Recognizing chemical-reaction patterns and transformations.
Test your knowledge with these top questions!
Which color best describes common rust on iron objects?
The reddish tint comes from iron oxides, the same compounds that give Mars its red color.
Which compound makes up common red rust?
Rust is a hydrated iron oxide: water molecules are part of its crystal structure, not just something sitting on the surface.
Rust forms when iron reacts with oxygen and which other substance?
Salt does not cause rust by itself, but dissolved salt helps water carry an electric current, so cars rust faster after winter road salting.
Galvanized iron is protected from rust by a coating of which metal?
Zinc keeps working even after the coating is scratched because it corrodes first, unlike tin plating, which lets the iron underneath rust faster.
What is the breaking away of concrete caused by expanding rust on reinforcing steel called?
Concrete normally protects steel with its high alkalinity; chloride salts can break down that protection and allow rusting.
Why does the Statue of Liberty look green?
The statue's thin copper sheets reacted with damp sea air to form the green coating.
During water electrolysis, which gas forms at the negative electrode?
Hydrogen ions gain electrons at the negative cathode, so hydrogen bubbles there while oxygen forms opposite.
What form of energy drives chemical changes during electrolysis?
Electrolysis pushes electrons through a solution, forcing a reaction that would not run on its own.
What does soap help water wash off greasy hands?
Without soap, water beads up on grease instead of lifting it away.
Heated limestone breaks down into carbon dioxide and which solid called quicklime?
Cement makers heat limestone to produce quicklime, a key ingredient in concrete and mortar.