P1 4 Chemical Changes

Oxidation Is Loss, Reduction Is Gain * oxidation - gaining oxygen or losing hydrogen - loss of electrons * reduction - losing oxygen or gaining hydrogen - gain of electrons

the reaction that occurs when a more reactive metal takes a metal’s place in a compound

-a reaction where both oxidation+reduction occur -transfer of electrons eg. displacement * one metal is reduced - forms ions - becomes a compound * other metal is oxidised (displaced) - forms atoms - regains electrons given to non-metal

metal oxide + carbon -> metal + carbon dioxide (used when the metal is less reactive than carbon) zinc, iron, tin, lead metal oxide is heated with carbon, CO2 escapes into surroundings

• unreactive so are found as pure elements • do not need to be extracted by electrolysis/ carbon reduction • copper, silver, mainly gold+platinum

Mg(s) -> Mg2+(aq) + 2e- 2H+(aq) + 2e- -> H₂(g)

Mg(s) + 2H+(aq) -> Mg2+(aq) + H₂(g) (remove 2HNO₃ as it is unchanged by the reaction)

the substance must be dissolved in water/aqueous or molten

H+(aq) + OH-(aq) -> H₂O(l) acid + alkali -> water + SALT

• produce hydrogen ions • as pH number decreases, H+ concentration increases • strong acids will fully ionise (1-3) • weak acids will partially ionise (4-6)

• strong acid are completely ionised in an aqueous solution, high concentration of hydrogen ions (H+) -> hydrochloric acid (HCl), sulfuric (H2SO4), nitric (HNO3) • weak acids are partially ionised in an aqueous solution, less reactive, lower concentration of hydrogen ions -> ethanoic, citric, carbonic acids

• concentrated acid contains a high proportion of acid molecules compared to water molecules in a solution • dilute acid contains a lower proportion of acid molecules compared to water molecules • adding water to a strong acid dilutes it (but is still strong)

• produce hydroxide ions • as pH number increases, OH- concentration increases • strong alkalis will fully ionise (pH 11-14) • weak acids will partially ionise (8-10)

• universal indicator • yellow litmus paper • red litmus paper: stays red for acidic, stays red for neutral, turns blue for alkaline • blue litmus paper: turns red for acidic, stays blue for neutral, stays blue for alkaline

• increase 10-fold • pH1 is 10x more acidic than pH2 • pH13 is 10x less alkaline than pH14

acid + metal -> salt + hydrogen acid + alkali -> salt + water (neutralisation) acid + metal oxide -> salt + water acid + metal hydroxide -> salt + water

metals more reactive than carbon are extracted from compounds ions are discharged at the electrodes to form atoms: * positive metal ions travel to the cathode - they gain electrons to form a neutral atom/element (reduction) * negative non-metal ions travel to the anode - they lose electrons to become a neutral atom/element (oxidation)

/ electrodes are made of carbon (graphite)- delocalised electrons so conduct electricity / electrodes are inert so don’t form ions during electrolysis X requires a lot of energy to melt the compounds+ produce electric current - expensive -> substances with a high melting point (bauxite) are dissolved in molten cryolite to lower the substance’s melting point X when oxygen is formed at the anode it reacts with the carbon electrodes to form CO2 - anodes have to be frequently replaced

• bauxite is insoluble in water so must be molten to act as an electrolyte • bauxite has a high melting point - a lot of energy is required to break its strong ionic bonds - expensive • to reduce costs it is dissolved in molten cryolite - ionic compound melts at a lower temp than bauxite

• substance is melted so ions are free to move • positive metal ions travel to the cathode - they gain electrons to become a neutral element • negative non-metal ions travel to the anode - they lose electrons to become a neutral element • Positive Anode, Negative Is Cathode

• hydrogen is produced at the cathode if the metal is more reactive than hydrogen, otherwise the metal is produced • oxygen is produced at the anode unless the non-metal is a halogen, otherwise the halogen gas is produced

• measure a vol. of dilute (sulphuric) acid using a measuring cylinder and pour into a beaker • set up a bunsen burner/tripod/gauze then heat beaker over a gentle flame until acid is almost boiling • remove from heat and add base (copper oxide) until it is in excess, stir with glass rod • filter mixture into conical flask using filter paper/funnel • pour solution into evaporating basin and warm over a water bath, then leave to cool until crystals form

• hot apparatus - don’t touch when hot • bunsen burner - tie hair/tuck loose clothing to prevent catching fire • sulphuric acid - concentrated acid is corrosive and damages skin/clothes - use dilute acid, use copper oxide in excess so no acid remains on the salt

forms metal hydroxide (s) + hydrogen (g) * bubbles/ fizzes * moves on surface of water * metal disappears/ melts * hydrogen may ignite -> orange flame (sodium) -> explosion (potassium) (faster reaction down the group)