2021 NECO CHEMISTRY PRACTICAL EXPO – 9:00 – 12:00 PROMPT

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Updated: July 13, 2021 — 6:17 pm

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  1. NECO 2021 CHEMISTRY PRACTICAL ANSWERS
    (1a)
    Tabulate

    Volume of pipette used=25cm3.
    Indicator used= Methyl orange

    Under Titration, Rough, 1st, 2nd, 3rd,

    Final burette reading; |25.00| |23.40| |23.50| 23.60|

    Initial burette reading; |0.00| |0.00| |0.00| |0.00|

    Volume of A used; |25.00| |23.40| |23.50| |23.60|

    (1ai)
    Average volume of Acid used=23.40+23.50+23.60/3 =70.5/3=23.50cm3

    (1aii)
    This is because it is a reaction between a weak acid and strong base

    (1aiii)
    A funnel should be used while transferring the acid into the burette.

    (1bi)
    Conc of A in mol|dm³ =?
    Conc of A in g|dm³ = 12.75g|dm³
    Molar mass of A, NaHSO⁴ = 23+1+32+64
    =120g|dm³

    From.
    Conc(mol/dm³) = conc(g/dm³)/molar mass

    Conc =12.75/120
    Conc =0.106mol/dm³

    (1bii)
    Con of B in mol/dm³ =?
    Ca =0.106, Cb =? Va =23.50cm³, Vb =25.00cm³

    na=1 , nb=1
    From; CaVa/CbVb=na/nb
    Cb=CaVanb/Vbna
    Cb=0.106*23*50*1/25.00*1
    Cb=2.5/25
    Cb=0.1mol/dm³

    (1biii)
    Conc of B in g/dm³=?
    Molar mass of B , NaOH=23+16+1=40g/mol
    From; conc(g/dm³)=conc(mol/dm³)*molar mass
    =0.1*40
    =4.0g/dm³

    (1biv)
    Mass of salt formed =?
    Recall mole of NaHSO⁴=?
    From; mole =con(mol/dm³)*vol(cm³)/1000

    Mole=0.106*23.50/1000
    Mole=0.0025mol of NaHSO⁴

    By proportion 1mol of NaHSO⁴ produce 1mol of Na²SO⁴ 0.0025mol of NaHSO⁴ will produce X mol of Na²SO⁴ X=0.0025*1=0.0025mol of NaSO⁴
    Molar mass of Na²SO⁴=(23*2) + 32 + (16*4)
    =46+32+64
    =142g/mol

    Recall; mole =mole/molar mass
    Mass =mole * molar mass
    Mass =0.0025*142
    Mass =0.36g of Na²SO⁴
    ====================================

    (2a)
    TEST
    C + 5cm³ of distilled water

    OBSERVATION
    It dissolve completely

    INTERFERENCE
    C is a soluble salt

    (2bi)
    TEST
    Solution + NaOH + Heat

    OBSERVATION
    Effervescence occurs in which a colourless gas with pungent smell and turns red litmus paper to blue is given off.

    INFERENCES
    NH³ gas from NH⁴+ is present

    (2bii)
    TEST
    Stirring rod of HCL + gas given off

    OBSERVATION
    a gas which gives a pop sound is given off

    INFERENCES
    H² is present

    (2ci)
    TEST
    Solution C + drops of BaCL²

    OBSERVATION
    a white precipitate is formed

    INFERENCES
    CO²^-3, SO²^-4, SO²^-3, May be present.

    (2cii)
    TEST
    Solution in C(i) + dil HCL

    OBSERVATION
    the white precipitate dissolve is dil HCL and effervescence occurs in which a colourless and odourless gas which turns blue litmus red and lime water milky is given off

    INTERFERENCE
    CO² gas from CO²^3- confirmed
    ====================================

    (3a)
    (i)Ca²+
    (ii)Pb²+

    (3bi)
    concentrated acid can be defined as an acid formed when a large quantity of an acid dissolve in a small or little volume of water.

    (3bii)
    A strong acid is defined as a type of acid that ionize completely in a solution

    (3c)
    Activated charcoal is used as an adsorbent material

    (3d)
    (i)Reddish – Brown
    (ii) I – red, II – brown.
    ====================================

    Completed!. Promise Fulfilled.

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