Chemistry FAQ
Answers to common questions about learning chemistry, how the course is organised, and how to use the lessons, quizzes and tests.
Learning
Where should I start if I have never studied chemistry?
Begin at the Beginner level of Atomic Structure, then Bonding and States of Matter. Use the Roadmap on the home page; each step builds on the last.
How are the levels organised?
Beginner topics introduce core vocabulary and ideas. Intermediate topics add quantitative reasoning and mechanisms. Advanced topics cover theory, quantum models and research-level methods.
How should I use quizzes and tests together?
Use Quiz for practice with instant feedback and explanations. Use Test as a timed exam simulation with a full report at the end to find weak areas.
Is my progress saved?
Yes. Progress, bookmarks, quiz history and theme are stored in your browser only. Clearing site data or switching browsers resets them. You can reset manually on the Progress page.
How can I search?
Press / or Ctrl+K anywhere, or use the search box in the header. It searches topic names, descriptions, FAQ and elements, and tolerates small typos.
Concepts
What is the difference between an atom and a molecule?
An atom is a single unit of an element. A molecule is two or more atoms bonded together, for example O2 or H2O.
What is the difference between an element and a compound?
An element contains one type of atom. A compound contains two or more elements chemically bonded in fixed proportions.
What is a mole and why do we use it?
A mole is 6.022 x 10^23 particles. It links the invisible atomic scale to measurable grams, since one mole of a substance has a mass in grams equal to its molar mass.
Why does ice float on water?
Hydrogen bonding forces water molecules into an open hexagonal lattice in ice, making it about 9 percent less dense than liquid water.
Why are noble gases unreactive?
They have full valence shells, giving very high ionization energies and almost no tendency to gain or share electrons. Heavier ones like xenon can still form compounds with fluorine and oxygen.
What is the difference between ionic and covalent bonds?
Ionic bonds transfer electrons and form between metals and nonmetals. Covalent bonds share electrons, usually between nonmetals. Most real bonds fall between the two extremes.
Why is the periodic table shaped this way?
Rows are periods where valence shells fill, columns are groups with the same valence electron count. The blocks (s, p, d, f) follow the subshell being filled.
Problem Solving
How do I balance a chemical equation?
Write correct formulas, count atoms of each element on both sides, and adjust coefficients only (never subscripts). Balance elements appearing in one compound first, and leave H and O for last.
How do I find the limiting reagent?
Convert each reactant to moles, divide by its coefficient, and compare. The smallest value belongs to the limiting reagent.
How do I calculate pH?
pH equals minus log10 of the hydrogen ion concentration. For strong acids use the acid concentration; for weak acids solve with Ka and an ICE table.
What is the easiest way to remember oxidation and reduction?
OIL RIG: Oxidation Is Loss of electrons, Reduction Is Gain.
How do I decide whether a reaction is spontaneous?
Calculate delta G equal to delta H minus T times delta S. If delta G is negative the reaction is spontaneous under those conditions.
How do I draw a Lewis structure?
Count total valence electrons, connect atoms with single bonds, complete octets on outer atoms, put leftovers on the central atom, and form multiple bonds if the central atom lacks an octet.
How do I predict molecular shape?
Count electron groups around the central atom (bonds and lone pairs), choose the electron geometry using VSEPR, then name the shape from the bonded atoms only.
Practical
Why must I wear goggles in the lab?
Splashes can permanently damage eyes within seconds. Goggles are mandatory whenever chemicals, glassware or heating are involved.
What does significant figures mean in measurements?
They are the meaningful digits of a measured value, including one estimated digit. Results should not be reported more precisely than the least precise measurement.
What is the difference between accuracy and precision?
Accuracy is how close to the true value. Precision is how close repeated measurements are to each other.
How do I dilute an acid safely?
Always add acid slowly to water, never water to acid, because the heat released can make concentrated acid spatter.
Advanced
Why do quantum numbers matter in chemistry?
They define each electron's energy, orbital shape, orientation and spin, and explain the structure of the periodic table and spectra.
Why do transition metals have colourful compounds?
Ligands split the d orbitals into groups of different energy. Electrons absorb visible photons matching the gap and the transmitted complement is the colour seen.
What is the difference between SN1 and SN2?
SN2 is one-step with backside attack and inversion, favoured by primary substrates and strong nucleophiles. SN1 goes through a carbocation, favoured by tertiary substrates and polar protic solvents, giving racemization.
What does a catalyst do to equilibrium?
Nothing to the position. It lowers activation energy for both directions equally so equilibrium is reached faster.
What is green chemistry?
A design philosophy that reduces hazardous substances and waste, uses renewable feedstocks and maximizes atom economy.
About
How many topics does this app contain?
Over 1,100 topics across 10 areas, plus 118 elements, interactive labs, quizzes, mock tests and flashcards.
Does the app work offline?
Yes, once loaded all content is inside the app files. No network connection is needed except for the first page load.
Can I use this for exam preparation?
It is excellent for revision and self-testing, but always align with your own syllabus and textbooks, as curricula differ between regions.