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NABTEB GCE Chemistry Practical Expo Answer – Nov/Dec 2017

 

NABTEB GCE 2017 Nov/Dec Chemistry Practical Answer and Solution to the questions. Verified expo answer

1a )
i ) burette
ii) pipette
iii ) conical flask
iv ) beaker

1bi )
i ) application of 2 to 3 drops of indicator to the base
ii) titration( rush) of acid into base sonutaneously and swirled ( shaked )

1bii)
weak acid vs strong base = phenophthalein

1ci )
molarity of B = mass concentration / molar mass = 2. 20/ 0. 25/ 40
molarity of B = 8.8 / 40
molarity of B = 0.220 moldm ^ -3

1cii )
CaVa / CbVb = Ca = CbVbna / Vanb = Ca = 0. 22* 25 * 1/ 24 .60 * 2= 5. 5/ 49. 2
Ca = 0 .11178
Ca = 0 .112 mold ^ -3

1ciii )
molar mass = mass concentration / molar concentration = 3. 90/ 0. 112
molar mass of H 2X = 35gmol ^ – 1
hence H 2X = 35 = 2 + X = 35
X = 35- 2
K = 33
R . A. Mx = 33 gmol ^ – 1

2ai )
the ethanedioic acid turns pink or red on adding methyl organe to it

2aii )
the hydrated form is efflorescence- when expsosed to air it effloresces and turns yellow due to atmospheric oxidation to basic iron ( iii ) teltraoxosulphate ( iv )

2aiii )
Pb ( No 3) ( aq ) +H 2SO 4( aq ) – — – -> PbSO 4( aq ) +2HNO 3
lead ( ii) tetraoxosulphate ( vi ) is formed which is insoluble in water

2aiv )
Zn( s ) + CUSO 4( aq ) — – — > ZnSO 4( aq ) + CH ( s )
copper metal is deposited as zinc displaced copper

2bi )
CaC 2( s ) + 2H 2O ( s ) – — – — > C 2H 2( g) + Ca ( OH ) 2 ( aq )

2bii)
the reaction is exothermic and hence it should be performed on a leap of sand inside the flask to prevent the flask from cracking

2biii )
Impurities – Phospine ( PH 2) hydrogen sulphide ( H 2S ) and ammonica ( NH3)
Reagent : Copper ( II ) tetraoxosulphate ( vi ) solution

2biv )
i ) because it is slightly less dense than air
ii) because it is unstable and may explode on compression to a liquid

2bv)
the reaction with sliver trioxonitrate( v) dissolved in alcohol may be used to distinguish alkenes from alkyness as no reaction in alkene . While terminal alkynes form a white precipitate

3ai )
i ) it is not used because it react with the gas as thus 2NH3( aq ) + H 2SO 4( aq ) — – — > ( NH4) 2SO 4( s )

3aii )
ammonia is very soluble in water at s .t . p due to readness with which forms hydrogen bond with water ( NH3. H 20)

3aiii )
this is to prevent trickling back of gas and mixture of gas with water formed during reaction

3b)
i ) by grinding to powder to increase surface area of contact
ii) by increasing the temperature of liquid in some cases or lower the temperature as the case may be

3ci )
FbC 03( s ) Heat – — – > Pbo ( s ) + Co 2( g)
Pb ( N 03) 2( s ) Heat – – -> pb( s ) + 2N 02 ( g) + 02( g)

3cii )
NH4Cl turns moist red litmus blue
NaCl Neutral to litmus paper
( No Reaction is observed )

3d)
y= FeSo 4- -> Fe ^ 2+ + So 4 ^ 2-
Anions: So 4^ 2 – , So ^ 3 – , S ^ 2-

3ei )
F = Wire Gauze
E= drying agent e ,g silical gel , calcium oxide, phosphorus ( v) oxide amnonia,fused calcium chloride

3eii )
it is used in keeping and drying solids in an atmosphere that is dry and free of dust
3eiii )
it is always greased in order to make it air tight and hence exclude atmospheric moisture.

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