NECO GCE 2021 CHEMISTRY (ALTERNATIVE TO PRACTICAL) ANSWERS

COMPLETED

 

1ai)

-inconsidtent reading of the burette to the nearest whole number

-consistently reading burette to one decimal number

-arithmetic error

-lack of unit

-non concordant values

 

1aii)

Average Titre=24.55+22.60+22.50/3

=69.65cm³/3

=23.216cm³

 

1aiii)

Na²Co3+2HCL===>2Nacl+H20+Co2

 

1aiv)

Methyl Orange.

 

1av)

It’s a titration Between strong acid and Strong Base

 

1avi)

Pink

1bi)

CA=0.0050moldm-³,Na=2

CB=? VB=25cm³, Nb=1

VA=23.21cm³

 

CAVA= NA

===== ===

CBVB NB

 

0.050X23.21=2

CBX25.00 1

 

CBX2X25.00=0.0050X23.21X1

 

CB=1.1605/50 moldm³

CB=0.023moldm³

 

1bii)

Molar mass of Na2 Co3

2[Na]+ C+3 [O]

=2(23)+12+3+(16)

=46+12+48 gmol-1

Molar Mass of Na2Co3=106gmol-1

 

Concentration Of Na2Co3 in gdm-3

=CBx Molar Mass

=0.023×106 gdm-3

=2.438gdm-1

 

1biii)

1 Mole Of Co2=22.4cmd-3

Mole Ratio Of B(Na2Co3):Co2= 1:1

 

0.023mole=0.023mole

1mole of Co2=22.4dm³

 

0.023mole =22.4×0.023

=0.52dm³

 

 

1biv)

n=CV

n=0.05×23.21

n=1.16mole

 

=======================================

NO2a)

Observation| Inference

i) | Fe³+Present

ii) | Fe³+ Present

iii)brown

Solution ——-

Observed

 

iv)Red blood Cell ———- Observed.

 

2b)

i) |Co3²-,So3²- S²- may Present

 

ii) | Co3²-,So3² S²- may present

 

Iii)

KmnO4 Decolour Rised

 

 

 

2c)

i)Effervescence of greenish-yellow gas turns blue litmus red

ii)The Precipitate dissolved…

 

 

========================================

 

(3ai)

(i)To prevent sunlight Ray’s from affecting the solutions

 

(ii)To prevent the sucking back of water into the hot flask.

 

(iii) Because it is a component of glass

 

(iv)NaOH + CO² —> NaHCO³

 

(3bi)

(i)Heat iodine crystal

(ii)NH⁴Cl

 

(3bii)

(i)Stationary phase

(ii)Morning phase

 

*3aiv) 2NaOH + SiO3 —–> NaSiO3 + H2O*

 

 

 

 

 

COMPLETED

 

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