861 past contests
Topic 23 · Counting positional isomers of a straight-chain alkanol
Topic 14 · Riddle: uranium, a radioactive heavy metal
Topic 14 · Collecting ammonia gas by downward displacement of air
Topic 14 · Collecting hydrogen chloride gas by upward displacement of air
Topic 16 · Problem of the day: separating a colored solid mixture by column chromatography
Topic 2 · Counting sigma and pi bonds in an alkyne
Topic 2 · The carbon-oxygen double bond (sigma + pi) in alkanones
Topic 34 · Color of the precipitate from potassium hexacyanoferrate(ii) and iron(iii)
Topic 14 · Observation when hydrogen sulfide is bubbled through neutral iron(ii) solution
Topic 31 · Naming elements from their chemical symbols: w (tungsten) and tl (thallium)
Topic 25 · The carbocation: an organic species with a positive charge on carbon
Topic 25 · The free radical: a species with an unpaired electron
Topic 15 · Gas diffusion rate increases with temperature
Topic 22 · Acid functional groups differ between soapy and soapless detergents
Topic 6 · Gas solubility in water decreases with increasing temperature
Topic 22 · Soaps and synthetic (soapless) detergents are chemically distinct
Topic 19 · Percentage composition by mass of an element in a compound
Topic 14 · Riddle: the periodic table of elements
Topic 1 · Problem of the day: mass of a limiting-reagent product across a two-step synthesis with fractional yields