Verified Waec GCE 2018 Chemistry Obj & Theory Answers

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Verified Waec GCE 2018 Chemistry Obj & Theory Answers
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    WAEC GCE CHEMISTRY

    CHEMISTRY OBJ:
    1-10: CCDBACBABA
    11-20: BDDDCDBAAA
    21-30: CAADCCCAAB
    31-40: CBBCABCDBC
    41-50: BACCAABACC
    Completed

    CHEMISTRY OBJ..
    trace your answer from the option.
    ==========

    1. Yard
    2 freezing point
    3.
    4. Stronger intermolecular forces
    5. Avoaadros number
    6. 64 og
    7 electron sharing between metals and
    8. HF
    9. dative
    10. Cations are smaller than their atoms
    11 Solubility
    12 I2
    13. 20
    14.
    15 periodic table
    16 speed of forward reaction
    17 2-bromo
    18. 4fe + 30 - - - > 2Fe
    19 Reduced and its oxidation number increase
    20 Ca(oH)
    21. 1.2gm
    22. CH3 CooNa
    23. activation energy
    24. Plastic
    25. Exhoost of vehicles
    26
    27
    28 sulphur (iv) oxide
    29
    30 copper oxide
    31 Naheptone
    32. 2,2, 4 trimethy/pebtane

    42. Ionic radius
    43. Protein
    44. Molecule
    45. Number of valence electron
    46
    47 saturated
    48. strong electofovalent bond between ions
    49. 5.6dm
    50.Endothermic
    ======================




    CHEMISTRY THEORY ANSWERS

    (1a)
    Gas > liquid > Solid

    (1aii)
    Solid > liquid > gas

    (1bi)
    PH>7

    (1bii)
    PH>7

    (1ci)
    (I) Magnesium from 0 to +2
    (II) Hydrogen changes from 1 to 0

    (1cii)
    I ---> Magnesium is oxidized
    II ---> Hyfrogen is reduced

    (1ciii)
    HCL

    (1di)
    (i) Boiling occurs throughout the entire volume while evaporation occurs at the surface
    (ii)It involves the formation of bubbles while evaporation does not form bubbles

    (1dii)
    It decreases the boiling point as the boiling point of water is proportional to the magnitude of atmosphere pressure.

    (1e)
    It dictates the rate of reaction and also optimize the amount of product formed.

    (1f)
    C3H7CooH ---> Butanoic acid
    (CH3)3COH ---> Butan-1-ol

    (1g)
    Functional groups are responsible for their different chemical behavior or properties so that organic compounds with smaller functional group would behave similarly.

    (1h)
    Solids in liquid:
    (i) It depends on the nature of temperature changes or exothermic or endothermic as affect by the temperature of the liquid.
    (ii) The surface area of solid is lesser, they dissolves less as compound to gases in the same volume.
    (iii) Pressure does not affect the solubility of the solids

    Gas in liquid:
    (i) It depends on the average kinetic energy as affect by temperature of the liquid.
    (ii) The surface area of gases are higher so they dissolve more in a given volume of water.
    (iii) The solubility of gases is a direct consequences of pressure changes due to the partial pressure of the gas molecules.

    (1i)
    3F2 + 3H2O -> 6HF + O3

    (1j)
    Basicity of an acid is the number of replaceable hydrogen ions in the acid.
    =========================





    2ai)
    carbon - 0.48/12 , 0.04/0.04 , 1
    hydrogen - 0.08/1 , 0.08/0.04 , 2
    chlorine - 1.42/35.5 0.04/0.04 , 1
    Therefore CH2CL
    The electrical formular = CH2CL
    2aii)
    The molar mass of the compound is 99
    Hence (CH2CL)n = 99
    (12 + 2C1) + 35.5)n = 99
    12 + 2 + 35.5
    (495)n = 99
    Therefore n = 2
    Hence the molar formula = (CH2CL)2
    C2H4CL2
    2bi)
    i)it i solid at room temperature
    ii)it does not contain molecule
    iii)they do not dissolve in non-polar solvent

    2ci) CLICK HERE FOR THE IMAGE

    2cii)
    i)Eq1- actuation energy for in catalyzed reaction
    ii)Eq2 - actuation energy for catalyzed reaction

    2di)
    Paraffin wax
    2dii)
    To obtain the fraction the crude oil must undergo fraction distillation. In this process the crude oil is separated into different portion and the paraffin's wax district in the temperature range of 35°c to 500°c
    2diii)
    i)ethene
    ii)propane
    2div)
    They can be obtained from the cracking of crude oil. Cracking which is the breaking down of the crude oil into smaller components through the action of heat

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

    4ai) addition of chlorine to the
    Water To Kill germs and organic substances

    ii) Addition of slake line me to
    remove hardness in water

    iii) addition of alum to coagulate and participate the impurities

    iv) passage of water through the activated carbon i.e animal charcoal go remove color and odour from water
    V) passage of water through the filter sand bed to remove the precipated impurities

    Vi) finally, storage of Water
    the tank for onward Supply to the tenk.
    (4bi)
    i) Iron impurity
    ii) mud or Sand.
    ======================

    5ai)
    i)CO
    ii)CO2
    5aii)
    It is because there is increasing surface area of the broken coal than in the lumps of coal
    5aiii)
    CH4
    5aiv)
    Coke
    5bi)
    SO2
    5bii)
    MnO2
    5aiii)
    Na2O
    5aiv)
    Al2O3
    5av)
    NO2
    5ci)
    Cl2+FeCl----->FeCl3

    5cii)
    Radox reaction
    5civ)
    Reason: the oxidation number of iron increases from +2 to +3 oxidation, and the oxidation number of chlorine decrease from 0 to - 1
    5di)
    A- delivery tube
    B- quicklime 
    5dii)
    2NH2 Cl2(s)+ Can(OH)2(s)----->CaCl2(s)+2H2O(s)+2NH3(g)
    5diii)
    Ammonia
    5div)
    To prevent sucking back
    5dv)
    To absorb or dry the ammonia gas
    5e)
    Bitumen
    =====================

    (3ai)
    When potassium chloride dissolves in water, the bond in the solid particle breaks thereby increasing the kinetic energy of the particle to move. Particles in solid state have restricted or static movement unlike those in the form of ions or gases.

    (3aii)
    It is endothermic because it involves bond breaking and heat is absorbed in the process.

    (3bi)
    An underground iron pipe is less likely to erode if it is bonded at intervals with magnesium rod because the magnesium is more electro positive thereby absorbing the water or little oxynegn it is exposed to. In addition, corrosion is influenced by the presence of oxygen and water, therefore underground iron pipe will be exposed to little oxygen and water.

    (3bii)
    (i) First, conversion of Iron II to Iron III
    Fe²+(aq) + e- --->Fe³+(aq)

    (ii) Exposure to oxygen and water vapour.
    4Fe(s) + 3O2(g) + xH2O(l) --> 2Fe2O3 xH2O
    Iron rod Iron rust



    (3biii)
    The iron in water will be oxidized since there is dissolved oxygen and atmospheric oxygen & a brown deposit of Iron occurred.

    (3ci)
    A spontaneous reaction is a reaction that can exist freely on its own without any external factor. A reaction is said to be spontaneous if ΔG, is the Gribb's free energy is negative. ΔG = -ve
    An example is rusting of Iron.

    (3cii)
    (i) When Gribb's free energy is negative.
    (ii) When Entropy ie Δs must be positive as the total entropy must increase.

    (3Ciii)
    This is because sodium is more electropositive than calcium. Also the heat evolved in the reaction with sodium is far greater than the heat of solution released with calcium and water at the same temperature.

    (3civ)
    2Na(s) + 2H2O(l) ---> 2NaOH(aq) + H2(g)
    Ca(s) + 2H2O(l) ---> Ca(OH)2 + H2(g)

    (3d)
    Mass of lead (ii) trioxocarbonate iv
    PbCO3
    = 207 + 12 + 3(16)
    207 + 12 + 48 = 267g
    1mole of PbCO3 contain 1 mole of Pb
    267g of PbCO3 = 207g of Pb
    Xg of PbCO3 = 35.0g of P
    X = 267×35/207 = 45.1g
    =45.1g of PbCO3

    (3e)
    (i) Covalent bond
    (ii) Ionic bond





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