Chemistry questions and answers
Elements, compounds, reactions, periodic table, acids, bases and bonds.
These are practice variations, many generated from templates and numeric inputs, not an official question bank. They remain outside search indexing until at least 100 independently reviewed questions across five chapters are available.
Questions and clear answers
01Atoms · foundation · Editorial previewWhat is the atomic number?+
An element's atomic number equals the number of protons in the nuclei of its atoms.
02Matter · foundation · Editorial previewWhat is the difference between a mixture and compound?+
A mixture combines substances without a fixed chemical ratio; a compound has chemically bonded elements in a fixed ratio.
03Reactions · foundation · Editorial previewWhat is oxidation in terms of electrons?+
Oxidation is the loss of electrons and occurs alongside a corresponding reduction reaction.
04Acids and bases · foundation · Editorial previewWhat does pH indicate?+
pH is related to hydrogen-ion activity and is used to describe how acidic or basic an aqueous solution is.
05Moles · advanced · Editorial previewIn chemistry — Moles: Each of 8 identical containers holds 90 g of water. Using molar mass 18 g/mol, how many moles are there across all containers?+
Total mass = 8 × 90 g; moles = total mass/18 = 40 mol.
06Mass and atoms · foundation · Editorial previewIn chemistry — Mass and atoms: There are 15 containers holding 12 mol of particles each. Using Nₐ = 6.022 × 10²³/mol, how many particles in all?+
Total mol = 15 × 12 = 180; entities ≈ 1083.96 × 10²³.
07Solutions · foundation · Editorial previewIn chemistry — Solutions: Dissolve 19 mol of solute and make up 5 litres of solution. Find molarity.+
Molarity = moles/volume = 19/5 ≈ 3.8 mol/L.
08Concentration · intermediate · Editorial previewIn chemistry — Concentration: A sample has 960 units, of which 956 meet the stated condition. What percentage meet it, rounded to two decimals?+
99.58% because 956 ÷ 960 × 100 = 99.58%.
09pH · foundation · Editorial previewIn chemistry — pH: A formal model solution has [H⁺] = 10^(-10) mol/L and volume 2 L. Under an ideal concentration model, find pH and moles of hydrogen ions.+
pH = 10; amount of H⁺ = 2 × 10^(-10) mol. This is a formal model; real dilute solutions require activity/water considerations.
10Stoichiometry · advanced · Editorial previewIn chemistry — Stoichiometry: In 9 vessels, each contains 34 mol H₂ and sufficient O₂ for 2H₂ + O₂ → 2H₂O. What total moles of H₂O could form?+
Each vessel makes 34 mol H₂O from 34 mol H₂; total = 9 × 34 = 306 mol H₂O.
11Gas particles · intermediate · Editorial previewIn chemistry — Gas particles: A model sample holds 2789 packets of 24 particles each. How many particles are represented?+
Multiply packets by particles per packet: 2789 × 24 = 66936 particles.
12Density of liquids · foundation · Editorial previewIn chemistry — Density of liquids: A sample has mass 27200 g and volume 8 cm³. Find density.+
Density = mass/volume = 27200/8 = 3400 g/cm³.
13Mass conservation · foundation · Editorial previewIn chemistry — Mass conservation: In a closed reaction, 4011 g of one reactant combines completely with 46 g of another. Find the total product mass.+
Conservation of mass: 4011 + 46 = 4057 g (assuming all matter is accounted for).
14Empirical formula · intermediate · Editorial previewIn chemistry — Empirical formula: A compound contains 22 atoms of element X and 3 atoms of Y per molecule. Write its symbolic model formula.+
The model is X22Y3 (a symbolic exercise, not a claim that this is an actual stable compound).
15Periodic properties · advanced · Editorial previewIn chemistry — Periodic properties: A neutral hypothetical atom has 234 protons. How many electrons does it contain?+
Electrical neutrality means electrons equal protons, so it has 234 electrons. This does not identify a real stable isotope.
16Dilution · foundation · Editorial previewIn chemistry — Dilution: A stock solution is 13 mol/L. What volume of stock is needed to prepare 17 L at 6.5 mol/L?+
Using C₁V₁=C₂V₂: V₁ = (6.5 × 17)/13 ≈ 8.5 L (rounded concentrations).
17Moles · intermediate · Editorial previewIn chemistry — Moles: Each of 7 identical containers holds 360 g of water. Using molar mass 18 g/mol, how many moles are there across all containers?+
Total mass = 7 × 360 g; moles = total mass/18 = 140 mol.
18Mass and atoms · foundation · Editorial previewIn chemistry — Mass and atoms: There are 14 containers holding 4 mol of particles each. Using Nₐ = 6.022 × 10²³/mol, how many particles in all?+
Total mol = 14 × 4 = 56; entities ≈ 337.232 × 10²³.
This is an educational practice preview. Answers and board-specific alignment are undergoing editorial review; these are not official exam questions.