Verified Waec GCE 2018 Chemistry Practical Answers

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Verified Waec GCE 2018 Chemistry Practical Answers
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    WAEC GCE CHEMISTRY PRACTICAL



    PLEASE NOTE THAT
    tabulate means draw a table
    ^ means raise to power
    / means divide
    + means addition
    * means multiply
    ==============


    (1ai)
    Tabulate:
    Burette reading |1 |2 |3 |
    final reading |24.80|34.50|20.65|
    initial reading |0.00 |10.50|6.55 |
    vol of acid used|24.80|24.00|24.10|

    (1aii) Average volume of A used
    Va = 24.00 + 24.10/2
    = 24.05cm^3


    (1bi)
    Concentration of A in moldm^-3
    A contains 0.79g of KMnO4 per 250cm³ of solution.

    Hence since 250cm³ = 0.79g
    100cm³ = Xg
    X = 1000×0.79/250 = 3.16g

    Hence Conc in g/dm³ of A = 3.16gdm^-³
    But molar conc = mass conc(gdm^-³)/molar mass(g/mol)

    Hence molar Conc.Of A= 3.16gdm^-3/molar mass ofA
    But molar mass of A = KMnO4
    = 39 + 55 + 4(16) = 39 + 55 + 64
    = 158g/mol

    Hence Conc in moldm^-³ of A = 3.16gdm^-3/158g/mol
    = 0.020moldm^-3

    (1bii)
    To get concentration of B in moldm^-³, we use the relation
    CAVA/CBVB = na /nb
    Where,
    CA = 0.02moldm^-³
    VA = 24.05cm^-³
    na = 1
    CB = ?
    VB = 25.0cm³
    nb = 5
    0.02×24.05/CB×25 = 1/5
    CB = 5 × 0.02×24.05/25
    = 2.405/25
    =0.0962
    CB = 0.096moldm^-³


    ================

    2)
    A is ZnSO4(aq)
    B is NaOH(aq)
    C is Pb(NO3)2 (aq)
    D is HCL(aq)

    Reasons

    ROW 1
    it is used to distinguish Pb from Zn since both behave alike with NAPth
    It gives a white precipitate with Pb^2+ ions but not with Zn^2+. The first
    row obviously shows that. Also there actually no visible reaction whne Itcl (A) and NaOlt are mixed(C)

    Row 2
    when A and B mirces, the products Zncl2 and
    H2SO4 one soluble hence no visible reaction
    is scene Between B and D, a white precipitate is seen because PbaS04 insoluble
    Between B and C, Zn^2+ On yield a white gelatinous precipate with NaOlta

    =================

    (3ai)
    Sodium is stored under paraffin oil to prevent its oxidation by atmospheric gases

    (3aii)
    desiccator lid must be greased with a thin layer of grease, to ensure an airtight seal.

    (3aiii)
    Because it is hygroscopic

    (3bi)
    Add an acid eg HCL and this gives a neutralization reaction and the indicator react with the acids. Heat the solution to obtain the NaCL(s)

    (3bii)
    Dip a rod in aqueous Ammonia and dip in a beaker containing the acids, only HCl produces dense white fumes of ammonium chloride

    (3ci)
    (i)Beaker
    (ii)glass rod
    (iii)volumetric flask

    (3cii)
    On adding the dilute HCL to Na3SO3 a gas with a chocking smell is allow


    =========COMPLETED============



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