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2017 WAEC GCE CHEMISTRY PRACTICAL QUESTIONS AND ANSWERS - NOV/DEC EXPO NOW AVAILABLE . CLICK HERE TO SEE - solutionfans.com
   

  • 2017 WAEC GCE CHEMISTRY PRACTICAL QUESTIONS AND ANSWERS – NOV/DEC EXPO NOW AVAILABLE . CLICK HERE TO SEE - solutionfans.com
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    Chemistry Practical..

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    CHEMISTRY PRACTICAL

    Chemistry practical Answers..

    You are to answer all.
    (1ai)

    Burette Reading(cm^3)| 1   | 2    | 3 |

    Final Reading   |33.10|30.00|25.00|

    Initial Reading | 9.60|7.50 |2.40 |

    Volume of F used (cm^3)|23.50|22.50|22.60.
    (1aii)

    Average volume of F used

    =22.50 + 22.60 / 2

    =22.55cm^3
    (1bi)

    GIVEN:Molar Conc of Kmn04 =0.200mol/dm^2

    Volume of Kmn04 used =22.55cm^3

    Molar Conc of FeSo4. 7H2O=?

    Volume of FeSO4.7H2O=25cm^3

    Mole ratio of Kmn04 =1

    Mole ratio of FeSO4.7H2O=5
    Using,

    Molar Conc of KeSO4.7H2O x Volume(FeSo4.7H2O) =n(FeSO4.7H2O)/n(KmnO4)
    =molar Conc x 25 / 0.0200 x 22.55 = 5/1
    =Molar Conc.  x 25=0.0200 x 22.55 x 5

    =Molar Conc =0.0200 x 22.55 x 5 / 25
    =Molar Conc =0.0902mol/dm^3
    (1bii)

    Molar mass of FeSO4.7H2O

    =56+32+(4*16)+7(18)

    56+32+64+126 = 278g/mol

    Conc of FeSO4.7H2O in gdm-3 = 0.0900*278

    =25.02gdm-3
    (1biii)

    Mass of FeSO4.H2O = 33.60-25.02

    =8.58gdm-3

    Percentage of FeSO4.7H2O = (8.58/33.60) * 100

    = 25.54%

    (1ci)

    Hydrochloric acid(HCL) is a mild reducing agent and so it will consume a certain amount of Kmn04 during titration. This will give a slightly higher value of Kmn04 consumption than the actual amount needed by the analyte
    (1cii)

    As Kmn04 is a dark purple colour solution, it is not possible to take readings from the button of the meniscus on the burette as in usual. Hence, the top, of the meniscus is used(visibility consideration)
    (1ciii)

    No indicator is used because Kmn04 serves as an indicator
    ============================================

    (2a)

    TEST|OBSERVATION|INFERENCE
    (2ai)

    TEST: A+distilled water and stirred

    OBSERVATION: A disolved in water

    INFERENCE: A is soluble in salt
    (2aii)

    TEST: A(aq)+litmus paper

    OBSERVATION: Turns blue litmus paper red

    INFERENCE: A is an acidiic salt
    (2aiii)

    TEST: A(aq)+NaOH(aq)- in drops, then in excess

    OBSERVATION: -White gelatinous ppt formed.

    -Precipitate soluble/dissolved

    INFERENCE: Pb^2+ or Zn^2+ or Al^3+ present

    Pb^2+ or Zn^2+ or Al^3+ present
    (2aiv)

    TEST:A(aq)+NH3(aq)- in dropss,

    -then in excess

    OBSERVATION: -White gelatinous precipitate

    -Precipitate insoluble

    INFERENCE:   -Pb^2+ or Zn^2+ or Al^3+

    -Al^3+ present

    (2av)

    TEST: A(aq)+FeSO4(aq)+conc H2SO4

    OBSERVATION: Brown ring forms between the two solutions

    INFERENCE: NO3- confirmed
    (2bi)

    A is aluminium trioxonitrate(v)
    (2bii)

    Al(NO3)3
    (2c)

    TEST|OBSERVATION|INFERENCE
    (2ci)

    TEST: K+NaHCO3(aq)

    OBSERVATION: No visible reaction is observed

    INFERENCE: NaHCO3(aq) does not show result for alkanols(K)
    (2cii)

    TEST: K+benedict solution+heat

    OBSERVATION: There is no change in the colour of the benedicts solution

    INFERENCE: Benedicts solution is not an indicator for alkanols(K)
    (2ciii)

    TEST: K+KMnO4(aq)

    OBSERVATION: KMnO4(aq) solution changes from purple to colourless

    INFERENCE: Alkanol is being oxidized by KMnO4
    (2civ)

    TEST: K+CH3COOH+conc H2SO4

    OBSERVATION: pleasant fruity smell is observed

    INFERENCE: Esterification reaction has occured
    ================================================

    (3a)

    (i) Putsome distilled water in a beaker

    (ii) Measure 100cm^3 of 2.00mol/dm^3 of the stock solution by means of a burette and pour all the solution into the beaker containing the distilled water

    (iii) Stir the solution

    (iv) Transfer the solution into a 250cm^3 volumetric flask by means of a funnel

    (v) Ensure that all the solution in the volumetric flask has been transferred by thoroughly rinsing the inside of the beaker with distilled water

    (vi) Dilute the solution in the volumetric flask with distilled water until it reaches the 250cm^3 mark

    (vii) Shake the solution carefully
    (3b)

    (i) CH3COONa: It forms basic solution

    (ii) Al2(SO4)3: Acidic solution

    (iii) KNO3: Neutral solution
    (3c)

    Acidified potasium tetraoxomanganate(vii) KMnO4 was placed in the burette

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    Master Solution September 14, 2017 Categories: Education Guide 1246


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