P1 4 Chemical Changes Flashcards
describe oxidation and reduction
Oxidation Is Loss, Reduction Is Gain
* oxidation - gaining oxygen or losing hydrogen - loss of electrons
* reduction - losing oxygen or gaining hydrogen - gain of electrons
describe displacement
the reaction that occurs when a more reactive metal takes a metal’s place in a compound
describe a redox reaction
eg. displacement
* one metal is reduced - forms ions - becomes a compound
* other metal is oxidised (displaced) - forms atoms - regains electrons given to non-metal
state the equation for when a metal (oxide) is extracted from an ore using carbon reduction
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
define native metals
- unreactive so are found as pure elements
- do not need to be extracted by electrolysis/ carbon reduction
- copper, silver, mainly gold+platinum
construct 2 half equations for the equation:
Mg(s) + 2H+(aq) -> Mg2+(aq) + H₂(g)
Mg(s) -> Mg2+(aq) + 2e-
2H+(aq) + 2e- -> H₂(g)
reconstruct the equation without spectator ions:
Mg(s) + 2H+(aq) + 2HNO₃(aq) -> Mg2+(aq) + 2HNO₃aq) + H₂(g)
Mg(s) + 2H+(aq) -> Mg2+(aq) + H₂(g)
(remove 2HNO₃ as it is unchanged by the reaction)
what is required to split up ionic substances into ions
the substance must be dissolved in water/aqueous or molten
state the equation for neutralisation
H+(aq) + OH-(aq) -> H₂O(l)
acid + alkali -> water + SALT
describe acids when dissolved in a solution (water)
- produce hydrogen ions
- as pH number decreases, H+ concentration increases
- strong acids will fully ionise (1-3)
- weak acids will partially ionise (4-6)
describe the 3 differences between strong+ weak acids (+exs)
- 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
describe the difference between concentrated+dilute 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)
describe alkalis when dissolved in a solution (water)
- 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)
describe indicators used to test acids+alkalis (4)
- 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
describe the scale used for pH levels
- increase 10-fold
- pH1 is 10x more acidic than pH2
- pH13 is 10x less alkaline than pH14
state 4 equations that form salts
acid + metal -> salt + hydrogen
acid + alkali -> salt + water (neutralisation)
acid + metal oxide -> salt + water
acid + metal hydroxide -> salt + water
describe the process of electrolysis
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)
describe the pros+cons of apparatus used for electrolysis
/ 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
why is molten cryolite used in the electrolysis of bauxite (aluminium oxide/ ore)
- 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
describe products of electrolysis of molten ionic compounds
- 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
describe products of electrolysis of aqueous ionic solutions
- 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
describe the method for RP: making salts/neutralisation
- 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
describe precautions for RP: making salts/neutralisation
- 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
what is seen when alkali metals react with water (4)
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)
what is seen when alkali metals react with chlorine (+halogens) (2)
forms metal chloride
* forms a white solid
* * burns with a flame
-> lithium: red
-> sodium: yellow
-> potassium: lilac
(faster reaction down the group)
what is seen when alkali metals react with oxygen (2)
forms metal oxide
* tarnishing - forms a dull+white solid
* burns with a flame
-> lithium: red
-> sodium: yellow
-> potassium: lilac
(faster reaction down the group)
state the reactivity series inc. carbon+ hydrogen
potassium (easiest to lose electrons+ form pos ions)
sodium
lithium
calcium
magnesium
aluminium
-> carbon
zinc
iron
tin
lead
-> hydrogen
copper
silver
gold/ platinum
state the equation for when a metal reacts with an acid
metal + acid -> salt + hydrogen
describe the reaction between metals and dilute acids
alkalis: (potassium, sodium, lithium): react vigorously, form salt solution+ hydrogen
(calcium, magnesium, zinc, iron): react more slowly, form salt solution+ hydrogen
(copper): no reaction, no products
state the equation for when a (more reactive) metal reacts with water
metal + water -> metal hydroxide + hydrogen
state the equation for when a (less reactive) metal reacts with water
metal + water -> metal oxide + hydrogen
describe the reaction between metals and water
(potassium, sodium, lithium, calcium): react quickly/vigorously, form metal hydroxide+ hydrogen
(magnesium, zinc, iron): react slowly or not at all with cold water, form hydrogen+ metal oxide (with steam)
(copper): no reaction, no products
state the equation for when a metal carbonate reacts with an acid
acid + metal carbonate -> salt + water + carbon dioxide
(neutralisation)- metal carbonates are bases
