chemical changes

• what is formed when a metal reacts with oxygen?

  metal oxide
• oxidation reaction

  gaining oxygen. e.g magnesium + oxygen ---> magnesium oxide. the magnesium atoms have been oxidised
• reduction reaction

  losing oxygen. e.g magnesium oxide --> magnesium + oxygen. the magnesium atoms have been reduced
• in calcium + copper oxide --> calcium oxide + copper, which element is being oxidised and which is being reduced?

  calcium is being oxidised as it gains oxygen, and copper is being reduced as it loses oxygen
• what is formed when a metal reacts with water?

  a metal hydroxide/alkali with hydrogen. e.g potassium + water --> potassium hydroxide + hydrogen
• how can we arrange metals in order of their reactivity?

  by reacting them with water and judging how quickly they react
• reactions of metals with water

  potassium react very rapidly with water at room temperaturesodiumlithiumcalcium reacts quite rapidly with water at room temperaturemagnesium no reaction with water at room temperaturezincironcopper
• reactions of metals with dilute acid

  potassium dangerously fast reactions with acids sodium lithium calcium extremely vigorous reactionmagnesium rapid reactionzinc quite rapid reactioniron quite slow reactioncopper no reaction
• reactivity series


  potassium, sodium, lithium, calcium, magnesium, carbon, zinc, iron, hydrogen, copper
• the reactivity of a metal...

  depends on its ability to lose electrons and form a positive ion
• gold


  unreactive metals such as gold are found in the earth as the metal
• iron oxide + copper oxide

  -found in earth's crust

  -iron and copper have reacted with oxygen to form compounds

  -need to be extracted
• a more reactive element will...

  displace a less reactive element from its compound
• what would happen if magnesium reacted with iron oxide?

  magnesium woulddisplaceiron as it's more reactive. the products of the reaction would be magnesium oxide + iron. the iron atoms have also been reduced as they've lost oxygen. the magnesium atoms have been oxidised as they've gained oxygen
• extractions of metals using carbon

  -carbon used to displace elements as it's on the higher end of the reactivity series and even more reactive elements are expensive

  e.g iron oxide + carbon ---> carbon dioxide + iron
• oxidation (in terms of electrons)


  loss of electrons
• reduction (in terms of electrons)


  gain of electrons
• in the half equation Al --> Al3+ + 3e- what is happening?

  aluminium is being oxidised as it's losing electrons
• in the half equation O + 2e- --> O2- what is happening?

  oxygen is being reduced as it's gaining electrons
• in the reaction zinc + copper sulfate --> zinc sulfate + copper what has been reduced and what has been oxidised?


  zinc has been oxidised, it started as an atom but became an ion meaning it had to lose electrons. copper has been reduced, it started as an ion but became an atom meaning it had to gain electrons.
• what does aq mean?

  aqueous solution (dissolved in water)
• acids


  produce hydrogen ions (H+) in aqueous solutions.

  e.g:

  -HCl (aq) --> H+ (aq) + Cl- (aq)

  -H2SO4 (aq) --> 2H+ (aq) + SO42-

  -HNO3 (aq) --> H+ (aq) + NO3-
• bases


  chemicals which can neutralise acids and produce a salt + water

  -usually metal oxides or metal hydroxides
• alkalis


  bases which are soluble in water

  -e.g sodium hydroxide

  aqueous solutions of alkalis contain hydroxide ions OH- e.g

  -NaOH (aq) --> Na+ (aq) + OH- (aq)
• pH scale


  -tell us the acidity or alkalinity of a solution

  -to determine pH we can use:

  a pH probe or universal indicator
• what happens when an acid is reacted with an alkali? (neutralisation reaction)

  the hydrogen ions in the acid and the hydroxide ions in the alkali react to form water e.g

  H+ (aq) + OH- (aq) --> H2O (l)
• what happens when an acid reacts with a metal?

  a salt and hydrogen is produced
• all metals more reactive than hydrogen can...

  displace hydrogen from acids. hydrogen is in all acids

  e.g sulfuric acid + magnesium --> magnesium sulfate + hydrogen
• hydrochloric acid produces salts that end in...

  chloride
• nitric acid produces salts that end in...

  nitrate
• sulfuric acid produces salts that end in...

  sulfate
• reaction of hydrochloric acid and magnesium

  hydrochloric acid + magnesium --> magnesium chloride + hydrogen
• in the reaction of hydrochloric acid + zinc --> zinc chloride + hydrogen , what is being reduced and what is being oxidised?

  zinc is being oxidised as it loses electrons and goes from an atom to an ion, hydrogen is being reduced as the hydrogen ion gains electrons and becomes an atom
• rate of reaction with dilute acids

  -magnesium has a very rapid reaction as it easily forms mg2+

  -zinc has quite a rapid reaction as it quite easily forms zn2+

  -iron reacts slowly as it less easily forms fe2+
• when we react an acid with either a base or an alkali we make a...

  salt and water. e.g

  -hydrochloric acid + copper oxide --> copper chloride + water

  -hydrochloric acid + sodium hydroxide --> sodium chloride + water
• salts


  -contain a positive ion which comes from the base or alkali

  -contain a negative ion which comes from the acid
• when acids react with a metal carbonate...

  they make a salt, water and carbon dioxide e.g

  -hydrochloric acid + sodium carbonate -> sodium chloride + water + carbon dioxide

  -hydrochloric acid + calcium carbonate -> calcium chloride + water + carbon dioxide
• in aqueous solutions, acid molecules...

  ionise (split) and release H+ (hydrogen)
• strong acids

  fully ionise in aqueous solutions
• 3 strong acids

  HCl, H2SO4 , HNO3 (hydrochloric acid , sulfuric acid and nitric acid)