Monday, 11 June 2018

NECO 2018 Chemistry Obj And Essay Answer – June/July Expo



NECO Chemistry Obj And Essay/Theory Solution Questions and Answer – JUNE/JULY 2018 Expo Runz.



    Chemistry OBJ:
    1DDDBCADBBC
    11DCDBDDCEDC
    21BBDEAAACCA
    31BCCBDACDCB
    41EAEBEECBAC
    51DADCCAABEB

    UPDATED: 1, 2, 3, 4 AND 6.

    Please Note: you are to answer 4 Questions only, in the Theory part
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    2a)
    A=1s^2,2s^2,2p^6,3s^2,3p^5
    B=1s^2,2s^2,2p^6,3s^2,3p^6,4s^2,3^9
    2aii)
    i)it is very mulleble
    ii)it is an excellent conductor of heat and electricity
    iii)it a red solidd with lustre
    2aiii)
    the oxidation state is -1


    2b)
    i)mecury
    ii)propan 1, 2diol
    iii)poly ethene
    2c)
    i)iron(iii)trioxocarbonate(iv)
    ii)Zinc sodium hydroxide
    iii)2Chloro but – 3 diene
    2d)
    i)Chalk- calcium carbonate
    ii) glass- silica sand
    iii) ceramics- kaolin/iron oxide/aluminum or sodium carbonate
    2ei)
    Faraday first law of electrolysis state that the mass of an element or substance (m) liberated at the electrode during electrolysis is directly proportional to the quantity of electricity (N) passing through it.
    Q2H2O+O2+4e
    from the oxidation half reaction of acidified water above it can be reduced that 4moles of electrons result to the formation of 1mole of oxygen
    ;4F=4*96,500C=386000
    I=2.5A
    t=1.5*60=90second
    Q=It=2.5*90=225C
    ;386000 require 22.4dm^3
    225c will require 22.4*22.5/386000
    =0.0131dm^3
    or 13.10cm^3



    1a)
    i)isotopy is a phenomenon whereby an atom of an element excite different mass number but have the same atomic number.
    ii)isomerism is existent of two or more compound (known as isomers) with the same molecular formulae but different molecular structure
    1aii)
    i)Deuterium
    ii)tritium’


    1bi)
    CLICK HERE FOR THE IMAGE
    Bottomed flask and set up the apparatus as shown. Add conc HCl gradual into the flask through the thistle funnel pass the gas produced through water and concentrated tetraoxosulphate (iv) and collect it by downward delivery.
    2KMnO4(aq)+16HCl—->2MaCl2(aq)+8H2O(s)+5Cl2(aq)
    1bii)
    i)it is use as a bleaching agent
    ii)it is use as disinfectant in the treatment of water
    iii)it is use as an oxidizing agent
    1ci)
    GIVEN
    P1=(745-13.5)mmHg =731.5mmHg
    T1=(16+273)k=289k
    P2=S.P=760mmHg
    T2=S.T=273k
    V1=40cm^3
    using the general gas equation
    P1V1/T1=P2V2/T2
    V2=731.5*40*273/760*289
    V2=36.4cm^3
    the volume of the gas at S.T.P is 36.4cm^3
    1cii)
    i)Nature of reactions
    ii)presence of a catalyst


    3ai)
    A homologous series is a family of organic compound which follows a regular structural pattern in which each successive member differ in its molecular formula. By-CH2-GROUP
    3aii)
    i)solubility
    ii)boiling points
    iii)densities
    3aiii)
    CLICK HERE FOR THE IMAGE


    3bi)
    catalyst are substance which alter the rate of a chemical reaction but not themselves used up in the process.
    3bii)
    i) they are proteinous in nature
    ii)they alter the rate of a chemical reaction
    iii)they are not use themselves up in the reaction
    3ci)
    The solution turn from blue to white as a magnesium displace copper from its salt
    3cii)
    Mg(aq)+CuSO4(aq)—–> MgSO4(aq)+ Cu(s)
    3di)
    Equation Reaction:
    2Na(s)+O2(q)—–>Na2O2(s)
    Number of moles of soduim =mass/molar mass =5.95/23=0.2587moles
    reactive ratio of sodium to its oxide is 2:1
    therefore number of moles of Na2O2=0.2587/2=0.129moles
    mass of oxide
    =0.129*[(23*2)+(16*2)]
    =0.129*78
    =10g
    3dii)
    i)dissolving an acid on hydride in water
    ii)combination of constituent element
    3diii)
    washing soda (NaCO3. 10H2O)


    4ai)
    From the collision theory the rate of chemical reactions depend on the frequency of effective collisions cones that the result in reaction between reactant particles
    4aii)
    cracking means breaking down or decomposition of a compound by the action of heat alone. while Reforming is the breaking down of a compound by the use of a catalyst
    4aiii)
    they are the most important processes for the commercial production of gasoline and diesel fuel


    4bi)
    i)Limestone: the limestone decomposes when heated to yield carbon(iv)oxide which is a major reactant
    Equation: CaCO3(s) –> CaO(s) + CO2(g)
    ii)Ammonia: The ammonia reacts with the carbon(iv)oxide ammonium hydrogen trioxocarbonate(iv)
    Equation: NH3(aq) + H2O(l) + CO2(g) –> NH4HCO3(aq)
    4bii)
    i)B belong to the class of compound called carbohydrates
    ii)C is ethanol [C2H5OH] , D is ethylethanoate [CH3COOC2H5]
    iii)Functional group is -OH
    iv)CH3COOH(aq)ethanoic acid + C2H5OH(aq)c —–>conc H2SO4(catalyst) —–> CH3COOC2H5(i) + H2O(i)
    4ci)
    CH(CH3)3,CH3CH2CH2CH3,CH3CH2CH2CH2OH/Increasing boiling points
    4cii)
    i)Bubbles formed at the bottom of liquid rise to the surface
    ii)temperature remain steady
    4ciii)
    i)Addition of sodium chloride crystals raises the boiling point of water
    ii)Reduction in atmospheric pressure lowers the boiling point of water
    4civ)
    i)N2O has oxidation state of +1 for Nitrogen
    ii)NO has oxidation state of +2 for Nitrogen
    iii)NO2 has Oxidation state of +4 For Nitrogen


    6ai)
    NH4^+(aq)+OH^-(aq)+HCl(aq)—> NH4Cl(aq)+H2O(i)
    6aii)
    the student got the choice of indicator wrong
    6aiii)
    phenolphthalein is used when a strong base is present. aqueaous ammonia is a weak base


    6b)
    i)gluclose and fructose
    ii)invertase
    iii)delivery tube
    iv)glucose
    6ci)
    white phosphorus and red phosphorus
    6cii)
    I. has no effect of red litmus paper
    II. changes damp blue litmus paper pink
    III. Reacts directly with alkali to yield a trioxocarbonate(iv)

    6di)
    GIVEN:
    mass of P= 9g
    molar mass of P =80g/mol
    : Number of mole of P presnt =mass/molar mass
    =9/80=0.1125moles
    solubility =0.1125/60*100=1.875mol/dm^3
    6dii)
    C2H5OH(aq) +H2SO4(aq)—-> C2H5HSO4(aq)+H2O(i)
    C2H5HSO4(aq)—->C2H4(aq)+H2SO4(aq) ethene
    6diii)
    Bromine Exists as liquid at room temperature because there is decrease in votality down the group of the halogens due to increasing strength of the van der waal’s force.
    =========================
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