CBSE · Class 10 · All chapters

Chemistry — Complete Formula Sheet

Board Formulas

50 formulas · 6 chapters

Ch 1 · Chemical Reactions and Equations

1.General Combination Reaction★
$A + B ⟶ A B$
Two or more reactants combine to form a single product. Often exothermic. Example: CaO + H₂O → Ca(OH)₂.
2.General Decomposition Reaction★
$A B ⟶ A + B$
A single reactant breaks into two or more products. Requires heat / light / electricity. Endothermic.
3.Thermal Decomposition of Calcium Carbonate
$C a C O_{3} (s) Δ C a O (s) + C O_{2} (g)$
Basis of lime industry. Products: quicklime (CaO) and carbon dioxide.
4.Displacement Reaction
$A + B C ⟶ A C + B$
More reactive element A displaces less reactive B. Example: Fe + CuSO₄ → FeSO₄ + Cu (blue → green).
5.Double-Displacement (Precipitation)★
$A B + C D ⟶ A D + C B$
Ions swap partners; often produces an insoluble precipitate. Example: Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2 NaCl.
6.Photochemical Decomposition of AgCl
$2 A g C l (s) h ν 2 A g (s) + C l_{2} (g)$
White silver chloride turns grey in sunlight — basis of black-and-white photography.
7.Oxidation and Reduction (Redox)
$oxidation loss of e^{-} ∣∣ reduction gain of e^{-}$
Redox = oxidation + reduction happen together. Mnemonic: OIL RIG — Oxidation Is Loss, Reduction Is Gain (of electrons).
8.Formation of Rust
$4 F e (s) + 3 O_{2} (g) + 2 x H_{2} O ⟶ 2 F e_{2} O_{3} \cdot x H_{2} O (s)$
Rust needs BOTH oxygen and water. Prevention: painting, galvanising, alloying (stainless steel).

Ch 2 · Acids, Bases and Salts

1.Acid Ionisation in Water★
$H C l (a q) + H_{2} O (l) ⟶ H_{3} O^{+} (a q) + C l^{-} (a q)$
Acids produce H⁺ (or hydronium H₃O⁺) in water. The H⁺ ion is responsible for acidic behaviour.
2.Base Ionisation in Water
$N a O H (a q) ⟶ N a^{+} (a q) + O H^{-} (a q)$
Bases produce OH⁻ ions in water. Only water-soluble bases are called alkalis.
3.Neutralisation★
$A c i d + B a se ⟶ S a l t + W a t er$
H⁺ from acid combines with OH⁻ from base. Highly exothermic.
4.Acid + Metal
$A c i d + M e t a l ⟶ S a l t + H_{2} (g)$
Common active metals (Zn, Fe, Mg) liberate H₂ gas with dilute acids. Test: hydrogen 'pops' with a burning splinter.
5.Acid + Metal Carbonate
$2 H C l + N a_{2} C O_{3} ⟶ 2 N a C l + H_{2} O + C O_{2} (g)$
Bubbles of CO₂ turn lime water milky (Ca(OH)₂ + CO₂ → CaCO₃↓). Same result with metal hydrogencarbonates.
6.pH Scale★
$p H = - lo g_{10} [H^{+}]$
$[H^{+}]$ : Molar concentration of H⁺ ions (mol/L)
Range 0-14. pH < 7 acidic, pH = 7 neutral, pH > 7 basic. Each unit change ⇒ 10× change in [H⁺].
7.Chlor-Alkali Process
$2 N a C l (a q) + 2 H_{2} O (l) electrolysis 2 N a O H (a q) + C l_{2} (g) + H_{2} (g)$
Industrial electrolysis of brine. Products: NaOH at cathode, Cl₂ at anode, H₂ as by-product.
8.Water of Crystallisation
$C u S O_{4} \cdot 5 H_{2} O Δ C u S O_{4} + 5 H_{2} O$
Fixed number of water molecules in the crystal lattice. Blue (hydrated) → white (anhydrous). Adding water reverses it.
9.Setting of Plaster of Paris
$C a S O_{4} \cdot \frac{1}{2} H_{2} O + \frac{3}{2} H_{2} O ⟶ C a S O_{4} \cdot 2 H_{2} O$
PoP + water → gypsum. Slight expansion on setting makes it ideal for casts/moulds.

Ch 3 · Metals and Non-Metals

1.Ionic Bond Formation★
$N a ⟶ N a^{+} + e^{-}; C l + e^{-} ⟶ C l^{-}$
Metal loses electron(s) to attain noble-gas configuration; non-metal gains. Attraction between the two ions is the ionic bond.
2.Metal + Oxygen
$2 M + O_{2} ⟶ 2 M O$
Metal oxides are usually BASIC. Some (Al₂O₃, ZnO, PbO) are amphoteric. Example: 4Al + 3O₂ → 2Al₂O₃.
3.Metal + Water
$2 N a + 2 H_{2} O ⟶ 2 N a O H + H_{2} (g)$
Reactivity decreases K > Na > Ca > Mg > Al > Zn > Fe. Mg reacts with hot water, Zn/Fe only with steam. Cu does not react.
4.Metal + Dilute Acid★
$M + 2 H C l ⟶ M C l_{2} + H_{2} (g)$
Metals ABOVE hydrogen in reactivity series liberate H₂ with dilute HCl / H₂SO₄. Cu, Ag, Au do not.
5.Displacement in Salt Solution
$F e + C u S O_{4} ⟶ F e S O_{4} + C u$
More reactive metal displaces less reactive one from its salt solution. Basis of many extraction methods.
6.Amphoteric Oxide
$A l_{2} O_{3} + 6 H C l ⟶ 2 A l C l_{3} + 3 H_{2} O$
Same oxide also reacts with a base: Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O. Hence AMPHOTERIC.
7.Reduction of Metal Oxide (Smelting)★
$Z n O + C ⟶ Z n + C O$
Reduction of moderately reactive metal oxide using carbon (coke). Example: Fe₂O₃ + 3C → 2Fe + 3CO.
8.Thermite Reaction
$F e_{2} O_{3} + 2 A l ⟶ 2 F e + A l_{2} O_{3}$
Highly exothermic; molten iron produced. Used to weld railway tracks and cracked machine parts.
9.Electrolytic Refining
$Impure M (anode) ⟶ M^{n +} (a q) + n e^{-}; M^{n +} + n e^{-} ⟶ M (cathode)$
Pure metal deposits on the cathode; impurities settle as ANODE MUD. Used to purify Cu, Zn, Ag.

Ch 3 · Metals and Non-Metals — Properties Focus

1.Electron-Dot: Sodium Chloride★
$N a^{∙} +_{∙∙}^{∙∙} ∙∙ C l ∙∙^{∙} ⟶ N a^{+} [C l :]^{-}$
Na (2,8,1) donates 1e⁻ to Cl (2,8,7) — both attain the nearest noble-gas configuration.
2.Electron-Dot: Water
$H : O ¨ : H$
Covalent: each H shares 1 pair with O. O has 2 lone pairs. Bent (angular) molecule, 104.5° bond angle.
3.Electron-Dot: Methane
$H : H C H : H$
C shares 4 electron pairs with 4 H atoms — tetrahedral geometry.
4.Reactivity Series (Compact)★
$K > N a > C a > M g > A l > Z n > F e > P b > (H) > C u > H g > A g > A u$
Memorise once and for all. Determines who displaces whom, and whether the metal reacts with water / acid.
5.Metal + Non-metal (Ionic)
$2 N a + C l_{2} ⟶ 2 N a C l$
Ionic compounds — high m.p., soluble in water, conduct in molten/aqueous form.
6.Non-metal + Non-metal (Covalent)
$H_{2} + C l_{2} ⟶ 2 H C l$
Covalent compounds — low m.p., mostly insoluble in water, do not conduct electricity.
7.Amphoteric Oxide Test
$A l_{2} O_{3} + H C l, N a O H ⟶ both react$
An oxide is amphoteric if it dissolves in BOTH acid and base. Common examples: Al₂O₃, ZnO, PbO, SnO.

Ch 4 · Carbon and its Compounds

1.General Formula of Alkane★
$C_{n} H_{2 n + 2}$
Saturated hydrocarbons; all C-C single bonds. Example: methane CH₄, ethane C₂H₆.
2.General Formula of Alkene
$C_{n} H_{2 n}$
Unsaturated; ONE C=C double bond. Example: ethene (ethylene) C₂H₄.
3.General Formula of Alkyne
$C_{n} H_{2 n - 2}$
Unsaturated; ONE C≡C triple bond. Example: ethyne (acetylene) C₂H₂.
4.Combustion of Ethanol
$C_{2} H_{5} O H + 3 O_{2} ⟶ 2 C O_{2} + 3 H_{2} O + heat$
Highly exothermic. Ethanol used as clean fuel additive (petrol + 10 % ethanol).
5.Dehydration of Ethanol★
$C_{2} H_{5} O H conc. H_{2} S O_{4}, 17 0^{\circ} C C_{2} H_{4} + H_{2} O$
Conc. H₂SO₄ is a dehydrating agent — removes H₂O and gives ethene.
6.Oxidation of Ethanol
$C_{2} H_{5} O H alk. K M n O_{4} /Δ C H_{3} C O O H$
Purple KMnO₄ → colourless — a common test. Also happens naturally when wine turns to vinegar.
7.Esterification★
$C H_{3} C O O H + C_{2} H_{5} O H conc. H_{2} S O_{4} C H_{3} C O O C_{2} H_{5} + H_{2} O$
Carboxylic acid + alcohol → sweet-smelling ester. Reversible; conc. H₂SO₄ acts as catalyst.
8.Ester + NaOH (Saponification)
$C H_{3} C O O C_{2} H_{5} + N a O H ⟶ C H_{3} C O O N a + C_{2} H_{5} O H$
'Saponification' = soap-making. Ester + alkali → soap + alcohol.
9.Ethanoic Acid + Sodium Bicarbonate
$C H_{3} C O O H + N a H C O_{3} ⟶ C H_{3} C O O N a + H_{2} O + C O_{2} (g)$
Effervescence of CO₂ turns lime water milky — confirms carboxylic acid group.
10.Soap (Long Chain Sodium Salt)
$C_{17} H_{35} C O O N a$
Sodium stearate — a typical soap. Hydrophobic C₁₇H₃₅ tail (dissolves grease) + hydrophilic COO⁻Na⁺ head (dissolves in water).

Ch 5 · Periodic Classification of Elements

1.Döbereiner's Triad★
$Atomic mass of middle \approx \frac{m _{1} + m _{3}}{2}$
Groups of 3 elements with similar chemical properties, in which the middle element's atomic mass is the arithmetic mean of the other two. Example: Li (7), Na (23), K (39).
2.Newlands' Octaves
$Property (n) \approx Property (n + 8)$
Every 8th element (when arranged by atomic mass) had similar properties — like musical octaves. Worked only up to calcium.
3.Mendeleev's Periodic Law★
$Properties = f (Atomic Mass)$
Properties of elements are a periodic function of their atomic masses. Left gaps for undiscovered elements (eka-aluminium = Ga, eka-silicon = Ge).
4.Modern Periodic Law (Moseley)★
$Properties = f (Atomic Number, Z)$
Properties of elements are a periodic function of their ATOMIC NUMBERS (not masses). Solved most anomalies of Mendeleev's table.
5.Valency Trend
$Valency_{group} = group number (for groups 1-2) or 8 - group number (13-17)$
Group 1 → valency 1; group 2 → 2; group 17 → 1; group 16 → 2. All noble gases → 0.
6.Atomic Size Trend (Period)
$r_{Li} > r_{Be} > \dots > r_{F}$
DECREASES across a period (nuclear charge increases, electrons in same shell).
7.Atomic Size Trend (Group)
$r_{Li} < r_{Na} < r_{K} < r_{Rb} < r_{Cs}$
INCREASES down a group (a new shell is added at every step).