chemical changes

• metal oxides • e.g., magnesium + oxygen -> magnesium oxide

• reactions where metals react with oxygen; • this is because the metals gain oxygen

• oxidation is the both the gaining of oxygen and the loss of electrons • reduction is both the losing of oxygen and the gaining of electrons

• reactions in which both reduction and oxidation happen at the same time

• positive ions

• its tendency to form positive ions • the easier they lose electrons to form positive ions, the more reactive they are. • i.e. a more reactive metal will more easily lose its outer electrons to form a positive ion than a less reactive metal

• in order of their reactivity in a reactivity series

• by reacting the metals with water and with dilute acids

• potassium, sodium, calcium, magnesium, aluminium - more reactive than carbon, extracted by electrolysis • (carbon) • zinc, iron, tin, lead - less reactive than carbon, extracted by reduction • (hydrogen) • copper, silver, gold - very unreactive

• metal hydroxide + hydrogen • e.g. magnesium + water → magnesium hydroxide + hydrogen

• by testing a range of different metals reacting with water, • we can work out a reactivity series from most reactive to least reactive; • we can tell the relative reactivity by comparing how vigorous the reaction with water is. • to quantify this, we can test the temperature change and the rate of production of hydrogen gas. * these values allow us to compare the reactivity of different metals via their reactions with water

• some metals that are less reactive than calcium do not actually react with water at all. • to compare their relative reactivities, they’re reacted with dilute acids.

• salt + hydrogen • e.g. magnesium + hydrochloric acid → magnesium chloride + hydrogen

• as long as the metal is more reactive than hydrogen, it will have a reaction with dilute acids - * this means that we can compare the reactivities of less reactive metals by comparing how vigorous the reactions are • the temperature change and the rate of production of hydrogen

• using a splint test (squeaky pop test) and comparing how loud the squeaky pops are OR • using a gas syringe and comparing volume of hydrogen produced per second

• a more reactive element will displace a less reactive element from its compound

• unreactive (native) metals such as gold are found in the Earth as the pure metal itself; t • this means that these metals don’t need to be chemically extracted because they do not easily react with other elements in the ground e.g. oxygen

• reactive metals like iron and copper are found as compounds (e.g. iron oxide) that require chemical reactions to extract the metal

• extracted from their oxides by reduction with carbon

• a rock containing enough metal to make it economic to extract the metal

• if​ ​sodium​ ​is​ ​oxidised,​ ​it​ ​has​ ​lost​ ​an​ ​electron,​ ​leaving​ ​it​ ​with​ ​a​ ​+1​ ​charge, so​ ​the​ ​ionic​ ​equation​ ​is:​ ​Na​ ​->​ ​Na+​ ​​ ​+​ ​e-​ • if​ ​sodium​ ​+1​ ​ion​ ​is​ ​reduced,​ ​it​ ​has​ ​gained​ ​an​ ​electron,​ ​leaving​ ​it​ ​with​ ​a charge​ ​of​ ​zero,​ ​so​ ​the​ ​ionic​ ​equation​ ​is:​ ​Na​+​​ ​+​ ​e-​ ​​ ​->​ ​Na • remember:​ ​the​ ​charges​ ​on​ ​each​ ​side​ ​of​ ​the​ ​equation​ ​should​ ​add​ ​up​ ​to the​ ​same​ ​number

• e.g.​ ​2Na​ ​+​ ​2HCl​ ​->​ ​2NaCl​ ​+​ ​H2​ • HCl​ ​is​ ​made​ ​up​ ​of​ ​H​+​​ ​and​ ​Cl-​ ​​ ​ions​ ​&​ ​NaCl​ ​is​ ​made​ ​up​ ​of​ ​Na+​ ​​ ​and​ ​Cl-​ ​​ ​ions • looking​ ​at​ ​just​ ​sodium:​ ​2Na​ ​->​ ​2Na+​ ,​ ​ ​so​ ​the​ ​ionic​ ​equation​ ​must​ ​be: 2Na​ ​->​ ​2Na+​ ​​ ​+​ ​2e-​ ,​ ​ ​meaning​ ​sodium​ ​has​ ​lost​ ​electrons​ ​&​ ​has​ ​been oxidised • looking​ ​at​ ​just​ ​chlorine:​ ​2Cl-​ ​​ ​->​ ​2Cl-​ ,​ ​ ​meaning​ ​chlorine​ ​has​ ​not​ ​been oxidised​ ​or​ ​reduced • looking​ ​at​ ​just​ ​hydrogen:​ ​2H​+​​ ​->​ ​H2​ ,​ ​ ​so​ ​the​ ​ionic​ ​equation​ ​must​ ​be: 2H+​ ​​ ​+​ ​2e-​ ​​ ​->​ ​H2​ ,​ ​ ​meaning​ ​hydrogen​ ​has​ ​gained​ ​electrons​ ​so​ ​has​ ​been reduced

• redox - as one substance is reduced, another is oxidised

• e.g.​ ​2HCl​ ​+​ ​Mg​ ​->​ ​MgCl​2​​ ​+​ ​H​2 • magnesium:​​ Mg​​ ->​ ​Mg​2+,​​​ so​​ ionic​ ​equation​​is​​ Mg​​->​​Mg2​+​​​ +​​2e-​,​​​Mg​​ has lost​ ​electrons​ ​so​ ​​Mg​ ​has​ ​been​ ​oxidised • hydrogen:​ ​2H+​ ​​ ​->​ ​H2​ ,​ ​ ​so​ ​ionic​ ​equation​ ​is​ ​2H+​ ​​ ​+​ ​2e-​ ​​ ​->​ ​H2​ ,​ ​ ​H​ ​has​ ​gained electrons,​ ​so​ ​​H​ ​has​ ​been​ ​reduced • because​ ​magnesium​ ​has​ ​been​ ​oxidised​ ​and​ ​hydrogen​ ​has​ ​been​ ​reduced in​ ​the​ ​same​ ​reaction,​ ​this​ ​is​ ​a​ ​​redox​ ​reaction