2024-05-11T14:33:57+03:00[Europe/Moscow] en true <p>how to predict what substance gets liberated @ each electrode during electrolysis</p>, <p>where do electrons flow in electrolysis?</p>, <p>how to solve qualitative electrolysis?</p>, <p>formulas to calculate amount of substance liberated</p>, <p>what is the relationship between Q=It=n<sub>e</sub>F and amount of product formed?</p>, <p>how is anodising of aluminium carried out?</p>, <p>state uses &amp; advantages of anodising of aluminium</p>, <p>how is purification of copper carried out?</p>, <p>state uses &amp; advantages of purification of copper</p> flashcards
H2 Chemistry 21 - Electrolytic cells

H2 Chemistry 21 - Electrolytic cells

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  • how to predict what substance gets liberated @ each electrode during electrolysis

    state ALL species present in electrolyte >

    which species reduced @ cathode, oxidised @ anode? >

    to determine substance discharged @ each electrode, 3 factors affect selective discharge of species;

    1. compare e nought values; > -ve gets oxidised, > +ve gets reduced

    2. [ion] affects reduction potential

    3. nature of electrode; reactive?

  • where do electrons flow in electrolysis?

    cathode(-ve) -> anode(+ve)

    not like galvanic cells where anode(-ve) -> cathode(+ve)

  • how to solve qualitative electrolysis?

    identify all species present >

    consider possible species for each electrode(metals only [O]); >1 species for electrode, compare e nought values to predict species discharged

    template:

    @ -ve cathode, ___ > easily [R] than ___ as e nought() is >+ve/<-ve than e nought()

    @ +ve anode, ___ > easily [O] than ___ as e nought() is >-ve/<+ve than e nought()

    always use full forward arrow

  • formulas to calculate amount of substance liberated

    total charge by 1 mol of e- = (6.02x1023) x (1.60x10-19)

    = 96500C

    total charge passed, Q = amount of e- passed in circuit x Faraday's constant

    Q = neF

    current(rate of flow of electric charge in s), I=Q/t

    total charge passed, Q = current x time; Q=It

    current in amps(A), time in seconds(t)

  • what is the relationship between Q=It=neF and amount of product formed?

    mass/volume of substance formed proportional to total charge Q=It

  • how is anodising of aluminium carried out?

    purpose: form stronger, thicker layer of aluminium oxide to improve corrosion resistance

    components in cell set up

    electrolyte: dilute H2SO4(aq)

    cathode: Pt/graphite electrode

    anode: Al electrode

    species present: H+, SO42-, H2O

    @ anode, H2O oxidised; 2H2O(l) -> O2(g) + 4H+ + 4e-

    O2(g) reacts w/ Al anode to form thick porous layer of oxide

    2Al(s) + 3/2O2(g) -> Al2O3(s)

    OVERALL anode eqn

    2Al(s) + 3H2O(l) -> Al2O3(s) + 6H+ + 6e-

    @ cathode, H+ reduced; 2H+ + e- -> H2(g)

    OVERALL eqn

    2Al(s) + 3H2O(l) -> Al2O3(s) + 3H2(g)

  • state uses & advantages of anodising of aluminium

    metal corrosion resistance increased

    porous surface of oxide layer can be dyed to diff colours

  • how is purification of copper carried out?

    purpose: extract pure Cu from manufactured product

    components in cell set up

    electrolyte: CuSO4(aq)

    cathode: pure Cu electrode

    anode: impure Cu electrode

    species present: Cu2+(aq), SO42-(aq), H2O(l), Cu&impurities

    anode: Cu(s) -> Cu2+(aq) + 2e- (impure Cu dissolves)

    cathode: Cu2+(aq) + 2e- -> Cu(s) (Cu deposited on pure Cu)

    blue soln does not fade during electrolysis

    impurities @ anode may not get oxidised & get collected as anode sludge,

    some may get oxidised but not reduced @ Cu cathode as e nought value too

    -ve wrt Cu2+

  • state uses & advantages of purification of copper

    used for electrical wiring as Cu has high electrical conductivity, tensile strength, corrosion resistance, etc.