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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 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 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 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).

ChemistryClass 10CBSE

Molecular Mass Calculations

NaOH molecular mass = 40 g/mol:Na(23) + O(16) + H(1) = 40 g/mol FeSO₄·7H₂O (Green Vitriol) = 278 g/mol:Fe(56) + S(32) + 4×O(16) + 7×H₂O(18) = 56 + 32 + 64 + 126 = 278 g/mol Na₂SO₄·10H₂O (Washing Soda / Glauber's Salt) = 322 g/mol:2×Na(23) + S(32) + 4×O(16) + 10

ChemistryClass 10CBSE

Synthetic Indicators&nbsp;

IndicatorTypeIn AcidIn BaseLitmusNaturalRedBlueTurmericNaturalYellowRed-brownPhenolphthaleinSyntheticColourlessPinkMethyl OrangeSyntheticRedYellow</

ChemistryClass 10CBSE

Why polar aprotic → SN2

No H-bonding with nucleophile → nucleophile stays "naked" and

ChemistryClass 10CBSE

Polar Aprotic Solvents

FeatureProtic SolventsPolar Aprotic SolventsO–H / N–H bondsYesNoH-bond donationYesNoExamplesWater, ethanolDMSO, DMF, acetoneFavoursSN1 reactionsSN2 reactions

ChemistryClass 10CBSE

Conditions for ionic bond formation

Large electronegativity difference (>1.7 Pauling units)Low ionisation energy of the metal (easy electron loss)High electron affinity of the non-metal (eager electron gain)High lattice energy of the product (stabilises the ionic crystal)<li d

ChemistryClass 10CBSE

Salt and diabetes

Excess salt is NOT recommended it raises blood pressure, worsening diabetic kidney and heart complications. WHO recommends <5 g/day; diabetic patients should follow a low-sodium diet.

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