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Neco 2019 Chemistry Practical Answers – Free
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(2i)
Observation;
Solution turns blue
Inference;
Copper salt suspected.
(2ii)
Observation;
Blue gelatinous precipitate
Insoluble in excess NaOH
Inference;
Cu²+ suspected
Cu²+ Confirmed
(2iii)
Observation;
Blue gelatinous precipitate
Soluble in excess NH³
Inference;
Cu2²+ Suspected
Cu²+ Confirmed
(2iv)
Observation;
White precipitate
Inference;
SO4²- Suspected
(2v)
Observation;
Precipitate insoluble in excess
Inference;
SO4²- confirmed
TAKE NOTE ON THIS NUMBER 1
Each school have their titre value or end point. In our solution, we used 20.40cm3.
So make sure you use ur school’s titre value. Ask your chemistry teacher. Some school got 24.50, 24.20, 22.10, 22.40, etc. Make sure your average titre value tallies with that of ur school’s. Anywhere you see 20.40 in my work, edit it and re-solve with ur school’s value.
This is very important.
Thanks.
(1)
The volume or pipette used 25.00cm³
In a tabular form
Titrations |rough |1st|2nd|3rd|
Final reading |21.00|41.30|20.40|40.90
Initial reading|0.00|21.00|0.00|20.40
Vol of A used |21.00|20.30|20.40|20.50
(1ai)
Average volume of A = 20.30+20.40+20.50/3
=61.2/3
=20.40cm³
(1aii)
H2X(aq) + 2NaOH(aq)–>Na2X(aq) + 2H2O(l)
(1bi)
Mass conc. of B = 1g/250cm³
= 1g/0.25dm³ = 4g/dm³
Using :
Molar conc. = mass conc./molar mass
= 4/(23+16+1) = 4/40 = 0.1mol/dm³
(1bii)
Using CAVA/CBVB = nA/nB
CA = CBVBnA/VAnB
CA = 0.1×25×1/20.4×2
Concentration of A = 0.06127mol/dm³
(1biii)
Molar mass of A = mass conc/molar conc
=4.85/0.6127
=79.15
≅ 79gmol
(1c)
(i)it might contain traces of impurities which must be removed before being weighed
(ii)it is hygroscopic which readily absorb moisture from atmosphere
(3ai)
phenolphthalein
(3aii)
(i) Pink
(ii) Colourless
(3aiii)
(i)To give a sharp change in colour at the end of the acid base reaction
(3aiv)
(i)the burette must be rinsed with the acid or allow it to drain after rinsing with distilled water
(ii)Air bubble must not be allowed in the burette
(3av)
Neutralization reaction
(3bi)
(i) Hofmann voltameter.
(ii) Kipp’s apparatus
(3bii)
Because silver nitrate is photosensitive (i.e.sensitive to light) Therefore,if the silver nitrate is left in sunlight or any bright light, it breaks down (hydrolyses) to give black/brown silver oxide and nitric acid.
See Previous Neco Chemistry Practical Answers Below
Tabulate
Titrations|Rough|first(1)|second(2)|third(3)
Final burette reading-|20.50|14.90|15.00|15.10|
initial burette reading- |0.00|0.00|0.00|0.00|
volume of Acide used- |20.5|14.90|15.00|15.10|
1ai)
average volume of Acid used
1st+2nd+3rd/3
14.90+15.00+15.10/3=45/3=15cm^3
1aii)
2HCL(aq)+Na2CO3(aq)—->2NaCl(aq)+H2O(aq)+CO2(aq)
1bi)
CA VA/CB VB =NA/NB
0.1moldm^-3*15cm^3/CB*25cm^3 *2/1
CB * 25cm^3*2=0.1moldm^-3*15cm^3*1
CB * 50=1.5
CB=1.5/50=0.03moldm^-3
1bii)
25cm^3—->0.03mole
1000cm^3—->x
x=1000*0.03/25=30/25
x=1.2moldm^-3
1biii)
concentration in mold^-3 =Con glm^3 /molar mass
0.03moldm^-3=x/106
x=0.03*106
x=3.18gldm^3
CLICK HERE FOR THE no.2 IMAGE
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
CLICK HERE FOR THE no.3 IMAGE
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.
COMPLETED
Past NECO Chemistry Practical Answers
1ai) Methyl Orange
Reason:- Titration of strong acid against base
1aii) Yellow
1aiii)Hydrochloricacid
1aiv)2HCL(aq)+ x2Co3 -> 2 x CLaq + H20(aq) + CO2(g)
1b) Molar mass of HcL = 1+35.5
=36.5gmol^-1
Con of A is moldm^-3 =
Con of A of gdm^3/molar mass in gdm^3
=7.30gdm^-3/36.5gmol^-1
=0.200moldm^-3
1bii)
using CAVA/CBVB = a/b
CA = 0.200mol/dm^3
VA = 26.20cm^3
Cb = ?
VB = 25.0cm^3
a = 2mols
b = 1mol
0.200mol/dm^3 x 26.2cm^3/Cb x 25.0cm^3
= 2mols/1mol
Cb = 0.200×26.20×1/25.0×1
Cb = 5.24/25.0mol/dm^3
Cb = 0.2096mol/dm^3
1biii)
Conc. of B in gdm-3/Conc. of B in mol/dm-3
=10.6gdm-3/0.148 gdm-3
=101.15g
=101gmol-1
2ai)
INFERENCE:
Sample X is a soluble salt
2aii)
OBSERVATION:
A gas is evolved. The gas turns red moist litmus blue.
It forms white fumed when NaOH solution was added was added
2bi)
REAGENTS: Adition of KSCN Solution
(Fe2+): Pale-colouration
(Fe3+) Blood red colouration
2bii)
REAGENT: Addition of NaOH solution in drop till excess
(Fe2+): Dirty green gelatineous precipitaye which is insolube in excess NaOH.
(Fe3+): Reddish brown gelatineous precipitate which is insolube in excess NaOH.
2biii)
REAGENT: Addition of K2Fe(CN) solution
(Fe2+): It forms a dark blue precipitate
(Fe3+): A deep red colouration
3b)
– Burrette
– Reshort Hand
– Solution/Acid
– Conical Flask
– white tile
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