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ChemistryClass 10CBSE

What is a precipitation reaction?

A precipitation reaction occurs when two soluble ionic solutions are mixed and an insoluble solid a precipitate forms.Example: AgNO₃(aq) + NaCl(aq) → AgCl(s)↓ + NaNO₃(aq)Precipitates are identified by colour: AgCl (white), PbS (black), BaSO₄ (white).Used in qualitative analysis to identify ions in solution.

ChemistryClass 10CBSE

What is a neutralisation reaction? Give an example.

A neutralisation reaction occurs when an acid and a base react to produce a salt and water.General Formula: Acid + Base → Salt + WaterAlways exothermic heat is released.Example: HCl + NaOH → NaCl + H₂OApplications: Antacids treat heartburn; lime treats acidic soil; baking soda treats insect stings.A neutralisation reaction between an acid

ChemistryClass 10CBSE

What is a chemical change? Give examples.

A chemical change produces new substances with properties entirely different from the originals, and is generally irreversible.Indicators:Change in colour, evolution of gas, formation of precipitate, temperature change, change in smell.Examples:Burning of wood → ash and smoke (irreversible)<li data-list-i

ChemistryClass 9CBSE

What are polyatomic ions? Give examples for Class 9.

A polyatomic ion is a group of two or more atoms covalently bonded together that carry an overall electric charge.Common Polyatomic Ions:Ion NameFormulaChargeAmmoniumNH₄⁺1+HydroxideOH⁻1−NitrateNO₃⁻1−SulphateSO₄²⁻2−Carbonate<t

ChemistryClass 10CBSE

What is molecular mass, and how is it calculated?

Molecular mass is the sum of the atomic masses of all atoms in one molecule of a substance, expressed in atomic mass units (u) or g/mol.Example: Water (H₂O):ElementNo. of AtomsAtomic MassTotalH212O11616Molecular Mass18 u&nb

ChemistryClass 10CBSE

What is atomic number?

The atomic number is the number of protons present in the nucleus of an atom.Symbol: ZUniquely identifies every element no two elements share the same atomic number.In a neutral atom, atomic number also equals the number of electrons.<li data-list-item-id="e6eb3735eea38d447f36b6730dba

ChemistryClass 10CBSE

What is the charge on a sulphide ion, S²⁻?

The charge on a sulphide ion is 2− (negative two).Sulphur (S) is in Group 16 and has 6 valence electrons.To achieve a stable octet, it gains 2 electrons, adding 2− charge: S²⁻.Examples:FeS: Fe²⁺ + S²⁻ → FeS<li data-list-item-id="e9d75261e2ac3fe13d

ChemistryClass 10CBSE

What is the valency of fluorine in calcium fluoride, CaF₂?

The valency of fluorine in CaF₂ is 1.Fluorine (F) belongs to Group 17 (halogens) and has 7 valence electrons.Needs 1 electron to complete its octet — forms one bond → valency of 1.In CaF₂: Calcium has valency 2, so bonds with two fluorine atoms (each valency 1).

ChemistryClass 10CBSE

Why does pure water always contain hydrogen and oxygen in a fixed ratio, regardless of its source?

Pure water always contains hydrogen and oxygen in the fixed ratio of 1:8 by mass (or 2:1 by number of atoms) because water is a compound, not a mixture.Elements in a compound are chemically bonded in a definite and fixed proportion this is the Law of Definite Proportions (Law of Constant Composition), stated by Joseph Proust.Every molecule o

ChemistryClass 10CBSE

What is the composition of misch metal?

Misch metal is an alloy of rare earth elements (lanthanides), primarily used in lighter flints and the steel industry.Composition:ComponentPercentageCerium (Ce)~50%Lanthanum (La)~25%Neodymium (Nd)~15%Other lanthanides + Iron~10%<li data-list-item-id="eff

ChemistryClass 10CBSE

What is an alloy? Give examples.

An alloy is a homogeneous mixture of two or more metals (or a metal and a non-metal) prepared to enhance desirable properties like strength, hardness, or corrosion resistance.Alloys are mixtures, not compounds their composition can vary.Made by melting metals together and cooling.Common Examples:<th

ChemistryClass 11CBSE

What are elements, compounds, and molecules?

These are three fundamental building blocks of matter, each more complex than the last.Element: A pure substance made of only one type of atom. Cannot be broken down further by chemical means. Examples: oxygen (O), iron (Fe), gold (Au).Compound: A pure substance formed when two or more elements combine chemically in a fixe

ChemistryClass 10CBSE

What is the mass of 10 moles of sodium sulphite, and how is it calculated?

The mass of 10 moles of sodium sulphite (Na₂SO₃) is 1260 g.Given:Formula: Na₂SO₃Number of moles = 10Molar Mass Calculation:ElementAtomsAtomic MassTotalNa22346S</

ChemistryClass 10CBSE

What is meant by a substance in chemistry?

A pure substance has a definite and uniform chemical composition and cannot be separated into simpler components by physical methods.Two types:Elements one kind of atom (e.g., gold, oxygen)Compounds two or more elements in fixed ratio (e.g., water, salt)Pure SubstanceMix

ChemistryClass 10CBSE

What is a chemical reaction?

A chemical reaction is a process in which one or more reactants are converted into one or more products through the breaking and forming of chemical bonds. No atoms are created or destroyed (Law of Conservation of Mass).Reactants → Products Example: 2H₂ + O₂ → 2H₂O (Hydrogen + Oxygen → Water) Types of chemical reactions:TypeDescriptionExample<

ChemistryClass 10CBSE

What is chemistry?

Chemistry is the branch of science that studies matter what it is made of, how its properties arise, how it changes, and how it interacts with other matter and energy.Core branches:BranchFocusOrganic chemistryCarbon-containing compounds; basis of life and pharmaceuticalsInorganic chemistryElements and compounds not primarily based on carbon

ChemistryClass 10CBSE

What is acid? Give an example of two locally available acidic substances.

An acid is a substance that donates hydrogen ions (H⁺) when dissolved in water, producing a solution with a pH below 7.Properties of acids:Sour taste (safe, dilute acids only)pH less than 7 (neutral water = pH 7)Turns blue litmus paper red<li data-list-item-id="eb0eebebe

ChemistryClass 11CBSE

2.8×10⁻³ mol of CO₂ is left after removing 10²¹ molecules from its ‘x’ mg sample. Find x. (Nₐ = 6.02×10²³ mol⁻¹)

Molar mass of CO₂ = 44 g/molStep 1 — Convert removed molecules to moles:Moles removed = 10²¹ / (6.02×10²³) = 1.661×10⁻³ molStep 2 — Initial moles = remaining + removed:n_initial = 2.8×10⁻³ + 1.661×10⁻³ = 4.461×10⁻³ molStep 3 — Initial mass:mass = 4.461×10⁻³ × 44 = 0.19629 g = 196.3 mgAnswer: x ≈ 196.3 mgDividing molecule count by Nₐ gives moles; multiplying by molar mass gives mass the two-step core of all JEE mole-conce

ChemistryClass 11CBSE

Total number of isomers, considering both structural and stereoisomers of cyclic ethers with the molecular formula C₄H₈O is

Degree of unsaturation = (2×4 + 2 − 8) / 2 = 1 → One ring, no double bonds.A cyclic ether contains one O atom inside the ring. Possible ring sizes: 3-membered (oxirane), 4-membered (oxetane), 5-membered (tetrahydrofuran).StructureIsomer Count2,2-dimethyloxirane1(R)-ethyloxirane1<

ChemistryClass 10CBSE

Why is NaOH's molar mass exactly 40?

Atomic masses: Na=23, O=16, H=1 → 23+16+1 = 40 g/mol exactly. This means 1 mole of NaOH weighs 40 g, making it easy to prepare 1M solutions (40 g per litre).

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