C4-Chemical Changes

• PH 7 is neutral
• PH 1 is acid
• PH 14 is alkali
• measure PH by using universal indicator
• Acids form H+ ions
• Alkali form OH- ions
• acids produce protons in water
• strong acids like sulfuric, hydrochloric and nitric acids ionise completely in water and release H+ ions
• Weak acids like ethanoic , citric and carbonic acids do not fully ionise in solution and release H+
• factor H+ ion concentration changes by = 10-x
• metal oxides and metal hydroxides are bases
• order of reactivity POTASSIUM, SODIUM, LITHIUM, CALCIUM, MAGNESIUM,CARBON, ZINC, IRON, HYDROGEN, COPPER
• acid + metal --- salt + hydrogen
• metal + water --- metal hydroxide + hydrogen
• oxidation = gain of oxygen
• reduction = loss of oxygen
• formation of metal ore is oxidation = gain of oxygen
• extraction of metal is reduction = loss of oxygen
• some metals can be extracted from their ores chemically by reduction using carbon and in this reaction the ore is reduced as oxygen is removed from it and carbon gains oxygen so is oxidised
• metals higher than carbon in the reactivity series can be extracted by electrolysis
• metals below carbon in the reactivity series can be extracted by reduction using carbon
• if electrons are transfered its a redox reaction
• a loss of electrons is called oxidation
• a gain of electrons is called reduction
• oxidation and reduction happen at the same time
• a more reactive metal will displace a less reactive metal from its compound
• in displacement reactions the metal ions gain electrons and is reduced and the metal atom always loses electrons and is oxidised
• ELECTROLYSIS means splitting up with electricity
• during electrolysis an electric current is passed through an electrolyte and the ions move towards the electrodes where they react and the compound decomposes
• electrolyte is a molten or dissolved ionic compound
• the positive ion in the electrolyte will move towards the cathode ( +VE electrode ) and gain electrons
• the negative ions in the electrolyte will move towards the anode ( -VE electrode ) and lose electrons and this creates a flow of charge through the electrolyte as ions travel to the electrodes
• an ionic solid cant be electrolysed because the ions are set in a fixed position
• molten ionic compound can be electrolysed because the ions can move freely and conduct electricity
• positive metal ions are reduced to the element at the cathode and the negative non metals ions are oxidised to the element at the anode
• metals can be extracted from their ores using electrolysis

  A) negative

  B) positive

  C) non metals form negative ions

  D) positive electrode

  E) metals form positive ions

  F) negative electrode

  
• cathode -VE
• anode +ve
• electrode = an electrical conductor which is submerged in the electrolyte during electrolysis
• electrolysis = the process of breaking down a substance using electricity