C5 Chemical changes

• metals are often not found natively as pure metals
• metals have to be extracted from their ore
• and ore is a rock containing enough metal to make it economical to extract
• oxidation is adding oxygen
• to extract metals er have to remove oxygen which is called reduction
• to determine reactivity of metals we first look at their reactions with water
• only the most reactive metals react with water
• metal + water -> metal oxide + hydrogen
• potassium, sodium, lithium, calcium, magnesium, aluminium, zinc, iron, copper, silver, gold (reactivity series)
• if metals don't react with water we look at their reactions with dilute acids to decide their reactivity
• metal + acid -> salt + hydrogen
• the least reactive metals react with neither water nor acid
• displacement reaction is when a more reactive elememt displaces a less reactive element in it's compound
• the more reactive a metal is the easier it is to loose or gain it's outer electrons to form ions
• an ionic equation shows only the atoms and ions that change state in a reaction
• oxidation looses electrons
• reduction gains electrons
• half equations shows the movements of electrons when a chemical reaction takes place
• because oxidation and reduction both happen in displacement reactions they are called rebox reactions
• whether extracting a particular metal is worth it depends on 1. how easy it is to extract 2. how much metal the ore contains 3. the commercial demand for the metal
• the two main types of extraction are electrolysis and reduction
• electrolysis uses electricity to extract metals from their ores
• reduction removes oxygen by heating a more reactive element
• the most reactive metals are extracted by electrolysis but less reactive metals can be extracted by reduction
• reactions between and acids can only happen when the metal is more reactive that the hydrogen in the acid
• a salt is a compound formed when the hydrogen in an acid is wholly or partially replaced by metal ions
• one way to make a salt is by reacting acids with metals that are more reactive than hydrogen
• 1. measure 40cm3 of sulphuric acid and gently heat it in a beaker over a bunsen burner 2. slowly add small amounts of copper oxide until it is in excess and allow it to cool 3. filter the solution into an evaporating basin 4. using a water bath, gently start to evaporate the liquid until crystals start to form around the edge 5. leave the rest to cool and form crystals.
• alkalis are part of a bigger group called bases
• all alkalis are soluble in water but some bases are insoluble
• base + acid -> salt + water
• bases neutralise acids and include metal oxides and metal hydroxides
• pH stands for power hydrogen
• a strong acid's ions ionise (split up) fully during a reaction
• the concentration of H+ ions in a solution = the concentration of he acid
• a high concentration of H+ ions gives a low pH
• strong acids are corrosive so are diluted down for use and are only irritants
• weak acids don't fully ionise when dissolved in water so don't form an equilibrium
• pH scale is a logarithmic scale so if you decrease the concentration of H+ ions by a power of 10 the pH increases by 1