2019 JAN/FEB WAEC GCE Chemistry Question and Answers

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👑 2019 WAEC GCE CHEMISTRY ANSWERS👑

100% VERIFIED CHEMISTRY OBJ ANSWERS

1-10 BDABADDCAA
11-20: DADCDBDBAC
21-30: BDADDBBCAD
31-40: AADDDBBCAB
41-50: CCBBAACBAD

100% VERIFIED CHEMISTRY THEORY ANSWERS

(1a)
4
2He has a stable electron configuration compared to 9 4Be because it has a completely filled valence electron

(1bi)
-After forming an ionic bond.
H becomes H+. It will have zero(0) electron
-After forming an ionic bond.
Li becomes Li. It will have two(2) electrons.

(1bii)
1H+ had one(1) electron while neutral on forming an ionic bond, it losses one(1) electron.
3Li had 3 electrons while neutral on forming an ionic bond, it looses one (1) electron.

(1c)
(i) Raw materials should be easily and cheaply obtainable.
(ii) Means of transport.

(1d)
(i) Low evolution of heat.
(ii) Low energy waste.

(1e)
No of moles of chlorine reacting = 21.3/71 = 0.3moles

From the equation, rate of Turpentine to chlorine is 1 : 8
.:.No of moles of Turpentine = 0.3/8 = 0.0375
Using no of moles = mass/molar mass

Mass of Turpentine = 0.0375×136
= 5.1g

(1f)
Cracking means breaking down or decomposition of a compound by the action of heat alone.

(1g)
(i) Stability
(ii) Size of atomic radii.

(h) Carbohydrates are naturally occurring organic compound containing carbon, hydrogen and oxygen with the hydrogen and oxygen present in the ratio of 2 : 1

(1i)
(i) A simple sugar is crystalline, starch is not.
(ii) A simple sugar is soluble in water, starch is not.

(1j)
(i) H2CO3/H2CO3 <=> 2H+ + CO3^2-
(ii) CH3COOH/CH3COOH <=> H+ + CH3COO^-

NOTE: <=> Means arrow forward and backward reaction sign ie arrow
<- ->

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

(2ai)
(i) Dilute acids and metal (soluble salt)
(ii) Alkali and acid (soluble salt)
(iii) Double decomposition

(2aii)
(i) Dilute acids and metal (soluble salt):
Zn(s) + 2HCl(aq)—->ZnCl(aq) + H2(aq)

(ii) Alkali and acid (soluble salt): NaOH(aq)+HNO3(aq)–> NaNO3(aq)+H2O(s)

(iii) Double decomposition: AgNO3(aq)+NaCl(aq)—>AgCl(s)+NaNO3(aq)

(2aiii)
(i) It used in manufacturing of glass
(ii) It used to standardized acid in the laboratory

(2b)
The impure copper is made the anode in an electrolytic cell containing pure copper cathodes and a copper(II)tetraoxosulphate (VI) solution as the electrolyte.

At the cathode
40H- —> 2H2O + O2 + 4e-

At the anode
Cu(s) —> Cu 2+ + 2e-

(2ci)
For sodium chloride = 39.0-36.6/39.0*100%
=2.7/39*100%
=0.0692*100%
=6.92%
for siliver nitrate = 952-297/952*100%
=655/952*100%
=68.8%
=========================

(3a)
(i)all elements are made up of small indivisible particles called atoms
(ii)atoms can neither be create nor destroyed
(iii)when atoms combine with other atoms they do so in simple ratios

(3aii)
The atoms of the same element can combine in more than one ratio to form two or more compound.

(3bi)
(i) margarine
(ii) soap
(iii) candles

(3bii)
CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH + 2H2(g) ———> CH3(CH2)6COOH

CH3(CH2)14COOC2H5 + NAOH——-> CH3(CH2)14COONa + C2H5OH
=================================

(4ai)
Hardness of water is a situation whereby water does not lather well with soap which is causes by dissolution of some salts like CaSO4 and MgSO4 in the water.

(4aiii)
(i) It causes furging of kettles and boilers.
(ii) It causes waste of soap and water.

(4bi) Ammonia NH3, OxygenO2

(4bii) Ammonia is poured over heated platinum rhodium catalyst at 700°c to produce NO and steam which then in the presence of excess air gives NO2. It is then sprayed with hot water to form HNO3

(4biii)
(I) S + HNO3 —> H2SO4(aq) + H2O(l) + 6NO2(aq)

(II) Aluminum does not react with conc. HNO3 due to the formation of protective coating of oxide on the metal.

(4c)
Al2O3 Aluminium oxide.

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