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Wednesday, June 12, 2019

NECO 2018/2019 CHEMISTRY PRACTICAL QUESTION AND ANSWERS RUNZ JUNE/JULY

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Wednesday 6th June 2018
Practical – Chemistry – 10:00am – 12:00noon

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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

(2a)
Tabulate

(2ai)
OBSERVATION: C dissolves in water
INFERENCE: C is a soluble salt

(2aii)
OBSERVATION: White precipitate formed
INFERENCE: CO3²-, SO3²-, SO4²- suspected

(2aiii)
OBSERVATION: White ppt dissolves in excess of dil HCl
INFERENCE: CO3²- , SO3²- suspected

(2bi)
OBERSVATION: Effervescence occurs with the evolution of a gas
INFERENCE: CO3²- present

(2bii)
OBERSVATION: Solutions turns to pink
INFERENCE: CO3²- Confirmed

(3ai) 
Zinc Chloride(ZnCl2) solution reacts with NaOH(aq) to form white ppt in drops. The precipitate dissolves in excess of NaOH. 

Sodium hydroxide reacts with ammoniumtrioxocarbonate(iv) to form a solution which turns red litmus paper blue. 

Calcium trioxonitrate(v) Ca(NO3)2 on reaction with sodium hydroxide forms a white powder precipitate insoluble in excess NaOH(aq)

(3aii) 
I. Liquid substances -  Boiling point of the substances. 
II. Solid substances - The melting point of the substance. 

(3bi) 
(i) Evaporation takes place at almost all temperatures, while Boiling takes place at a specific temperature. 
(ii) Only the surface of a liquid is involved in evaporation while the entire mass of the liquid is involved in boiling. 

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

(3ci)
A molar solution is an aqueous solution that contains one mole of solute in 1000cm³ of the solution. 

(3cii)
Indicator. 

(3ciii) 
(i) Methyl orange

(ii) Phenolphthalein


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