Chemical reactions involve electrons and where they move (if they move). Metal atoms (or elements) usually give away their outer shell electrons in reactions to become stabilised (creating positive ions). Non-metal atoms (or elements) usually gain electrons in order to become stable (negative ions). Some reactions involve covalent bonds, metallic bonds, ionic bonds etc., but at the base (no pun intended :D) of most chemical reactions it's just a matter of electrons moving around between atoms.
You can identify the aldehyde from acidic potassium permanganate. Purple colour of acidic potassium permanganate is changed to colourless because aldehyde is oxidized by acidic potassium permanganate.
The copper oxide can then react with the hydrogen gas to form the copper metal and water. When the funnel is removed from the hydrogen stream, the copper was still be warm enough to be oxidized by the air again.
chemicals symbols are used for abbreviating the name of the element/chemical while chemicals formulas tell you how much of each element are in each chemical atom
