JEE · Chemistry doubts
232 doubts found
What does “The mole” actually mean in Some Basic Concepts (Mole Concept), and why does it matter for JEE?
a counting unit for particles — one mole is 6.022×10²³ (Avogadro's number) of anything.
What does “Quantum numbers” actually mean in Structure of Atom, and why does it matter for JEE?
four numbers (n, l, m, s) that pin down an electron's shell, subshell, orbital orientation and spin.
What does “Octet rule” actually mean in Chemical Bonding & Molecular Structure, and why does it matter for JEE?
atoms tend to gain, lose or share electrons to reach eight in their outer shell.
What does “Enthalpy (H)” actually mean in Chemical Thermodynamics, and why does it matter for JEE?
the heat content at constant pressure; ΔH is negative for exothermic and positive for endothermic reactions.
What does “Dynamic equilibrium” actually mean in Equilibrium, and why does it matter for JEE?
the state where forward and reverse reactions occur at equal rates, so concentrations stay constant.
What does “Oxidation and reduction” actually mean in Redox Reactions, and why does it matter for JEE?
oxidation is loss of electrons and reduction is gain of electrons (remember OIL RIG).
What does “Atomic radius trend” actually mean in Periodic Table & Periodicity, and why does it matter for JEE?
atomic size decreases across a period (more nuclear pull) and increases down a group (new shells).
What does “Order of reaction” actually mean in Chemical Kinetics, and why does it matter for JEE?
the power to which a reactant's concentration is raised in the experimentally-determined rate law.
What does “Types of cells” actually mean in Electrochemistry, and why does it matter for JEE?
a galvanic cell turns a spontaneous reaction into electricity; an electrolytic cell uses electricity to drive a non-spontaneous reaction.
What does “Inductive effect” actually mean in Organic Chemistry — Basic Concepts, and why does it matter for JEE?
a permanent shift of electron density through sigma bonds due to electronegativity differences.
What does “Saturation” actually mean in Hydrocarbons, and why does it matter for JEE?
alkanes are saturated (only single bonds); alkenes and alkynes are unsaturated (double or triple bonds).
Why do people spread salt on icy roads and footpaths in winter?
Salt lowers the freezing point of water — a colligative effect.
Diamond and graphite are both pure carbon — why is one the hardest natural material and the other soft enough to write with?
It's the bonding arrangement.
Why does a sealed bag of chips puff up in the sun or on a mountain flight?
Two gas laws are at work.
Why is hydrated copper sulfate bright blue, but it turns white when you heat it dry?
In the hydrated salt, water molecules act as ligands around the Cu²⁺ ion, splitting its d-orbitals so it absorbs red/orange light and reflects blue (crystal field theory).
How do I decide whether a reaction will go by SN1 or SN2?
Look at the substrate first.
Why is phenol acidic enough to react with NaOH, but ordinary ethanol is not?
Both can lose the O–H proton, but the stability of what's left decides the acidity.
How can a simple test tube reaction tell an aldehyde apart from a ketone?
Aldehydes are easily oxidised, ketones are not — and two tests exploit this.
Why does egg white turn solid and opaque when you cook it (or add acid)?
Egg white is mostly protein folded into a precise 3-D shape held by relatively weak bonds (hydrogen bonds, disulfide and ionic links).
I keep getting “The mole” questions wrong in Some Basic Concepts (Mole Concept). What's the trap?
confusing number of moles with number of grams or molecules.
I keep getting “Quantum numbers” questions wrong in Structure of Atom. What's the trap?
confusing the principal quantum number n (shell) with l (subshell).
I keep getting “Octet rule” questions wrong in Chemical Bonding & Molecular Structure. What's the trap?
forcing an octet on exceptions like BeCl₂, BF₃ or SF₆.
I keep getting “Enthalpy (H)” questions wrong in Chemical Thermodynamics. What's the trap?
getting the sign of ΔH the wrong way round.
I keep getting “Dynamic equilibrium” questions wrong in Equilibrium. What's the trap?
thinking the reaction has stopped at equilibrium.