861 past contests
Topic 7 · Unusual oxidation state of oxygen in hydrogen peroxide (true/false)
Topic 7 · Maximum oxidation state of iodine in periodic acid (true/false)
Topic 23 · True or false: isomerism, optical activity and oxidation resistance of 2-methyl-2-propanol
Topic 21 · Problem of the day: fractional distillation of a two-solvent mixture
Topic 7 · Balancing the roasting equation of iron pyrites
Topic 7 · Balancing a redox equation: permanganate oxidizing oxalate in acid
Topic 7 · Balancing a redox equation: dichromate oxidizing iron(ii) in acid
Topic 10 · Explaining an exothermic dissolution of concentrated sulfuric acid in water
Topic 10 · Explaining an endothermic dissolution via lattice versus hydration energy
Topic 10 · Energy changes (lattice energy and hydration energy) on dissolving an ionic solid
Topic 5 · Reagent converting ethene to a 1,2-dihaloalkane
Topic 5 · Reagent converting ethene to chloroethane
Topic 5 · Reagent converting ethene to ethylene glycol via cold dilute kmno4
Topic 29 · Why attractive force on valence electrons increases across a period
Topic 29 · Why first ionization energy decreases down a group
Topic 29 · Why first ionization energy increases across a period
Topic 37 · Riddle: heavy water (d2o) as a triatomic binary compound
Topic 15 · Catalysts are chemically unchanged at the end of a reaction (true/false)
Topic 15 · Homogeneous catalysts are not inhibitors (true/false)
Topic 15 · The rule-of-thumb temperature rise that doubles reaction rate (true/false)