Maharashtra HSC Chemistry flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Unit cell density formula

Density d = Z·M/(a³·N_A), where Z is the number of atoms per unit cell, M the molar mass, a the edge length in cm and N_A Avogadro's number.

Schottky vs Frenkel defect

Schottky defect is a cation-anion vacancy pair that lowers crystal density; Frenkel defect is a cation displaced to an interstitial site, leaving density unchanged.

van't Hoff factor

i equals the observed colligative property divided by the value calculated for a non-electrolyte; it is greater than 1 for dissociation and less than 1 for association.

Colligative properties

Properties depending only on the number of solute particles, not their identity: relative lowering of vapour pressure, boiling point elevation, freezing point depression and osmotic pressure.

Henderson–Hasselbalch equation

For an acidic buffer, pH = pKa + log([salt]/[acid]); for a basic buffer, pOH = pKb + log([salt]/[base]). Buffer capacity is maximum when salt and acid concentrations are equal.

Solubility product Ksp

The equilibrium constant for dissolution of a sparingly soluble salt; for a 1:1 salt such as AgCl, Ksp = s², where s is molar solubility. Precipitation occurs when the ionic product exceeds Ksp.

Gibbs energy criterion

At constant temperature and pressure, ΔG = ΔH − TΔS; a negative ΔG means the process is spontaneous, zero means equilibrium and positive means non-spontaneous.

Hess's law

The enthalpy change of a reaction is the same whether it occurs in one step or several steps, so ΔH can be calculated from standard enthalpies of formation of reactants and products.

Nernst equation

At 298 K, E = E° − (0.0592/n)·log Q, relating electrode potential to standard potential, number of electrons transferred and reaction quotient Q.

Kohlrausch law of independent migration

The limiting molar conductivity of an electrolyte equals the sum of the limiting ionic conductivities of its ions; used to find the degree of dissociation of weak electrolytes.

First-order half-life

For a first-order reaction, t½ = 0.693/k, which is independent of the initial reactant concentration; after each half-life, the remaining fraction is halved.

Arrhenius equation

k = A·e^(−Ea/RT), showing that the rate constant rises with temperature and decreases with activation energy; A is the pre-exponential factor and Ea the activation energy.

Acid strength of oxoacids

For chlorine oxoacids, acidity increases with the number of oxygen atoms: HClO < HClO₂ < HClO₃ < HClO₄, because the conjugate base is better stabilised by resonance.

Interhalogen compounds

Compounds formed between two different halogens, such as ClF₃, BrF₅ and ICl; the larger or less electronegative halogen is central and forms higher fluorides.

Lanthanoid contraction

The steady decrease in atomic and ionic radii from lanthanum to lutetium due to poor shielding of nuclear charge by 4f electrons, making lanthanoid chemistry very similar.

KMnO₄ in acidic medium

In acidic solution, permanganate is reduced from Mn(VII) to Mn(II), a five-electron change; the purple colour fades to pale pink or colourless.

Crystal field splitting

Splitting of metal d-orbitals in an octahedral field into lower t₂g and higher e_g sets by energy Δo; strong-field ligands give large splitting and low-spin complexes.

Chelate effect

Polydentate ligands such as EDTA and ethylenediamine form more stable complexes than comparable monodentate ligands because of favourable entropy of chelation.

SN1 vs SN2 mechanism

SN1 is a two-step, first-order reaction via a carbocation, favoured by tertiary halides; SN2 is a one-step, second-order backside displacement, favoured by primary halides.

Lucas test

A test with concentrated HCl and anhydrous ZnCl₂: tertiary alcohols turn cloudy immediately, secondary in about five minutes, primary not at room temperature.

Williamson synthesis

An ether is prepared by reacting a sodium alkoxide with a primary alkyl halide; tertiary halides give mainly elimination products instead of ethers.

Tollens' test

A mild oxidation using ammoniacal silver nitrate; aldehydes reduce Ag⁺ to metallic silver, giving a mirror on the test tube, while ketones do not react.

Cannizzaro reaction

Disproportionation of aldehydes lacking α-hydrogen, such as formaldehyde and benzaldehyde, in strong base, giving one molecule of alcohol and one of carboxylic acid salt.

Hinsberg test

Benzenesulphonyl chloride reacts with primary amines to give an alkali-soluble product, with secondary amines an insoluble product, and does not react with tertiary amines.

Hofmann bromamide degradation

A primary amine with one carbon fewer is prepared from an amide by treatment with bromine and alkali; the reaction gives a pure primary amine without secondary or tertiary contamination.

Reducing vs non-reducing sugars

Reducing sugars such as glucose, maltose and lactose have a free anomeric hydroxyl group and reduce Tollens' and Fehling's reagents; sucrose is non-reducing.

Denaturation of proteins

Loss of secondary and tertiary structure by heat, pH change or urea, without breaking peptide bonds; the protein loses biological activity and may coagulate.

Condensation polymerisation

Polymer formation with elimination of a small molecule such as water or HCl; examples are nylon-6,6 from adipic acid and hexamethylenediamine, and PET from a diol and diacid.

Vulcanisation

Heating natural rubber with sulphur forms cross-links between polymer chains, making the rubber stronger, harder and more elastic and less sensitive to temperature.

Atom economy

Atom economy = (molar mass of desired product / total molar mass of reactants) × 100%, measuring how much of the reactant mass ends up in the desired product.

Nanoparticle size range

Nanoparticles have at least one dimension between 1 and 100 nanometres, giving a very large surface-area-to-volume ratio and size-dependent optical, catalytic and magnetic properties.

Bragg's law

nλ = 2d sinθ relates X-ray wavelength, interplanar spacing d and angle of diffraction θ; used to determine crystal structures.

Thermoplastic vs thermosetting polymer

Thermoplastics soften on heating and can be remoulded, such as polythene and PVC; thermosetting polymers cross-link permanently and char instead of melting, such as bakelite.