C4: Chemical Changes Flashcards
define oxidation and reduction
oxidation: when a substance gains oxygen / loses electrons
reduction: when a substance loses oxygen/ gains electrons
what is the reactivity series of metals?
A list of elements ordered by their reactivity
what are the trends in reactivities of metals in reactions with acids/water?
- metals above hydrogen in reactivity series react with acid to produce hydrogen
- The more reactive the metal is, the quicker and more violent reaction with acid occurs
- metals below H2 dont react with acids
- not all metals above H2 react with water
Write the reactivity series from
most reactive to least reactive
potassium
sodium
calcium
magnesium
aluminium
carbon
zinc
iron
tin
lead
hydrogen
copper
silver
gold
platinum
what is a displacement reaction?
- a reaction where a more reactive metal displaces a less reactive metal from a compound
how are unreactive metals found in Earth?
in their natural state
Explain why zinc can be
extracted from zinc oxide with
carbon but magnesium cannot
be extracted from magnesium
oxide with carbon
Magnesium is more reactive than carbon (1), Zinc is less reactive than carbon (1), Carbon can therefore remove oxygen from zinc oxide but not magnesium oxide (1
What process is used to extract
metals more reactive than
carbon
Electrolysis
how can metals less reactive then carbon be extracted?
- reduction with carbon
- Carbon displaces the metal in a metal oxide
- Carbon gets oxidised to form carbon oxides .
- Metal from the metal oxide gets reduced to the pure metal
- eg Copper oxide + carbon → copper + carbon dioxide
what is the general equation for a reaction between metals and acids? what type of reaction is this?
metal + acid –> salt + hydrogen
redox reaction, also a displacement reaction
which metals in the reactivity series will react with acid?
those above hydrogen
what is the general equation for a neutralisation reaction?
Base + acid –> salt + water
what is the general equation for the reaction between metal carbonate and acid?
- metal carbonate + acid—>salt + water + carbon dioxide
what is the general equation for the reaction between metal oxides and acids?
metal oxide + acid—> salt + water
what is a redox reaction?
- a reaction where both oxidation and reduction occurs
explain in terms of gain or loss of electrons which species has been oxidised and which species has been reduced when magnesium reacts with hydrochloric acid
magnesium has lost electrons and thus has been oxidised (Mg to MG2+)
- the hydrogen in HCL has gained electrons and thus has been reduced (H+ to H2)
how is a soluble salt formed?
- react the excess acid with some insoluble chemical (e.g. metal oxide)
- filter off the leftovers
- Crystallise the product
what do acids and alkalis produce in aqueous solutions?
- acids produce hydrogen ions, alkalis produce hydroxide ions
define bases , acids and alkalis?
- bases are compounds that neutralise acids
- acids produce hydrogen ions in aqueous solutions
- alkalis are soluble bases - produce hydroxide ions in aqueous solutions
what is the pH scale and what does a pH of 7 show?
- the measure of acidity/ alkalinity of a solution
- a neutral solution
state the general equation for a neutralisation reaction in a short, ionic form
H* + OH- –> h20
what is a strong acid? what is a weak acid?
- strong acid is completely ionised in aqueous solution
- weak acid is only partially ionised in aqueous solution
what happens to pH as concentration of H+ increases?
- the pH decreases
what is a concentrated acid and what is a dilute acid? is this the same as a strong and weak acid?
- concentrated acid has more moles of acid per unt volume than dilute acids
- it is not the same - strength refers to whether the acid is completely ionised in water
As the pH is decreased by one unit , what change is seen in the hydrogen ion concentration
increases by a factor of 10
name the following salts:
- LiNO3
- K2CO3
- MgBr2
- BaSO4
- lithium nitrate
- potassium carbonate
- magnesium bromide
- barium sulfate
what is electrolysis?
- the passing of an electric current through ionic substances that are molten to break them down into elements
- ions are discharged (they lose/gain electrons) at electrodes to produce these
what is an electrolyte?
the liquid/solution which conducts electricity
what is a cathode and what is an anode?
cathode is the negative electrode
anode is the positive electrode
what occurs at the cathode and what occurs at the anode during electrolysis?
reduction occurs at the cathode
oxidation occurs at the anode
in aqueous electrolysis, which element is discharged at the cathode?
- the less reactive element discharges at the cathode.
- hydrogen is produced unless there is a less reactive metal
- in which case the said metal is produced
how is aluminium manufactured? why is it expensive?
- aluminium is made through the electrolysis of aluminium oxide and cryolite
- lots of energy is needed to produce the current in electrolysis which makes this process expensive
what are the half equations in the extraction of aluminium?
cathode: Al3* + 3e- –> Al(cathode)
anode: 2O 2- → O 2 + 4e -( anode)
oxygen reacts with Carbon of the anode producing CO2-
why is cryolite used in manufacturing of aluminium
- it lowers the melting point of aluminium oxide, reducing energy costs
what are the half equations in electrolysis of the aqueous Na2SO4?
2H* + 2E- –> H2 (cathode)
4OH- –> 2H20 + 02 + 4e- (anode)
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what are the half equations in electrolysis of the aqueous CuBr2
Cu2* + 2e- —> Cu (cathode)
2Br- –> Br2 + 2e-
define an ore
material containing enough metal in it for it to be economically worthwhile to extract the metal.
give the empirical formulae for
- hydrochloric acid
- sulfuric acid
- nitric acid
- HCl
- H₂SO₄
- HNO₃
describe what occurs at the anode in the electrolysis of aqueous solutions
- negatively charged OH– ions and non-metal ions are attracted to the positive electrode
- If halide ions (Cl-, Br-, I-) and OH- are present then the halide ion is discharged at the anode, loses electrons and forms a halogen (chlorine, bromine or iodine)
- If no halide ions are present, then OH- is discharged at the anode, loses electrons and forms oxygen
describe what occurs in the cathode in the electrolysis of aqueous solutions
- Positively charged H+ and metal ions are attracted to the negative electrode
- If the metal is above hydrogen in the reactivity series, then hydrogen will be produced and bubbling will be seen at the cathode
