chemical changes

• In a redox reaction, electrons are transferred from one atom to another.
• Oxidation involves losing electrons, while reduction involves gaining electrons.
• acids form hydrogen ions in aqueous solutions
• the reaction between acids and bases is called a neutralisation reaction.
• acid + base ---- salt + water
• neutralisation between acids and alkalis cen be seen using H+ and OH- ions
• in displacement reactions a more reactive metal will displace a less reactive one
• more reactive metals are extracted using electrolysis
• less reactive metals can be extracted using carbon
• how metals react with acids tells us about their reactivity
• metal + acid ---> salt + hydrogen gas
• the speed indicates the rate, the more reactive the faster it goes, the less reactive the slower it goes
• metal + water --- metal hydroxide + hydrogen
• oxidation is when an element loses electrons to become more positive
• reduction is when an element gains electrons to become more negative
• electrolysis is splitting up compounds by passing electricity through them
• in electrolysis, the cathode is where reduction happens
• less reactive metals will not react with water
• more reactive metals will react vigorously with water
• acids ionise in aqueous solutions, producing H+
• strong acids ionise completely, all particles dissociate
• weak acids only partially ionise, some particles remain undissociated
• acid strength = what proportion of the acid is dissociated in a solution of that acid
• concentration = how watered down an acid is
• you can still have a dilute, but strong acid
• metal oxides and metal hydroxides are bases
• bases neutralise acids to form salts + water
• neutralisation reactions involve metals reacting with acids or bases reacting with acids
• acid + metal oxide --- salt + water
• acid + metal carbonate --- salt + water + carbon dioxide
• you can make soluble salts using insoluble bases
• in electrolysis the substance has to be molten so that the ions can move freely
• the anode is where positive ions are produced
• electrolysis is used to extract metals from their compounds, purify metals and produce chlorine gas
• the cathode is where negative ions are produced
• aluminum is mixed with cryolite to lower its melting point
• when an anode is made of carbon it has to be replaced as it is used up
• chlorine gas is produced by passing electricity through hydrogen chloride solution