NECO 2018 Chemistry Practical Answer – June/July Expo

NECO 2018 Chemistry Practical Answer – June/July Expo Lawrence Victor 5 of 5

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NECO Chemistry Practical Solution Questions and Answer - June/July 2018 Expo Runz


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(1a)
Tabulate:

Titrations |Rough|1st |2nd |3rd |
Final burette reading |18.00|15.60|17.40|20.50|
Initial burette reading |0.00 |0.00 |2.00 |5.00 |
volume of Acide used |18.00|15.60|15.40|15.50|

(1ai)
Average volume of Acid used
VA = (VA1 + VA2 + VA3)cm3/3
VA = (15.60+15.40+15.50)/3
VA = 46.50/3 
VA = 15.50cm3

(1aii)
2HCl(aq)+Na2CO3(aq)-->2NaCl(aq)+H2O(l)+CO2(g)

(1bi)
CA VA/CB VB =NA/NB
0.1moldm^-3 x 15.50cm3/CB x 25cm3 x 2/1
CB x 25cm3 x 2 = 0.1moldm^-3 x 15.50cm3 x 1
CB x 50 = 1.55
CB = 1.55/50 = 0.031moldm^-3

(1bii)
25cm^3---->0.031mole
1000cm^3---->x
x=1000*0.031/25=31/25
x=1.24moldm^-3

(1biii)
concentration in mold^-3 =Con glm^3 /molar mass
0.031moldm^-3=x/106
x=0.031*106
x=3.286gldm^3

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2a)

Tabulate

2ai)
OBSERVATION:

i)C dissolves in water

ii)formation of white precipitate

iii)White precipitate dissolves in itel

INFERENCE:

i)C is soluble in water

ii)CO3^-2,SO4^-2,SO3^2- suspected

iii)CO3^2-,SO3^2-, suspected

2bi)
OBERSVATION:

i)effervescence occurs with the evolution of a gas

ii)the solutions turns to pink

INFERENCE:
i)CO3^2-,SO3^2-, suspected

ii)CO3^2-,Confrimed

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3ai)
Zinc chloride reaction with HaOH form white gelatinous precipitate solution in excess HaOH.
Ammonium trioxocarbonate(iv) on reaction with HaoH evolves a gas which turns red litmus paper blue and lime water milky. Calcium trioxocarbonate(iv) on reaction with HaoH forms white powdery precipitate insoluble in excess HaOH.

3aii)
i)liquid substance--> crystallization
ii)Solid substance--> precipitation

3bi)
i)Evaporation takes place at all temperatures, while boiling occurs at a particular temperatur (at boiling point).
ii)Evaporation takes place from the surface, whereas the entire liquid boils.

3bii)
Carbon(iv)oxide does not support combustion

3ci)
molar solution is an aqueous solution that contains 1 mole (gram-molecular weight) of solute in 1 liter of the solution.

3cii)
Indicator

3ciii)
i)methyl orange 
ii)Phenolphthalein.

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