81 interactive simulators

Ten unknown samples are given, named “Sample A … Sample J”, and you analyze them with four reagents: flame color, sodium hydroxide, barium chloride and silver nitrate. After a precipitate forms, you add excess NaOH/NH₃, dilute HCl or ammonia solution for the final identification, and the ionic equation for each reaction appears right away. It follows the textbook flowcharts in Figure 1.4.2 (cations) and 1.4.3 (anions) exactly, and once you identify all the samples, it shows your score and number of mistakes.

On the left, filter by reaction type (substitution, addition, elimination, esterification, hydrolysis, oxidation, polymerization, isomerization, nitrogen compounds) and choose a reaction. In the center, the mechanism plays frame by frame: starting material and reagent → bond breaking, new bond formation, carbocation or enol intermediate → product. Step through it manually with the ◀ ▶ buttons, or automatically with ▶▶ (every 0.9 s). In reactions that follow Markovnikov’s rule, the reminder “hydrogen adds to the carbon that already has more hydrogens” appears, and secondary and primary carbocations are shown side by side. On the right: the full equation with its conditions, an explanation of the step and a “Why?” note. In “Test” mode you get 10 questions: predict the product, name the reaction type, choose the major Markovnikov product and identify the conditions.

How are strong and weak acids different? Use your lab tools to find out! Dip pH paper or the meter into the solution to measure the pH, or test the conductivity with the electrodes. Then watch how the type and strength of the solution affect the pH. Can a weak acid solution have the same pH as a strong acid solution?

What happens when two atoms get close? Atoms weakly attract each other from far away, but strongly repel if they get too close. Choose a pair of atoms (neon, argon, oxygen), change the distance between them and watch how the potential energy curve (σ and ε) changes. The movable atom oscillates around its equilibrium point — just as if the two were joined by an invisible spring!

In a chemical reaction, atoms are neither created nor destroyed — they are only rearranged. So the number of atoms of each element must be equal on both sides of the equation. Adjust the coefficients (the numbers) up and down to balance the equation. You can check it with molecules, a balance scale or a bar chart. When it balances, 😊 appears!

What happens when you rub a balloon on a sweater? Negative charges (electrons) move from the sweater to the balloon, and the balloon becomes negatively charged. The negatively charged balloon attracts the wall and sticks to it (static electricity). Drag the balloon, rub it on the sweater, then take it to the wall. Tap “Remove wall” and the balloon goes back to the positively charged sweater. Watch what’s happening in the show-charges mode!

What is the concentration of a solution? Concentration = moles of solute / volume of solution. Add substance to the beaker and the concentration rises; add water (dilute) and it drops. Evaporate water and the concentration rises again, but pouring out solution leaves the concentration unchanged. Choose substances of different colors, dip the concentration meter into the solution and measure in mol/L. Add too much substance and the solution becomes saturated, and the excess settles to the bottom!

Coffee, milk, soda, battery acid — how acidic or basic are these liquids? The pH scale runs from 0-14: 7 is neutral (water), below 7 is acidic, and above it is basic. Choose a liquid, dip the pH meter into the solution and measure. Watch how adding water (diluting) brings the pH closer to 7 (neutral)!

Molarity (mol/L) = moles of solute / volume of solution (in liters). Use the sliders to change the amount of solute (mol) and the volume of solution, and watch how the concentration changes. The more solute or the smaller the volume, the higher the concentration. If it gets too high, the solution becomes saturated and the excess settles to the bottom!

An atom is made of protons, neutrons and electrons. Protons and neutrons are in the nucleus, and electrons are in the shells. The number of protons determines the element (1 proton = hydrogen, 2 = helium...). Change the numbers of protons, neutrons and electrons and watch: which element you get, and how the charge (protons − electrons) and the mass number (protons + neutrons) change. If protons and electrons are equal, it’s a neutral atom; if not, it’s an ion!

Molecules are made of atoms. Combine hydrogen (H), oxygen (O), carbon (C) and nitrogen (N) atoms in the right ratios to build molecules. Example: 2 hydrogen + 1 oxygen = water (H₂O). As soon as the right atoms join, the molecule forms automatically and is added to your collection. How many molecules can you build?

Atoms of the same element can have different numbers of neutrons — these are called isotopes. Isotopes have the same number of protons (so they’re the same element) but different mass numbers (protons + neutrons). Choose an element and change the number of neutrons, then watch: which isotope you get, how abundant it is in nature, and its atomic mass. Example: carbon-12 is the most abundant, while carbon-14 is unstable!

During a reaction, the reactants are used up in a fixed ratio. If one reactant runs short (the limiting reactant), some of the other is left over. Example: 2 slices of bread + 1 slice of cheese = 1 sandwich. If you have 5 slices of bread and 3 slices of cheese, how many sandwiches can you make, and what is left over? Adjust the amounts of reactants and watch how the products and leftovers change. Try it with real reactions too, like making water and ammonia!

Why are solutions colored? Shine a laser into a colored solution and use the detector to measure how much light is absorbed and how much passes through. Change the solute, the concentration, the cuvette width and the wavelength of the light, and watch how absorbance changes according to Beer’s law A = ε·l·c. The more concentrated the solution and the wider the cuvette, the more light is absorbed.

Atoms don’t attract electrons equally strongly. Change the electronegativity (EN) of the two atoms and watch the electrons shift toward the atom that pulls harder, making it δ− (negative) and the other δ+ (positive). The bond dipole arrow shows the EN difference: a small difference means a covalent bond, a large one an ionic bond. Turn on the electric field and the polar molecule turns to line up with the field.

Why does wood float in water while iron sinks? Density = mass ÷ volume. Choose a material (wood, ice, glass, iron, copper, gold) and change its volume, or make your own block and set its mass and volume. If its density is less than the density of water, 1.0 kg/L, the block floats; if greater, it sinks. When a block floats, how much of it sits underwater depends on its density.

Why does a smell spread through a room? The container is split into two parts by a wall: blue gas particles on the left, red ones on the right. Set the number of particles and the temperature, then tap the “Remove wall” button. The particles keep moving and colliding, gradually mixing until they spread evenly throughout the container. The higher the temperature, the faster the particles move and the faster they spread.

How do charges affect each other? Coulomb’s law: F = k·q₁·q₂ / r². Drag the two charges along the line to change the distance, and set their size and sign (+/−). Like charges repel, and opposite charges attract. The bigger the charges and the closer they are, the more sharply the force increases.

What is an atomic nucleus made of? Add and remove protons and neutrons to build a nucleus. The number of protons determines which element it is, and protons+neutrons give the mass number. See on the nuclide chart whether the nucleus is stable (dark blue) or decays radioactively (β⁻, β⁺, emission). If there are too many or too few neutrons, the nucleus becomes unstable.

How does light interact with molecules? Choose a light source (microwave, infrared, visible light, ultraviolet) and shoot photons at a molecule. The molecule absorbs a photon with the right energy and responds: water rotates, carbon dioxide vibrates, nitrogen dioxide glows, and ozone breaks apart in ultraviolet light. Some molecules, such as N₂ and O₂, let the light pass straight through.

How did Rutherford discover the atomic nucleus? Fire positively charged alpha particles at a thin gold foil. Most pass straight through, but some that pass near a nucleus are sharply deflected by Coulomb repulsion, and those that hit it head-on bounce back. Change the number of protons in the nucleus or the energy and watch how the deflection changes — this experiment proved that an atom’s mass is concentrated in a tiny nucleus.

Why do molecules have particular shapes? Add bonds (single, double, triple) and lone pairs of electrons to the central atom. Electron pairs repel each other and spread out as far apart as possible (VSEPR theory). Depending on the number of domains, you get shapes such as linear, trigonal planar, tetrahedral, bent and pyramidal. Adding a lone pair changes the shape and makes the bond angle smaller.

Why does ice melt and water evaporate? Choose a substance (neon, argon, oxygen, water) and change the temperature with the heater/cooler. When cold, the particles form a lattice and barely move (solid); when warm, they separate and flow (liquid); when hot, they fly around freely (gas). Watch the temperature and phase on the thermometer.

What does gas pressure depend on? Add particles with the pump, change the temperature with the heater/cooler, and move the piston to reduce the volume. The particles bounce elastically off the walls and create pressure. The more particles, the hotter the gas or the smaller the volume, the higher the pressure (PV = NkT). Watch the pressure on the gauge and the temperature on the thermometer.

How are a gas’s pressure, volume and temperature related? Add heavy (blue) and light (red) particles with the pump. Choose “Constant T” and the pressure rises when you reduce the volume (Boyle’s law, P·V=const). Choose “Constant V” and the pressure rises when you heat it (Gay-Lussac’s law, P/T=const). Watch the relationship curve on the mini-graph.

Why do molecules have particular shapes? Add single bonds and lone pairs of electrons to the central atom. Electron domains repel each other and spread out as far apart as possible (VSEPR theory): 2 domains give a linear shape, 3 trigonal planar and 4 tetrahedral. Adding a lone pair changes the shape (water is bent, ammonia is pyramidal) and makes the bond angle smaller. Try it with CO₂, BF₃, H₂O, NH₃ and CH₄.

Coffee, milk, lemon, soap — how acidic or basic are they? When you choose a liquid, the pH meter shows a value from 0–14: 7 is neutral, lower is acidic (red), higher is basic (pink). Show the ratio of H₃O⁺ (acid) and OH⁻ (base) ions as bars. In acidic liquids H₃O⁺ dominates, while basic ones have lots of OH⁻.

Why do substances change between the solid, liquid and gas states? Choose neon, argon, oxygen or water and change the temperature with the heater/cooler. When cold, the particles form a lattice and barely move (solid); when warm, they separate and flow (liquid); when hot, they fly around freely (gas). A dot shows where the substance sits on the phase diagram depending on temperature and pressure — more detailed than the Basics version!

Choose an element with Z=1..20 and the energy diagram shows how electrons fill the orbitals by the Aufbau principle — starting from the lowest-energy orbital — and how, by Hund’s rule, they first occupy orbitals of equal energy one at a time. The full (1s²2s²…) and shorthand ([Ne]3s¹) notations of the electron configuration appear side by side.

Tap any of the first 20 elements in the periodic table to draw the Bohr model of its atom. Move right and down, compare, and see for yourself that period = number of shells and group = number of electrons in the outer (valence) shell.

Shows the atomic radius, ionization energy, electronegativity and metallic character of the first 20 elements as a color map (heatmap). Choose a trend and tap elements to compare their values — the pattern of how they change across a period and down a group is visible at a glance.

Choose a cation (positive ion) and an anion (negative ion), and the subscripts are worked out by the criss-cross rule to build the compound’s formula: Al³⁺ + O²⁻ → Al₂O₃. The compound’s name, class (oxide, base, acid, salt) and charge balance are shown alongside — master formula writing right here!

Metals, nonmetals, acids, bases, oxides, salts — mix any of the 60 substances however you like. If a reaction happens, you’ll see the color in the flask change, bubbles form, a precipitate settle, and heat released or absorbed. Best of all, every reaction is written in three forms at once: a word equation, chemical formulas and the balanced equation. With the “Heat 🔥” button you can also see a single substance decompose.

A real lab bench: add water, acids, bases, salts, metals and indicators to a glass beaker and watch what happens. The table instantly shows each substance’s moles, solubility (g/L) and what percent of it has dissolved. Raising the temperature changes the solubility. Every reaction that takes place is recorded with its word equation and balanced equation. In “Burner” mode, put a substance on a watch glass, heat it in the flame and see the decomposition reaction.

Choose a reaction from five types — combination, combustion, single displacement, double displacement and decomposition — and adjust the coefficients with the +/− buttons. The table shows the number of atoms of each element on the left and right sides and turns green when they balance. If you get stuck, the “Answer” button shows the correct coefficients.

The activity series of metals (K…Au, with H₂ marked) and the halogen series (F₂ > Cl₂ > Br₂ > I₂) are always on screen. Choose an element and put it into an acid, water or a salt solution — you’ll instantly see whether a reaction happens, why, and the balanced equation.

Choose from 20 compounds made of 3–4 elements, such as H₂SO₄, KMnO₄ and K₂Cr₂O₇, and use the known oxidation states (H +1, O −2 …) to find the oxidation state of the marked element with the +/− buttons. If you’re right, the full worked solution appears.

20 redox reactions at 3 levels: easy, medium and advanced. For each reaction you see the oxidized and reduced elements, the number of electrons transferred and the reaction type (intermolecular, intramolecular, disproportionation), and you balance it with the atom-count table.

There are 12 kinds of trash floating in the lake. Sort them correctly into the plastic, glass, metal and organic bins, and the pollution level drops, the water gradually turns clear and the fish and other animals come back.

Shows the cycle in which factory smoke — SO₂ and NO₂ gases — gets into the clouds and turns into acid rain. Remove the sources one by one and the rain’s pH rises from 3.5 to 5.6, the pH of clean rain, and the withered plants bloom again.

Remove sources such as raw coal, old buses and unfiltered chimneys, and put improved fuel, electric transport and filters in their place. The AQI drops from 300 to 50 and the smoggy sky clears.

In a landscape of mountains, a river and forest, there are polluters such as sewage, garbage dumps and smoking chimneys. Remove them, then add treatment plants and sorting bins and plant trees — the river turns clear and the animals come back.

Turn the burette’s stopcock to pour into the beaker drop by drop or in a stream. Choose substances from the categories water, acids, bases, salts, indicators and organics, and see the moles and percent dissolved in the contents table. Raising the temperature changes the solubility, and above 100°C it boils. The reactions tab shows the reactions in the beaker as balanced equations.

Drip ethanol onto a metal dish and light it to get a blue flame. Add a metal salt and the flame turns the color of that ion: potassium violet, sodium yellow, copper blue-green, calcium orange. In test mode, guess which ion a hidden salt contains from its flame color — a real analytical chemistry method.

Mix solutions of 8 cations (Ag⁺, Pb²⁺, Ba²⁺, Ca²⁺, Cu²⁺, Fe²⁺, Fe³⁺, Na⁺) and 7 anions (Cl⁻, I⁻, SO₄²⁻, CO₃²⁻, OH⁻, S²⁻, NO₃⁻) in pairs and instantly see from the solubility rules whether a precipitate forms. If one does, the beaker turns cloudy and a colored pile settles at the bottom, and both the complete and net ionic equations are written. Then use the “Filter” button to leave the precipitate on the paper and let the filtrate drain through, as in Figure 1.3.3, and use “Dry” to obtain the pure salt — how many of the 26 precipitates can you find?

Choose one of 8 substances (pure water, naphthalene, stearic acid, pure copper — salt water, ice with soil, candle wax, bronze alloy) and tap “Heat”: the clock starts and the temperature–time curve is drawn realistically from left to right in ~4 seconds. When a pure substance reaches its melting point, the curve goes FLAT — all the heat is used to break down the crystal structure; a mixture has no flat section, only a SLOPED range, and this is shown with bold markers, dashed lines and explanations. The “Compare” button plots two substances on the same axes at once (for example, pure water and salt water, or pure copper and bronze alloy) so you can compare the difference right away.

Choose a substance from the list on the left, put a spot on the pencil start line and dip the paper into the solvent in the glass jar. As the solvent soaks up the paper, a spot that looked like one separates and moves up, and when the solvent front stops, each spot’s Rf value (distance traveled by the spot a ÷ distance traveled by the solvent b) is measured with arrows and dashed lines. One spot means PURE; two or more spots mean a MIXTURE — test all 10 substances (4 pure, 6 mixtures) to get the overall conclusion.

Choose a process on the left and step through each stage with the ◀ ▶ buttons — every piece of equipment, such as the roasting furnace, converter, absorption tower, blast furnace, flotation tank and Frasch well, appears as an animated diagram with its pipes, flows, flames and thermometers. On the right, the conditions for that stage (temperature, pressure, catalyst) are shown in bold above its equation, and the explanation uses the textbook’s wording. In “Adjust” mode, change the temperature, pressure and catalyst for the Contact process and the Haber process — the product yield and reaction rate change instantly and are compared with the optimal industrial conditions. In “Test” mode you get 6 questions: put the stages in order, choose the conditions and identify the reactions.

View the catalog’s 140 organic compounds in three representations (expanded, condensed and skeletal), along with their IUPAC name, general formula, properties, a boiling-point chart for the homologous series, and isomers. In “Build” mode, choose the chain, multiple bonds, functional groups and substituents to assemble a molecule and get its name. In “Test” mode there’s a set of 10 questions.