WAEC (WASSCE) 2023 May/June CHEMISTRY (OBJ & ESSAY) QUESTIONS AND ANSWERS

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2023 WAEC CHEMISTRY OBJ;-ExamgrandComNg

1-10 ACADABBDAC
11-20 BCAABBCCBB
21-30 ACBABDACBB
31-40 ABBDAADCDD
41-50 BDCDDCDDCD

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CHEMISTRY QUESTION !!!!!  

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WAEC CHEMISTRY ANSWERS:-Examgrand!!!!!  

(1) 

1a)
Transition element can be defined as an element in which at least one of its simple ions or atoms has an incomplete inner shell of d-electrons. They are known as d-block elements. They are in three rows with ten elements in each row

(1b)
i – B
ii – C

(1c)
There is an increase in the first ionization energy accross the periodic table due to increase in the number of volume electrons leading to an increase in the screening effect and nuclear attraction between the nucleus and the outermost electrons.

(1d)
– Alkane eg Butane
– Alkene eg Ethene

(1e)
Alkanols are stronger base than water due to the presence of hydroxyl ions (OH-) in them.

(1f)
– Salt (Nacl)
– Limestone (CaCO3)
– Ammonia (NH3)
– Coke (C)

(1g)
This is also known as Cis-trans isomerism. It is a term which involves the spatial arrangement of atoms within the molecules

(1h)
This is because it has a high calorific value due to the combustible nature of the component gases

(1i)
Heat of combustion can be define as the amount of heat involved when 1 mole of substance burns in air or oxygen under standard conditions

(1j)
(i) Faraday’s second law of electrolysis states that when the same quantity of electricity is allowed to pass through different electrolytes, the number of moles of the ions deposited is inversely proportional to the charge.

(ii) Q=10920c
If = 96500C mol-¹
N= Q/nf
N= 10920/1×96500
N= 0.113 moles
:. mole= 0.113 moles

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(2) 

(b) 

(c) 

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(3) 

Or 

(c) 

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Number 4

a)

Step 1) Prepare a solution of calcium chloride: Dissolve calcium chloride (CaCl2) in water to create a calcium chloride solution. This step involves measuring the appropriate amount of calcium chloride and adding it to a container of distilled water while stirring until the compound is completely dissolved.

Step 2) Add a source of carbonate ions: Introduce a source of carbonate ions to the calcium chloride solution. This can be achieved by adding sodium carbonate (Na2CO3) or sodium bicarbonate (NaHCO3) to the solution. The carbonate ions from these compounds will react with the calcium ions in the solution, forming calcium carbonate.

Step 3)Precipitation of calcium carbonate: A white precipitate of calcium carbonate will form as a result of the reaction between the calcium ions and carbonate ions. The reaction can be written as follows:

Ca2+ (aq) + CO3^2- (aq) → CaCO3 (s)

The solid calcium carbonate will precipitate out of the solution.

Step 4) Filtration and washing: Use filtration to separate the solid calcium carbonate from the liquid solution. Set up a filter paper in a funnel and pour the mixture through it. The calcium carbonate will be retained on the filter paper while the liquid, containing any remaining calcium chloride and byproducts, passes through.

Step 5) Drying: After filtration, transfer the wet calcium carbonate onto a watch glass or a suitable container. Allow the solid to air dry or use gentle heat to remove any remaining moisture. The resulting dry solid is calcium trioxocarbonate (IV), commonly known as calcium carbonate.

4di. The observation that pure HNO3 turns yellowish brown when exposed to air is due to the decomposition of nitric acid and the formation of nitrogen dioxide (NO2) gas. Here’s a brief explanation of the observation:

Nitric acid (HNO3) is a strong oxidizing agent, and it readily undergoes a reaction known as disproportionation when exposed to air. In this reaction, nitric acid acts as both an oxidizing agent and a reducing agent, resulting in the formation of nitrogen dioxide gas (NO2), water (H2O), and other nitrogen oxides.

The reaction can be summarized as follows:

4 HNO3 + O2 -> 2 H2O + 4 NO2

When nitric acid is exposed to air, atmospheric oxygen (O2) reacts with the nitric acid molecules, causing them to decompose. As a result, nitrogen dioxide gas is released, which has a characteristic reddish-brown color. The presence of even trace amounts of nitrogen dioxide can cause the solution of nitric acid to appear yellowish brown in color.

4dii. The laboratory preparation of hydrogen trioxonitrate (V) acid, also known as nitric acid (HNO3), involves the reaction between sodium nitrate (NaNO3) and concentrated sulfuric acid (H2SO4). The balanced equation for this reaction is as follows:

2 NaNO3 + H2SO4 -> 2 HNO3 + Na2SO4

In this reaction, sodium nitrate (NaNO3) reacts with sulfuric acid (H2SO4) to produce nitric acid (HNO3) and sodium sulfate (Na2SO4) as a byproduct.

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(5) 

(c) 

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