Chemistry explained: your questions answered

Question 1

How can I learn chemistry from zero?

Accepted Answer

Start with the foundations and keep them in order: atomic structure, the periodic table, valency and formulas, then the mole, equations and the classes of inorganic compounds. Learn each topic from your first school chemistry textbook, do three to five easy exercises right away, and mark whatever you don't understand. Chemistry builds in layers: you can't do calculations without the mole or balance redox equations without oxidation states.

Question 2

How do I learn to solve chemistry problems?

Accepted Answer

Most calculation problems follow one routine: write down the data with units, write and balance the equation, convert mass or volume to moles, use the mole ratio to find the moles of what you need, then convert back to grams or liters. Work through a solved example step by step first, then do several of the same type on your own. OrujovAI's Solve explains a chemistry problem step by step and gives you a similar one to practice.

Question 3

How do I prepare for DİM chemistry?

Accepted Answer

Chemistry is part of the second stage of the DİM admission exam, in subgroup RK of group I (weight 1) and in group IV (weight 1.5). In the model DİM uses in 2026, each subject has 30 tasks: 22 multiple-choice, 5 with coded answers and 3 written ones, and on the multiple-choice part four wrong answers cancel the points for one right answer. Build your prep around DİM's official syllabus, practice tests and calculation problems after each topic, and switch to timed full papers in the last months. Rules can change, so check the current exam model on dim.gov.az.

Question 4

How can I memorize the periodic table?

Accepted Answer

Don't try to learn the whole table at once: start with the first 20 elements in order, then the main groups, such as the alkali metals, halogens and noble gases. Understanding the trends matters more than rote memory: across a period metallic character decreases, and down a group it increases. Flashcards and a five-minute daily drill of filling in a blank table from memory work well.

Question 5

Can AI teach me chemistry?

Accepted Answer

Yes: AI can explain a topic at your level, work through examples, spot the mistake in your solution and quiz you. It works best as a tutor rather than an answer machine: ask it to question you first and explain afterwards, and write your own answers. It can still get things wrong, so check formulas and numbers against your textbook. OrujovAI's Live Tutor teaches a chemistry topic out loud as a lesson with a live board and quick checks along the way.

Question 6

How is the structure of the atom explained in chemistry?

Accepted Answer

An atom has a small positive nucleus made of protons and neutrons, with electrons around it. The number of protons equals the atomic number and defines the element; a neutral atom has the same number of electrons, and the number of neutrons is the mass number minus the atomic number. Chemical behavior depends mostly on the outer electrons, so learn to write electron arrangements by shells and orbitals (for sodium: 2, 8, 1 or 1s² 2s² 2p⁶ 3s¹).

Question 7

What does an element's place in the periodic table tell you?

Accepted Answer

The atomic number gives the number of protons and electrons, and the period number gives the number of electron shells. For main-group elements the group number matches the number of outer electrons and usually the highest oxidation state. From the position you can also predict whether an element is a metal or a non-metal, how its atomic radius and electronegativity compare with its neighbors, and which oxides and hydroxides it forms.

Question 8

What is valency?

Accepted Answer

Valency is the number of chemical bonds an atom forms with other atoms. In H₂O hydrogen has a valency of 1 and oxygen 2; in CH₄ carbon has a valency of 4. Some elements have a fixed valency (H, Na and K are 1; O, Mg and Ca are 2; Al is 3) while others vary (iron 2 or 3, sulfur 2, 4 or 6), so check the compound's name or the problem statement before writing a formula.

Question 9

How do I find an oxidation state?

Accepted Answer

The oxidation states of all atoms add up to zero in a neutral compound and to the ion's charge in an ion. Elements on their own are 0; in compounds hydrogen is usually +1, oxygen −2, alkali metals +1 and fluorine always −1. For H₂SO₄: 2 × (+1) + x + 4 × (−2) = 0, so sulfur is +6. Watch for exceptions such as peroxides, where oxygen is −1, and metal hydrides, where hydrogen is −1.

Question 10

What is a chemical bond?

Accepted Answer

A chemical bond is the attraction that holds atoms together in a molecule or crystal, and it is formed by the atoms' outer electrons. School courses cover four types: covalent, ionic, metallic (metal cations held together by electrons that move freely between them) and hydrogen bonds, which form between molecules. The type of bonding explains a lot about a substance, such as its melting point, hardness and whether it dissolves in water.

Question 11

What is the difference between covalent and ionic bonds?

Accepted Answer

In a covalent bond atoms share pairs of electrons, while in an ionic bond electrons move from one atom to another and the resulting ions attract each other. Covalent bonds usually form between non-metals (H₂, HCl, H₂O) and ionic bonds between a typical metal and a typical non-metal (NaCl, CaO). Covalent bonds can be non-polar, between identical atoms (Cl₂), or polar, between atoms with different electronegativity (HCl).

Question 12

What is a mole in chemistry?

Accepted Answer

A mole is the unit for amount of substance: 1 mol of anything contains 6.02 × 10²³ particles, whether atoms, molecules or ions. It lets chemists count particles far too small to see by weighing them instead. The amount is written n (or ν) and is found from mass as n = m / M, or for a gas at standard conditions as n = V / 22.4.

Question 13

How do I calculate molar mass?

Accepted Answer

Add up the relative atomic masses of all the atoms in the formula, taking the subscripts into account, and the result is the molar mass in g/mol. For H₂SO₄: 2 × 1 + 32 + 4 × 16 = 98 g/mol. Take atomic masses from the periodic table; school problems usually round them to whole numbers, except chlorine, which is taken as 35.5.

Question 14

What is Avogadro's number?

Accepted Answer

Avogadro's number is the number of particles in one mole: about 6.02 × 10²³ per mole. The number of particles is N = n × Nₐ, so 0.5 mol of oxygen gas contains 3.01 × 10²³ molecules. Read carefully when a question asks about atoms: each O₂ molecule has two atoms, so there are twice as many oxygen atoms as molecules.

Question 15

What is the molar volume of a gas?

Accepted Answer

It's the volume taken up by one mole of a gas. At the standard conditions used in Azerbaijani and Russian school problems (0 °C and 101.3 kPa) it's about 22.4 L/mol for any gas, so n = V / 22.4 and 11.2 L of CO₂ is 0.5 mol. The value applies only to gases and only under those conditions, so don't use it for liquid water or at other temperatures. Some international courses use 22.7 L/mol (0 °C and 100 kPa) or 24 L/mol at room temperature, so follow your own syllabus.

Question 16

How do I balance a chemical equation?

Accepted Answer

By the law of conservation of mass, each element must have the same number of atoms on both sides, and you fix this by placing coefficients in front of formulas. A handy order is metals first, then non-metals, then hydrogen, and oxygen last; never change the subscripts inside a formula. Example: 2H₂ + O₂ → 2H₂O. Finish by counting every element on both sides once more.

Question 17

What are the types of chemical reactions?

Accepted Answer

By what happens to the substances there are four basic types: combination (CaO + H₂O → Ca(OH)₂), decomposition (CaCO₃ → CaO + CO₂), single displacement (Zn + 2HCl → ZnCl₂ + H₂) and double displacement, or exchange (NaOH + HCl → NaCl + H₂O). Reactions are also classified as exothermic or endothermic, reversible or irreversible, catalyzed or uncatalyzed, and as redox reactions or reactions in which no oxidation state changes.

Question 18

What are acids?

Accepted Answer

Acids are compounds whose molecules contain hydrogen bonded to an acid residue, and in water they release H⁺ ions. Common examples are HCl, H₂SO₄, HNO₃ and H₃PO₄; acids can be oxygen-containing or oxygen-free, and monoprotic, diprotic or triprotic. They turn litmus red, neutralize bases and react with reactive metals to give hydrogen, although nitric acid usually doesn't release hydrogen with metals.

Question 19

What are bases?

Accepted Answer

In school chemistry, bases are compounds of a metal with one or more hydroxide (OH) groups, such as NaOH, Ca(OH)₂ and Fe(OH)₃. Bases that dissolve in water are called alkalis (NaOH, KOH, Ba(OH)₂); they release OH⁻ ions and turn phenolphthalein pink. Bases neutralize acids, and insoluble ones break down into an oxide and water when heated.

Question 20

How are salts formed?

Accepted Answer

Salts are made of metal cations (or NH₄⁺) and an acid residue, and there are many ways to get them: neutralizing an acid with a base, reacting a metal with an acid or a non-metal (2Na + Cl₂ → 2NaCl), a basic oxide with an acid, an acidic oxide with an alkali, or swapping ions between two salts. The classic case is NaOH + HCl → NaCl + H₂O. Salts can be normal (Na₂SO₄), acid salts (NaHSO₄) or basic salts (CuOHCl).

Question 21

How are oxides classified?

Accepted Answer

Oxides are binary compounds of an element with oxygen in the −2 state, and by behavior they are basic, acidic, amphoteric or neutral (non-salt-forming). Basic oxides come from typical metals (Na₂O, CaO), acidic oxides mostly from non-metals (CO₂, SO₃, P₂O₅), and amphoteric ones react with both acids and alkalis (ZnO, Al₂O₃). CO, NO and N₂O form no salts at all.

Question 22

How do I write ionic equations?

Accepted Answer

Write and balance the full equation first, then split strong electrolytes (soluble salts, strong acids and alkalis) into ions, keeping precipitates, gases, water and weak electrolytes as formulas. Cancel the spectator ions that appear unchanged on both sides, and what remains is the net ionic equation. For BaCl₂ + Na₂SO₄ it is Ba²⁺ + SO₄²⁻ → BaSO₄↓. Check what dissolves in a solubility table.

Question 23

What are redox reactions?

Accepted Answer

Redox reactions are reactions in which oxidation states change: one atom loses electrons (is oxidized) and another gains them (is reduced). The substance that gives away electrons is the reducing agent and the one that takes them is the oxidizing agent; in Zn + CuSO₄ → ZnSO₄ + Cu, zinc is the reducing agent and the copper ions are the oxidizing agent. Both processes always happen together, and the electrons lost equal the electrons gained.

Question 24

How do I balance a reaction with the electron balance method?

Accepted Answer

Assign oxidation states, find the elements that change, and write the oxidation and reduction steps separately with the number of electrons involved. Use the lowest common multiple of the electrons lost and gained to get the multipliers, put them in front of the reducing and oxidizing agents, then balance the remaining atoms, leaving hydrogen and oxygen until last. In 4NH₃ + 5O₂ → 4NO + 6H₂O, nitrogen loses 5 electrons (−3 to +2) and each O₂ molecule gains 4.

Question 25

What is a solution in chemistry?

Accepted Answer

A solution is a uniform (homogeneous) mixture of a solvent, most often water, and a dissolved substance, the solute. When salt or sugar dissolves, its particles spread out evenly, so the composition is the same throughout. Solutions can be unsaturated, saturated or supersaturated, and solubility depends on temperature and, for gases, on pressure too.

Question 26

How do I calculate mass fraction?

Accepted Answer

Mass fraction is the mass of the solute divided by the mass of the whole solution: w = m(solute) / m(solution) × 100%. The mass of the solution is solute plus solvent, so 20 g of salt in 80 g of water gives 100 g of solution at 20%. The most common mistake is dividing by the mass of the water instead of the solution.

Question 27

How do I find the concentration of a solution?

Accepted Answer

School chemistry mostly uses mass fraction (w, in %) and molar concentration (c = n / V, in mol/L). For molar concentration, convert the solute's mass to moles and divide by the solution's volume in liters: 4 g of NaOH (0.1 mol) in 0.5 L gives 0.2 mol/L. To go from mass fraction to molar concentration you need the density: c = 10 × w × ρ / M, with w in percent and ρ in g/mL.

Question 28

What affects the rate of a reaction?

Accepted Answer

Rate depends on the nature of the reactants, concentration, temperature, catalysts, surface area for solids and pressure for gases. By van 't Hoff's rule, every 10 °C rise usually makes a reaction 2 to 4 times faster. Problems give a temperature coefficient γ, and you find the change with v₂ = v₁ × γ^(Δt/10).

Question 29

What is chemical equilibrium?

Accepted Answer

Equilibrium is reached in a reversible reaction when the forward and reverse rates become equal: the reaction keeps going, but the concentrations stop changing. By Le Chatelier's principle the equilibrium shifts to counteract any change: removing product shifts it to the right, heating favors the endothermic direction, and raising pressure favors the side with fewer gas molecules. A catalyst doesn't shift equilibrium; it only helps the system get there faster.

Question 30

What is electrolysis?

Accepted Answer

Electrolysis is a redox process driven by passing an electric current through a molten or dissolved electrolyte. Reduction happens at the cathode (negative electrode) and oxidation at the anode (positive electrode): in molten NaCl, sodium forms at the cathode and chlorine at the anode. In aqueous solutions water takes part too, so for salts of very reactive metals hydrogen, not the metal, is released at the cathode.

Question 31

What is hydrolysis?

Accepted Answer

Salt hydrolysis is the reaction of a salt's ions with water, which can make the solution acidic or alkaline. A salt of a weak base and a strong acid (ZnCl₂, NH₄Cl) gives an acidic solution, a salt of a strong base and a weak acid (Na₂CO₃) gives an alkaline one, and a salt of a strong base and a strong acid (NaCl) doesn't hydrolyze, so the solution stays neutral. The rule of thumb: the stronger partner sets the medium.

Question 32

What is the reactivity series of metals?

Accepted Answer

It lists metals by how readily they act as reducing agents in water solutions: Li, K, Ba, Ca, Na, Mg, Al, Zn, Fe, Ni, Sn, Pb, (H), Cu, Hg, Ag, Pt, Au. Metals to the left of hydrogen displace it from acids (except nitric and concentrated sulfuric acid), and each metal displaces those to its right from solutions of their salts, as in Fe + CuSO₄ → FeSO₄ + Cu. Very reactive metals such as sodium react with the water itself first.

Question 33

What is organic chemistry?

Accepted Answer

Organic chemistry is the chemistry of carbon compounds: hydrocarbons, alcohols, carboxylic acids, carbohydrates, fats, proteins and polymers. Carbon forms four bonds and links into long chains and rings, which is why there are so many organic substances. A key idea in school courses is structural theory: a compound's properties depend not only on its formula but on the order in which its atoms are joined. Simple carbon compounds such as CO, CO₂ and carbonates are treated as inorganic.

Question 34

What are alkanes?

Accepted Answer

Alkanes are saturated hydrocarbons with the general formula CₙH₂ₙ₊₂, containing only single bonds. The series starts with methane CH₄, ethane C₂H₆, propane C₃H₈ and butane C₄H₁₀, and their names end in “-ane”. Typical reactions are substitution (such as chlorination in light) and combustion; they don't undergo addition because they have no double bonds, and methane is the main component of natural gas.

Question 35

What are alkenes?

Accepted Answer

Alkenes are unsaturated hydrocarbons with one C=C double bond and the general formula CₙH₂ₙ, such as ethene (ethylene) C₂H₄ and propene C₃H₆. The double bond lets them add hydrogen, halogens, water and hydrogen halides, and they polymerize: ethylene gives polyethylene. The standard test is that they decolorize bromine water and potassium permanganate solution.

Question 36

What are alkynes?

Accepted Answer

Alkynes are unsaturated hydrocarbons with one C≡C triple bond and the general formula CₙH₂ₙ₋₂; the simplest is ethyne (acetylene) C₂H₂. Like alkenes they undergo addition, but the triple bond fills up in two steps, first adding one molecule of hydrogen and then a second. Note that dienes share the formula CₙH₂ₙ₋₂, so they are isomers of alkynes.

Question 37

What are alcohols in chemistry?

Accepted Answer

Alcohols are organic compounds with one or more hydroxyl groups (–OH) attached to a saturated carbon atom. Saturated alcohols with one OH group have the general formula CₙH₂ₙ₊₁OH, for example methanol CH₃OH and ethanol C₂H₅OH, while glycerol has three OH groups. Alcohols release hydrogen with reactive metals, form esters with acids and burn; methanol is highly toxic.

Question 38

What are isomers?

Accepted Answer

Isomers are compounds with the same molecular formula but different structures, and therefore different properties. C₄H₁₀, for example, can be butane or isobutane (2-methylpropane). Structural isomers differ in the carbon chain or in the position of a multiple bond or functional group, while stereoisomers such as cis and trans forms differ in spatial arrangement; when counting isomers, make sure you don't draw the same molecule twice.

Question 39

How do I name organic compounds?

Accepted Answer

In IUPAC naming, pick the longest carbon chain and number it from the end nearest the multiple bond or functional group. Then give the positions and names of substituents (methyl, ethyl, chloro) and add the right ending to the parent chain: “-ane” for alkanes, “-ene” for alkenes, “-yne” for alkynes and “-ol” for alcohols. So CH₃–CH(CH₃)–CH₃ is 2-methylpropane and CH₂=CH–CH₂–CH₃ is but-1-ene.

Question 40

How are carbohydrates, fats and proteins studied in chemistry?

Accepted Answer

They come near the end of the school course as the chemistry of living things. Carbohydrates are split into monosaccharides (glucose, fructose), disaccharides (sucrose) and polysaccharides (starch, cellulose); fats are esters of glycerol and long-chain fatty acids, and proteins are polymers of amino acids joined by peptide bonds. You need the key reactions, such as hydrolysis, the silver mirror test for glucose and the blue-black color of starch with iodine, plus the biological role of each group.

Question 41

What are polymers?

Accepted Answer

Polymers are very large molecules built from many repeating units, and the small molecules they're made from are called monomers. In addition polymerization the monomers join with nothing given off (ethylene → polyethylene), while in condensation polymerization a small molecule such as water is released. Problems often ask for the degree of polymerization: divide the polymer's average molar mass by the molar mass of the repeating unit.

Question 42

How do I calculate the yield of a reaction?

Accepted Answer

Percentage yield is the actual mass (or volume) obtained divided by the theoretical amount calculated from the equation: yield = actual / theoretical × 100%. Work out the theoretical amount of product from the equation first, then divide the actual mass given in the problem by it. If the yield is given, multiply the theoretical mass by it to get the actual mass; a yield above 100% means there's a mistake somewhere.

Question 43

How do I solve excess and limiting reactant problems?

Accepted Answer

Find the moles of each reactant and divide each by its coefficient in the equation: the smaller result belongs to the limiting reactant, which is used up completely. Always calculate the product from the limiting reactant. With 2 mol H₂ and 2 mol O₂ (2H₂ + O₂ → 2H₂O), hydrogen is limiting, 2 mol of water forms and 1 mol of oxygen is left over.

Question 44

How do I solve gas volume problems?

Accepted Answer

At standard conditions, convert between volume and moles with n = V / 22.4, then use the coefficients of the equation. For reactions between gases there's a shortcut: by Gay-Lussac's law of combining volumes, gas volumes are in the same ratio as the coefficients, so 2 L of H₂ reacts with 1 L of O₂. At other conditions use the ideal gas equation pV = nRT.

Question 45

How do I solve mixing and dilution problems?

Accepted Answer

Most of them rest on one idea: when you mix, dilute or evaporate a solution, the mass of the solute doesn't change unless a reaction takes place. So find the solute mass in each solution (m = w × m(solution)), work out the mass of the new solution and take the ratio. When mixing two solutions, add up the solute masses and the solution masses separately.

Question 46

How do I write a chemical formula?

Accepted Answer

For a binary compound, find the valencies (or charges) of the two elements, take their lowest common multiple and divide it by each valency to get the subscripts. For aluminum (3) and oxygen (2) the LCM is 6, so 6 ÷ 3 = 2 and 6 ÷ 2 = 3, giving Al₂O₃. For salts, balance the charges of the cation and anion the same way: Ca²⁺ and PO₄³⁻ give Ca₃(PO₄)₂.

Question 47

Is there a website that balances chemical equations?

Accepted Answer

Yes: searching “chemical equation balancer” turns up free online tools that return the coefficients, and AI chatbots can also balance an equation and explain how they did it. They're good for checking your work, but you won't have them in an exam, so balance the equation yourself first and then compare. Solve on OrujovAI takes a typed equation and walks through the balancing step by step.

Question 48

Does AI balance chemical equations correctly?

Accepted Answer

Usually, especially for simple equations, but it can slip on complex redox reactions or when the products are written wrongly to begin with. The check is easy: count each element's atoms on both sides, and in ionic equations compare the total charge as well. Also check whether the reaction actually happens, using the solubility table and the reactivity series. In its standard mode, Solve on OrujovAI works the problem out a second time on its own and compares the two answers, though you should still do the last check yourself.

Question 49

Where can I find DİM-format chemistry tests?

Accepted Answer

The most reliable source is DİM itself: dim.gov.az publishes the tasks used in past exams with the correct answers, and DİM also issues test collections. Add practice exams from your school or a prep course. OrujovAI's Exam practice builds short DİM-format chemistry tests at three levels with an explanation for every question, though it doesn't include coded or written tasks yet.

Question 50

What are the safety rules in a chemistry lab?

Accepted Answer

Wear safety goggles and a lab coat, never taste chemicals or sniff them straight from the container (waft the smell toward you with your hand), and only do experiments your teacher has approved. When diluting concentrated acid, pour the acid slowly into the water, never the other way around, because water added to acid can boil and spatter. Point a heated test tube away from yourself and others, and if acid or alkali gets on your skin, rinse it with plenty of water at once and tell the teacher.

Question 51

How is chemistry connected to everyday life?

Accepted Answer

It shows up all around you: kettle scale is a carbonate deposit that vinegar or citric acid dissolves, antacid tablets work by neutralization, and rust is iron being oxidized. In Azerbaijan chemistry also means oil and gas: natural gas is mostly methane, and crude oil is turned into fuels and plastics. Asking yourself where each new topic shows up at home makes formulas much easier to remember.

Question 52

How do I prepare for a chemistry olympiad?

Accepted Answer

Olympiad chemistry goes well beyond the school syllabus, so finish the school course first, then move on to physical chemistry (thermodynamics, kinetics, equilibrium), analytical chemistry and deeper organic chemistry. Solve past olympiad problems: besides national rounds, the preparatory problems published each year for the International Chemistry Olympiad (IChO) are good practice. For the stages and rules in Azerbaijan, check the official website of the Ministry of Science and Education.

Question 53

What is electronegativity?

Accepted Answer

Electronegativity is an atom's ability to pull shared electrons toward itself in a bond. It increases across a period from left to right and decreases down a group; fluorine is the most electronegative element, followed by oxygen. The bigger the difference between two atoms, the more polar the bond, and with a very large difference the bond becomes ionic.

Question 54

What is a catalyst?

Accepted Answer

A catalyst speeds up a reaction but is left chemically unchanged, and in the same amount, at the end. It works by lowering the activation energy and doesn't shift the equilibrium. Manganese(IV) oxide, for example, speeds up the decomposition of hydrogen peroxide; in living things enzymes act as catalysts, and substances that slow reactions down are called inhibitors.

Question 55

What are exothermic and endothermic reactions?

Accepted Answer

Exothermic reactions release heat (combustion, neutralization), while endothermic reactions absorb it (most decompositions, such as heating CaCO₃). A thermochemical equation shows the heat effect, for example CH₄ + 2O₂ → CO₂ + 2H₂O + Q, and when it's written as an enthalpy change, ΔH is negative for an exothermic reaction. The heat is proportional to the amount of substance, so burning 2 mol of methane releases twice as much.

Question 56

Why do I keep losing points on chemistry problems?

Accepted Answer

The same few slips cause most lost points: an unbalanced equation, mixing up mass and moles or grams and kilograms, using 22.4 L/mol at non-standard conditions, taking the mass of the water instead of the solution, and calculating from the reactant in excess. After every problem, log your mistake by type in a notebook, and within a few weeks you'll see which ones keep coming back. You can also paste a solution you got wrong into OrujovAI's chat and ask it to find the step where it went off track.