2018/2019 Waec Chemistry Practical Questions And Answers

WAEC 2018 PRACTICALS

(1a)
Volume of pipette used=25.0cm^3
TABULATE
Reading: Rough|1st|2nd|3rd
Final reading: 16.00|15.40|17.20|15.30
Initial reading: 0.00|0.00 |2.00 |0.00
Vol of acid used: 16.00|15.40|15.20|15.30

 Average volume of A used = (VA1 + VA2 + VA3) cm³
VA = (15.40 + 15.20 + 15.30)/3cm³
VA = 45.90/3 = 15.30cm³.

B contains 4.80g/250cm³
Hence x8 = 1000cm³
X = 4.80 × 1000/250 = 4.80 × 4 = 19.2gdm³

(1bi)
Hence molar concentration of B in moldm3
Mass Conc(8dm³) = molar Conc × molar mass
Molar Conc of B = mass conc/molar mass = 19.2gdm³/127gmol
Cb = 0.151moldm3

(1bii)
Concentration of A in moldm-³, CA is given by CAVA/CBVB = na/nb
Where CA = ?
VA = 15.30cm³,
na = 1
CB = 1.51moldm-³, VB = 25.0cm³, nb = 5
CA × 15.30/0.151 × 250= 1/5
Therefore CA = 0.151×25×1/15.30×5 = 3.775/76.50 = 0.049moldm-³
Hence Conc. Of A in moldm-³ = 0.049moldm-³

(1biii)
No of moles of Fe²+ in the volume of B pipetted
n= cv/1000 =
0.151×25.0/1000 =
 3.775/1000
= 0.003775moles of Fe²+

3a)
I)Desiccator- use for preserving moisture sensitive items

ii)Volumetric flasks are used for precise dilutions and
preparation of standard solutions.

iii)Glass rod are used to mix chemicals and liquids for
laboratory purposes .

3ii)
i)Amphoteric is Al2O3

ii) Neutral oxide is H2O

3iii) Crystallization

3b.
1. hno3aq to cuco3 solid. a light blue solid,
precipitates is formed

2. acidified kmno4 to c2h4. c2h4 is oxidized to
ethane-1,2-
diol

3. iodine solution to a paste of unripe plantain. a
bluish-black color is produced with iodine