Waec 2017 CHEMISTRY Practical Questions And Answers



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    NOTE THAT ^ MEANS Raise to power.
    Draw Your Table As Usual And
    Input The Following:-
    Volume of pipette=25.00cm^3
    indicator used- Methyl orange colour change at
    end point-yellow to orange/purple
    Note Use Your School End Point.
    ==============
    3i)
    lime juice is acidic in nature and the colour of
    methyl orange in acidic medium is red
    3ii)
    Iron(iii)chloride will be reduced to iro(ii) with
    yellow deposit of sulphur
    3iii)
    The color of KM2O4 is decolorized because
    SO2(g) acts as a reducing agent.
    3iv)
    Addition of ethanoic acid to KCO3 results to
    the liberation of a colorless and odorless gas
    CO2 which turns lime water milky
    ===============
    2a)
    Tabulate
    Test
    (i)Fn + H2O, then filter
    Observation
    White residue and blue filtrate was observed
    Inference
    Fn is a mixture of soluble and insoluble salts
    Test
    (ii)Filtrate + NaOH(aq) in drops, then in
    excess
    Observation
    A blue gelatinous precipitate which is
    insoluble in excess NaOH(aq) was formed
    Inference
    Cu2 + present
    Test
    (iii)Filtrate + NH3(aq) in drops, then in excess
    Observation
    A pale blue gelatinous precipitate was formed.
    The precipitate dissolves or is soluble in
    excess NH3(aq) to give a deep blue solution
    Inference
    Cu2+ confirmed
    Test
    (iv)Filtrate + dil.HNO3 +AgNO3(aq)
    Observation
    No visible reaction White precipitate formed
    Inference
    Cl- present
    Test
    +NH3(aq) in excess
    Observation
    Precipitate dissolved in excess NH3(aq)
    Inference
    Cl- confirmed
    2bi)First portion of residue +NaOH(aq) in
    drops, then in excess
    Observation
    White powdery precipitate which is insoluble in
    excess NaOH(aq)
    Inference
    Ca2+ present
    Test
    2bii)Second portion of residue + dil.HCl
    Observation
    Effervescence/bubbles; colourless, odourless
    gas evolved.
    Gas turns lime water milky and turns damp
    blue litmus paper red.
    Inference
    Gas is CO2
    CO3^2- or HCO3- present
    ===============
    1)
    Tabulate
    Burette reading|Final burette reading(cm^3)|
    Initial burette reading (cm^3)| Volume of acid
    used(cm^3)|
    Rough- 24.10,0.00,24.10
    First- 23.80, 0.00, 23.80
    Second- 23.75, 0.00, 23.70
    Third- 23.75, 0.00, 23.75
    Average volume of A used = 23.80 + 23.70 +
    23.75cm^3/3
    =23.75cm^3
    1bi)
    CAVA/CcVc=2/1
    Cc=CAVA/2VC
    =0.100*23.75Moldm^-3/2*25.00
    =0.0475moldm^-3
    amount of A used = 0.100x
    VA/1000=0.100*23.75/1000 =0.00237
    2moles Of A = 1mole of C
    0.002375mol of A = 0.002375mol/2
    100cm^3 of C contain 0.00237*100mol/2*25
    =0
    1000cm3ofCcontained0.002375x1000mol
    2×25
    =0.0475mol
    concentration of C in moldm-3
    =0.0475moldm-3
    1bii)
    Molar mass of Bing mol-1:
    Molar mass of Na2CO3.yH2O=mass
    concentration of Bingdm-3
    molar concentration of Binmoldm-3
    =13.6gdm-3
    0.0475moldm-3
    =286gmol-1
    1biii)
    Molar mass of Na2CO3 =
    [(2×23)+12+(16×3)]=106gmol-1
    Mass of anhydrous Na2CO3=106×0.0475gdm-3
    =5.035gdm-3
    Mass of water=13.6-5.035gdm-3
    =8.565gdm-3
    Mass of Na2CO3 =Molar mass of Na2CO3
    Mass of water y×Molar mass of water
    5.035=106
    8.565 18y
    y =106×8.565
    5.035×18
    =10
    =====COMPLETED=====

    GOOD LUCK


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