugate pair and equilibrium…
Explore lesson ChemistryLessonPolyprotic Acid Titration Stages
When a monoprotic weak acid is titrated with sodium hydroxide, the pH curve shows one buffer region and one steep rise. A polyprotic acid carries more than one ionisable proton…
Explore lesson ChemistryLessonPolyprotic Acids and Stepwise Ka Values
Many important acids can give away more than one proton: sulfuric acid, carbonic acid, oxalic acid, phosphoric acid and citric acid are all examples. Such acids are called…
Explore lesson ChemistryLessonPolyprotic Buffer Regions
A polyprotic acid is not one buffer but several. Phosphoric acid, with three removable protons, offers three separate regions of strong buffering, each centred on a different…
Explore lesson ChemistryLessonPolysaccharides
Starch, glycogen and cellulose are all built from glucose, yet their roles are very different. Plants store starch, animals store glycogen, and plants use cellulose in cell…
Explore lesson ChemistryLessonPopulation Analysis and Partial Charges
An electron density is spread across an entire molecule. A drawing that places a number such as +0.24 on one atom is a convenient summary, but nature does not mark a boundary…
Explore lesson ChemistryLessonPorous Electrode Architecture
An active material with excellent capacity does little in a cell if ions cannot reach it or electrons cannot leave it. A practical electrode is a porous composite of active…
Explore lesson ChemistryLessonPorous Electrodes and Transmission-Line Behaviour
A battery electrode is usually a porous composite, not one flat interface. Electrons travel through active solids, carbon and a current collector; ions travel through…
Explore lesson ChemistryLessonPorous Nanomaterials
A porous nanomaterial can contain an enormous internal interface in a small external volume. That interface supports adsorption, catalytic reactions and electrochemical charge…
Explore lesson ChemistryLessonPorphyrins and the Heme Group
Heme is one of nature's most versatile cofactors. The same iron porphyrin carries oxygen in blood, passes electrons along respiratory chains and activates O₂ to oxidise…
Explore lesson ChemistryLessonPositive Deviations from Raoult's Law
An ideal mixture follows a straight Raoult-law pressure line between pure-component endpoints. Some real mixtures have higher vapour pressure than that line at intermediate…
Explore lesson ChemistryLessonPositive Ions from Metal Atoms
Sodium, magnesium and aluminium commonly appear in compounds as positive ions. Their neutral atoms have different numbers of outer electrons, so their usual charges differ.…
Explore lesson ChemistryLessonPost-Hartree–Fock Correlation Methods
Hartree–Fock optimizes one Slater determinant and includes exchange, but leaves out much correlated electron motion. Several wavefunction methods add that missing behavior in…
Explore lesson ChemistryLessonPotassium and Calcium Configurations
Argon has 18 electrons arranged through 3p⁶. Potassium and calcium add the nineteenth and twentieth electrons to 4s, not to 3d, in their ordinary neutral ground states. This is a…
Explore lesson ChemistryLessonPotassium Compounds and Plant Nutrients
Potassium metal is highly reactive, but potassium in common salts is present as K⁺. KCl, K₂SO₄ and KNO₃ can all supply potassium ions when they dissolve, yet each also supplies a…
Explore lesson ChemistryLessonPotassium Dichromate as an Oxidant
Potassium dichromate K₂Cr₂O₇ supplies dichromate ions, Cr₂O₇²⁻, in water. The chromium is formally +6, and in acidic solution dichromate can accept electrons to produce…
Explore lesson ChemistryLessonPotassium Permanganate as an Oxidant
Potassium permanganate KMnO₄ supplies purple MnO₄⁻ ions with formal Mn(VII). It is a strong oxidant in many contexts, but its reduction product is not always Mn²⁺. Acidic…
Explore lesson ChemistryLabPotential energy surface explorer
A potential energy surface: valleys are stable molecules, passes are transition states.
Explore lesson ChemistryLessonPotential Energy Surfaces
Collision theory asks whether molecules meet with enough energy and suitable orientation. A potential-energy surface explains why orientation and geometry matter. It maps the…
Explore lesson ChemistryLessonPotential Energy Surfaces and Dynamics: Unit Review
A reaction diagram begins with reactants, a barrier and products, but research-level mechanism work needs several layers of evidence. A potential-energy surface supplies minima…
Explore lesson ChemistryCollectionPotential Energy Surfaces and Reaction Dynamics
Study Potential Energy Surfaces and Reaction Dynamics with 40 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonPotential Energy Surfaces: The Research Picture
A reaction diagram in a textbook often shows energy against one horizontal coordinate, rising to a transition structure and falling to product. Research calculations start from a…
Explore lesson ChemistryLessonPotentiometric Titrations
A titration need not rely on a colored indicator. If an electrode responds to a species whose activity changes during reaction, recording potential after each titrant addition…
Explore lesson ChemistryLessonPre-Equilibrium Approximation — Advanced Electrochemistry and Kinetics
Some mechanisms begin with a fast reversible step that sets up an equilibrium, followed by a much slower step that siphons off a little of the equilibrium mixture to make…
Explore lesson ChemistryLessonPre-Equilibrium Approximation — Chemical Kinetics
A mechanism may begin with a fast reversible association that establishes an approximately stable ratio among reactants and an intermediate. If a later step forms product more…
Explore lesson ChemistryLessonPrecipitation After Mixing Solutions
When two ionic solutions are mixed, a precipitate may form if their combined free-ion product exceeds Ksp. The first arithmetic step is dilution: each stock solution now occupies…
Explore lesson ChemistryLabPrecipitation and Ksp
Mix two ionic solutions. A precipitate forms only when the ionic product Q exceeds Ksp.
Explore lesson ChemistryLessonPrecipitation as Salt Preparation
Some salts are easiest to prepare by bringing their ions together in solution so the target product precipitates. This strategy differs from crystallising a soluble salt: the…
Explore lesson ChemistryLessonPrecipitation Reactions
Two clear solutions can produce a cloudy solid when an ion pair has low solubility. That is precipitation. At the formula level, many examples fit double displacement; at the…
Explore lesson ChemistryLessonPrecipitation Stoichiometry
A precipitate forms when dissolved ions combine into a solid under suitable conditions. Its amount follows a balanced equation, but measured solution volumes must first become…
Explore lesson ChemistryLessonPrecipitation Titrations: Argentometry
Silver ions form sparingly soluble halides, making precipitation a basis for chloride and related analyses. The central reaction for chloride is Ag⁺ + Cl⁻ → AgCl(s), but a…
Explore lesson ChemistryLessonPrecipitation, Nucleation and Crystal Growth
Precipitation gravimetry requires more than making a solid appear. The size and cleanliness of the particles affect whether they can be filtered and weighed reliably. Mixing a…
Explore lesson ChemistryLessonPrecipitation: Rain, Snow and Hail
Clouds contain huge amounts of water, yet many clouds drift past without a single drop falling. For water to return to the ground, the tiny droplets in a cloud must grow large…
Explore lesson ChemistryLessonPrecision and Significant Figures in Stoichiometry
Stoichiometric calculations can yield many calculator digits, but not all are supported by the data. A measured mass or volume has finite precision. The balanced coefficients are…
Explore lesson ChemistryLessonPrecision, Accuracy and Bias
A laboratory can make nearly identical measurements that are all wrong, or scattered measurements whose average lies near the true value. These situations require different…
Explore lesson ChemistryLessonPredicting Absorption Wavelengths of Dyes
A conjugated dye can absorb visible light because one of its electrons can be promoted between molecular energy levels by a visible photon. A simple particle-in-a-box picture…
Explore lesson ChemistryLessonPredicting an Unfamiliar Element
Periodic classification is most valuable when it helps us reason about an element whose details we do not yet know. Position suggests electron configuration, common bonding…
Explore lesson ChemistryLessonPredicting Bond Type from the Periodic Table
The periodic table can turn an unfamiliar formula into a manageable first prediction. A metal and non-metal often suggest ions; non-metals often suggest shared electrons; a metal…
Explore lesson ChemistryLessonPredicting Deposited Metal Amount
A charge meter does not directly report grams of metal. To predict an ideal deposit, convert charge to electron moles, use the electrode half-reaction to find metal moles, and…
Explore lesson ChemistryLessonPredicting Displacement Reactions
Suppose a strip of iron is added to zinc sulfate solution, and a strip of zinc is added to iron(II) sulfate solution. The same two metals appear in both trials, but only one…
Explore lesson ChemistryLessonPredicting Electrocyclic Stereochemistry
The statement “four electrons rotate conrotatorily under heat” is a starting rule, not the final product. A substituted diene or triene has groups at its terminal atoms that…
Explore lesson ChemistryLessonPredicting Ion Charges from Group Number
The periodic table can help you predict the ions in many simple salts without memorising every compound separately. The key is the recurring number of valence electrons. Group…
Explore lesson ChemistryLessonPredicting Products of Combination Reactions
The one-product pattern of combination does not tell us the product's exact formula. Ion charges can predict many metal–non-metal formulas, while known molecular composition…
Explore lesson ChemistryLessonPredicting Products of Decomposition Reactions
Decomposition problems often ask for products before any balancing can begin. Familiar patterns help: a specified metal carbonate may give an oxide and CO₂, hydrogen peroxide…
Explore lesson ChemistryLessonPredicting Products of Double Displacement
Predicting a double displacement product requires two decisions. First, exchange cation-anion partners and write correct neutral formulas. Second, ask whether anything actually…
Explore lesson ChemistryLessonPredicting Properties from Position
You have probably never held a piece of rubidium or seen astatine, and very few chemists have. Yet you can say a great deal about them without ever opening a bottle. The periodic…
Explore lesson ChemistryLessonPredicting Reaction Behaviour from Position
Periodic position can suggest that potassium may form +1 salts or chlorine may displace bromide, but it cannot supply every product and rate without context. The strongest…
Explore lesson ChemistryLessonPredicting Redox Spontaneity
A positive cell potential indicates that the written redox reaction can deliver electrical work in a galvanic arrangement under the stated conditions. A negative potential favors…
Explore lesson ChemistryLessonPredicting Simple Compounds from Groups
Periodic groups can suggest simple ion charges and therefore compound formulas. Calcium in group 2 commonly forms Ca²⁺, while chlorine in group 17 commonly forms Cl⁻; the neutral…
Explore lesson ChemistryLessonPredicting Simple Ion Charges
A chemical formula is difficult to predict unless the ion charges are known. The periodic table gives reliable first clues for many simple main-group ions: group-one metals…
Explore lesson ChemistryLessonPredicting Spin State from Δo and P
Ligand names provide clues about spin state, but a numerical question is settled by an energy comparison. For octahedral d⁴ through d⁷, placing an electron into e_g costs Δₒ…
Explore lesson ChemistryLessonPredicting State from Melting and Boiling Points
Is bromine a solid, a liquid or a gas on a summer's day? What about oxygen on the Moon's dark side, or iron in a furnace? You do not need to see a substance to answer. If you…
Explore lesson ChemistryLessonPredicting Unknown Elements: Mendeleev's Successes
Any idea can be made to fit facts that are already known. The real test of a scientific theory is whether it can predict something nobody has yet seen. In 1871 Dmitri Mendeleev…
Explore lesson ChemistryLessonPredicting Whether Displacement Will Occur
The most important displacement question is sometimes whether a reaction happens at all. A balanced proposed equation can still be chemically unsupported. To predict direction…
Explore lesson ChemistryLessonPrefixes in Compound Names
Carbon and oxygen form two different gases. One, carbon dioxide, is the gas you breathe out. The other, carbon monoxide, is a highly toxic gas produced when fuels burn in too…
Explore lesson ChemistryLessonPreliminary Tests on an Unknown Salt
Before selective reagents are considered, an unknown salt already offers clues: crystal colour, texture, behaviour in water and reported changes on heating. These preliminary…
Explore lesson ChemistryLessonPreparation by Alcohol Halogenation
Alcohols are convenient starting materials for alkyl halides because a hydroxyl group marks the carbon where a halogen should appear. Direct departure of OH⁻ is usually…
Explore lesson ChemistryLessonPreparation by Alcohol Oxidation
Alcohol oxidation is a common conceptual route to aldehydes and ketones. A primary alcohol can become an aldehyde; a secondary alcohol can become a ketone. The same carbon…
Explore lesson ChemistryLessonPreparation by Alkene Addition
Alkenes offer a direct route to haloalkanes because their C=C π bond can be replaced by new σ bonds. Addition of HX gives a monohaloalkane, while addition of X₂ gives a vicinal…
Explore lesson ChemistryLessonPreparation of Alcohols by Hydration
An alkene can become an alcohol by adding the elements of water across its C=C bond. Acid-catalyzed hydration is a common conceptual route, often placing OH at the more…
Explore lesson ChemistryLessonPreparation of Alkenes
Alkenes are commonly prepared by elimination: two groups leave from neighboring carbons while a C=C bond forms between them. Dehydration of an alcohol removes water, and…
Explore lesson ChemistryLessonPreparation of Alkynes
An alkyne can be built by creating a triple bond from a suitably placed dihalide through two eliminations. A different synthetic strategy starts with a terminal alkyne, removes…
Explore lesson ChemistryLessonPreparation of Aryl Halides
An aryl halide has halogen directly attached to an aromatic ring. Direct ring halogenation replaces a ring hydrogen, unlike alkene addition, which consumes a π bond. A second…
Explore lesson ChemistryLessonPreparing a Soluble Salt by Titration
Sodium chloride, potassium nitrate and ammonium sulfate are all soluble salts, and so are the bases that contain their metal or ammonium ion: sodium hydroxide, potassium…
Explore lesson ChemistryLessonPreparing a Soluble Salt from an Insoluble Base
Many useful salts, such as copper(II) sulfate, zinc sulfate and magnesium chloride, dissolve in water. To make a pure, dry sample of one of them we need a method that leaves…
Explore lesson ChemistryLessonPreparing a Standard Solution
To make a solution with known molarity, it is not enough to weigh the right solid and add an approximate amount of water. The solute amount must be known, dissolved material must…
Explore lesson ChemistryLessonPreparing Amines by Reduction
Substitution of alkyl halides is not the only way to create amines. A nitro group attached to an aromatic ring can be reduced to an amino group, providing a common route to…
Explore lesson ChemistryLessonPreparing Amines by Substitution
Ammonia can act as a nitrogen nucleophile toward a suitable alkyl halide, replacing the halide and forming a carbon–nitrogen bond. This offers a route to a primary amine, but the…
Explore lesson ChemistryLessonPreparing an Insoluble Salt by Precipitation
Some salts do not dissolve in water. Barium sulfate, silver chloride and lead(II) iodide are examples. We cannot make these by crystallising a solution, because they will not…
Explore lesson ChemistryLessonPreparing Buffers by Partial Neutralisation
A buffer need not be made by mixing separate acid and salt bottles. A weak acid HA can be partly neutralised by a measured amount of strong base, creating A⁻ while leaving some…
Explore lesson ChemistryLessonPreparing Buffers from Weak Base and Strong Acid
A weak base B can be converted partly to its conjugate acid BH⁺ by adding a measured amount of strong acid. The mixture of B and BH⁺ can buffer pH. The calculation mirrors…
Explore lesson ChemistryLessonPreparing Carboxylic Acids by Oxidation
The most common laboratory route to a carboxylic acid is oxidation. A primary alcohol can be oxidised first to an aldehyde and then, if the conditions allow, on to the carboxylic…
Explore lesson ChemistryLessonPreparing Colloids
Making a colloid requires particles in an intermediate size range and a way to keep them from joining into larger aggregates. Two broad routes reach that range from opposite…
Explore lesson ChemistryLessonPreparing Salts by Acid–Base Reaction
Making a salt begins with its target ions. An acid can provide the anion and a base the cation; their reaction may form water as a second product. The equation alone is not a…
Explore lesson ChemistryLessonPreparing Salts with Metals or Carbonates
An acid need not react only with a hydroxide to form a salt. Suitable metals can replace acid hydrogen and release H₂, while carbonates consume acid and release CO₂ along with…
Explore lesson ChemistryLessonPressure and Volume Changes
Compressing a gaseous equilibrium mixture changes the partial pressures of all gas species before reaction readjustment. A common rule says compression favors the side with fewer…
Explore lesson ChemistryLessonPressure Changes in a Rigid Reactor
Gas pressure in a rigid vessel can change because a reaction alters the number of gas molecules, because the temperature changes, or both. A pressure rise therefore does not by…
Explore lesson ChemistryLessonPressure Equilibrium Constant Kp
Gas equilibria are often measured through pressures rather than concentrations. Kp uses the partial pressures of gaseous species in the balanced reaction. Pure solids and liquids…
Explore lesson ChemistryLessonPressure from Particle Collisions
A gas presses on every wall of its container, not just the bottom. Its particles move in many directions and repeatedly collide with boundaries. Each collision transfers…
Explore lesson ChemistryLessonPressure-Temperature Gas Law
Heating a gas trapped in a rigid sealed vessel cannot make its volume grow. Instead, its pressure rises. For a fixed amount of gas close to ideal behavior, pressure is…
Explore lesson ChemistryLessonPressure-Volume Work
When a gas pushes a piston, it can transfer energy to the surroundings as pressure-volume work. Under the chemistry sign convention, expansion work is negative for the gas…
Explore lesson ChemistryLessonPreventing Corrosion by Barriers
One way to slow corrosion is to keep oxygen, water and corrosive solution away from a metal surface. Paint, polymer coatings and some adherent oxide layers act as barriers. Their…
Explore lesson ChemistryLessonPreventing Rust with Barriers — Metals and Non-metals
Rusting needs water and oxygen to reach iron. A barrier coating can interrupt that contact. Paint on a gate, grease on a tool and plastic around a wire all use this principle.…
Explore lesson ChemistryLessonPreventing Rust with Barriers — Physical and Chemical Changes
If rusting needs both water and oxygen, then the simplest way to stop it is to keep them away from the iron. That is the idea behind barrier methods: covering the metal with a…
Explore lesson ChemistryLessonPrimary and Secondary Valence in Werner Theory
Before modern orbital models, cobalt–ammonia compounds posed a puzzle: compounds with the same metal and apparent combining power released different numbers of chloride ions in…
Explore lesson ChemistryLessonPrimary Aromatic Amines and Nitrous Acid
A primary aromatic amine such as aniline can be converted conceptually into an arenediazonium ion, Ar–N₂⁺, through reaction with nitrous-acid chemistry under controlled cold…
Explore lesson ChemistryLessonPrimary Cells: Zinc–Manganese Dioxide Chemistry
Common disposable cylindrical cells often use zinc as the negative electrode material and manganese dioxide as a positive-electrode reactant. Their approximate 1.5 V class is…
Explore lesson ChemistryLessonPrimary Standards and Standardisation
A titration gives analyte amount only when the titrant concentration is known. Preparing a solution by weighing a reagent and filling a flask may not be enough: the reagent could…
Explore lesson ChemistryLessonPrimary, Review and Reference Sources
Scientific claims need different sources. A definition of an analytical term is best checked against an authoritative terminology reference; a proposed mechanism needs the…
Explore lesson ChemistryLessonPrincipal Quantum Number
The principal quantum number n is the first label of an atomic orbital. It takes positive integers 1, 2, 3, and so on. It organizes orbitals into shells and helps describe their…
Explore lesson ChemistryLessonPrincipal Shells and Subshells
An atom's electron arrangement has layers of organisation. A shell is labelled by a positive integer n; within it are subshells such as s and p; within a subshell are individual…
Explore lesson ChemistryLessonPrinciple 1: Prevent Waste
The first green-chemistry principle says it is better to prevent waste than to treat or clean it up after creation. That statement sounds simple, but applying it requires knowing…
Explore lesson ChemistryLessonPrinciples of Chromatography
Chromatography separates components of a mixture by letting them travel at different speeds through a system with a moving fluid and a stationary material. A molecule that spends…
Explore lesson ChemistryLessonPrinciples of Extractive Metallurgy
Extracting a metal from rock is a sequence of decisions, not a single reduction equation. Ore must often be concentrated, converted into a tractable chemical form, reduced or…
Explore lesson ChemistryLessonPrinciples of Gravimetric Analysis
Gravimetric analysis measures mass rather than titrant volume or instrumental light response. The analyte may be isolated directly, converted into a sparingly soluble solid, or…
Explore lesson ChemistryLessonPrinciples of Industrial Electrolysis
Industrial electrolysis turns electricity into chemical change. It can make hydrogen, chlorine, sodium hydroxide, refined metals and other products, depending on electrolyte and…
Explore lesson ChemistryLessonPrinciples of Metabolism
Metabolism is a network of connected chemical reactions, not a collection of independent arrows. A nutrient may supply carbon skeletons, ATP, reducing equivalents or all three.…
Explore lesson ChemistryLessonPrinciples of Photochemistry: Absorbing Light
Photochemistry begins with energy arriving in discrete photons. A molecule reacts only after a suitable absorbing species receives light, but many absorbed photons are lost…
Explore lesson ChemistryLessonPrinciples of Titrimetry
A titration determines the amount of an analyte by reacting it with a known amount of another substance. The analyst adds titrant until an indicator or instrument signals the end…
Explore lesson ChemistryCollectionPrivacy
Understand local device storage, optional services and privacy information for the Kalviyogi ChemLab student release.
Explore lesson ChemistryLessonProbability Distributions in the Box
Solving the Schrödinger equation for the particle in a box gives wavefunctions and energies, but a chemist really wants to know something more physical: *where is the particle?*…
Explore lesson ChemistryLessonProbing Electrode Kinetics Experimentally
Electrode kinetics cannot be read directly from one current value. Voltammetry changes potential and records current, while impedance spectroscopy perturbs a chosen state…
Explore lesson ChemistryLessonProbing Surfaces: Spectroscopy and Microscopy
A catalyst may have enormous measured area, yet its useful chemistry depends on the topmost atoms, defects and adsorbates. No one instrument reveals everything about a surface.…
Explore lesson ChemistryLessonProblem Solving with Acids, Bases and Salts
Longer exam questions rarely test one idea on its own. A single question might ask you to choose a method for making a salt, write its equation, calculate a concentration from…
Explore lesson ChemistryLessonProblem Solving with Atomic Structure
Atomic-structure problems become more demanding when several familiar ideas appear together. A question may give an average mass, an ion's electron count and an isotope label…
Explore lesson ChemistryLessonProblem Solving with Atoms and Molecules
Exam questions rarely test one idea in isolation. A single question might ask you to count atoms in a formula, identify whether a substance is an element or compound, find its…
Explore lesson ChemistryLessonProblems with Rutherford's Model
The nuclear model explained why most alpha particles passed through a foil while a few were strongly deflected. It did not, by itself, explain how electrons remained arranged…
Explore lesson ChemistryLessonProcess Economics: Yield, Rate and Cost
Industrial chemistry is judged by how reliably it makes useful material, not by yield alone. A route with nearly complete conversion may require an enormous reactor, expensive…
Explore lesson ChemistryLessonProcess Safety Principles in Chemical Plants
Industrial chemistry operates with large material inventories, high energy flows and equipment that can fail. A reaction that behaves calmly in a small flask may become difficult…
Explore lesson ChemistryLessonProduct Amount from the Limiting Reagent
Finding a limiting reagent is a decision point, not the final answer. The product calculation must use the reagent that limits reaction progress. A larger prediction from the…
Explore lesson ChemistryLessonProduct Mass and Gas Volume
An electrolytic cell converts charge into a chemical amount according to an electrode half-reaction. A scale can measure deposited metal, while a gas syringe can measure evolved…
Explore lesson ChemistryLessonProduct Selection in Aqueous Electrolysis
An aqueous electrolyte offers more than the ions named in its salt formula. Water is present in large amount and can be reduced to hydrogen or oxidized to oxygen. A realistic…
Explore lesson ChemistryLessonProducts of Neutralisation: Salt and Water
When an acid is neutralised by a base, the acidic and basic properties disappear, but the particles do not vanish. They rearrange into new substances. Every neutralisation…
Explore lesson ChemistryLessonProjection Operators
Sum-and-difference SALCs are easy to guess for two ligands, but phase patterns become difficult to invent for larger groups. Projection operators turn character-table information…
Explore lesson ChemistryLessonProof of the Variation Theorem
The variation principle is used so widely that it is worth seeing exactly why it is true. The proof is short and elegant. It relies on three facts established earlier in the…
Explore lesson ChemistryLessonPropagation and Termination
Once initiation has created radical chain ends, propagation consumes monomer and termination removes radicals. The balance between those events controls both the polymerisation…
Explore lesson ChemistryLessonPropagation of Measurement Uncertainty
Stoichiometric coefficients are exact within a chosen balanced equation, but masses, volumes and concentrations are measurements with uncertainty. A long calculation can look…
Explore lesson ChemistryLessonPropagation of Uncertainty
An analytical result often depends on several measured inputs: sample mass, flask volume, titrant concentration and delivered titre. Each has uncertainty. Propagation carries…
Explore lesson ChemistryLessonProperties of E and Z Isomers
E and Z isomers have the same atoms joined in the same order, yet they are genuinely different compounds with different physical constants. Because rotation about the double bond…
Explore lesson ChemistryLessonProperties of Simple Molecular Substances
Many substances made of small molecules melt or boil relatively easily and conduct electricity poorly. These patterns follow from the forces between their molecules and the…
Explore lesson ChemistryLessonProtecting Group Strategy
A useful reagent may attack or be quenched by a functional group that must remain intact in the final target. Temporarily masking that group can let the desired reaction proceed.…
Explore lesson ChemistryLessonProtecting Groups in Conversions
A molecule may contain two reactive groups when only one should change. A protecting group temporarily masks the interfering group, permits the desired reaction elsewhere, and is…
Explore lesson ChemistryLessonProtein Denaturation
Egg white becomes opaque when heated, and an enzyme can stop working after exposure to unsuitable pH. Such changes often involve protein denaturation: loss of a functional…
Explore lesson ChemistryLessonProtein Misfolding and Aggregation
The native fold is not the only possible organised state of a polypeptide. If part of a protein unfolds or is produced incorrectly, normally buried surfaces may become exposed.…
Explore lesson ChemistryLessonProtein Primary and Secondary Structure
A protein chain is more than a string of residue names. Its exact sequence is primary structure, while local backbone segments may form helices or sheets. These levels are…
Explore lesson ChemistryLessonProtein Tertiary and Quaternary Structure
Helices and sheets describe local protein shapes, but a working protein also needs an overall arrangement. Distant segments may pack together into a compact chain, and several…
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