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WAEC GCE 2023 - CHEMISTRY  ANSWER
WAEC GCE 2023 - CHEMISTRY  ANSWER

CHEMISTRY PRACTICAL


(1)





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(2)



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(3)
(3ai)
To convert an aqueous solution of copper sulfate (CuSOâ‚„) to an aqueous solution of zinc sulfate (ZnSOâ‚„), you can use a displacement reaction involving zinc.
CuSOâ‚„(aq) + Zn(s) ---> ZnSOâ‚„ (aq) + Cu(s)

In this reaction, zinc (Zn) displaces copper (Cu) from copper sulfate (CuSOâ‚„) because zinc is more reactive than copper. The zinc sulfate (ZnSOâ‚„) formed is soluble in water and remains in the solution.

(3aii)
CuSOâ‚„(aq) + Zn(s) ---> ZnSOâ‚„ (aq) + Cu(s)


(3b)
(i) A titrant is a solution of known concentration that is used to determine the concentration of another solution through a chemical reaction. It is added to the solution being analyzed during a titration.

(ii) Concordant titres refer to the multiple titration results that are within a narrow range of values, indicating that they are consistent and reliable. When the titration results are concordant, it means they are close to each other, and their average can be taken as an accurate measurement.




CHEMISTRY THEORY & OBJ

CHEMISTRY OBJ:
1-10: ACBBABACBA
11-20: ABBBADBBAB
21-30: CACBDCABCC
31-40: BDBDBBBADA
41-50: DAADBDBADD


(1)


(1d)
(i) Ensure that both copper(II) oxide and dilute trioxonitrate(V) acid used in the reaction are of high purity.
(ii) Ensure that the beakers and stirring rods used are clean and dry.



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

(2)




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(4ai)
Air is a mixture of gases, primarily composed of nitrogen, oxygen, carbon dioxide, and trace amounts of other gases.

(4aii)
Nitrogen

(4aiii)
A noble gas is an element from Group 18 of the periodic table, characterized by its stable and inert nature.

(4aiv)
(i) They are chemically inert
(ii) They have a full outer electron shell
(iii ) They exist as colorless, odorless gases at room temperature.

(4bi)
(PICK ANY TWO)
(i) Calcium chloride
(ii) Sodium sulfate
(iii) Potassium hydroxide
(iv) Anhydrous calcium sulfate

(4bii)
N2 + 3H2 ----> 2NH3

(4biii)
It is often done through upward displacement of air or downward delivery into a container.

(4biv)
Differences in the method of collection of gases depend on factors such as the gas's density, solubility, and reactivity with atmospheric components.

(4ci)
-Haematite undergoes reduction
-Coke acts as a reducing agent and provides heat.
-Limestone undergoes decomposition to form calcium oxide.

(4cii)
Cast iron is brittle and contains a higher percentage of carbon compared to wrought iron, which is malleable and has a lower carbon content.

(4ciii)
Conditions favoring the conversion of sulfur (IV) oxide to sulfur (VI) oxide include low temperature, high pressure, and the presence of a catalyst.

(4di)
Both diamond and graphite have high melting points due to the strong covalent bonds between carbon atoms in their structures. In diamond, each carbon atom forms four strong covalent bonds in a tetrahedral structure, while in graphite, carbon atoms are arranged in layers held together by weak van der Waals forces.

(4dii)
(I) Copper would react with silver trioxonitrate (V) but not with zinc trioxonitrate (V).

(II) The solution would change color, and silver metal would be observed as a solid precipitate.

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

(5a)
Soap is manufactured through a process called saponification. In this process, pellets of sodium hydroxide (NaOH) and vegetable oil are used as the main ingredients. First, the vegetable oil is heated, and then the heated vegetable oil is mixed with sodium hydroxide pellets. This mixture is stirred continuously until a thick, creamy consistency is achieved. This mixture is then left to cool and solidify into soap bars. The sodium hydroxide reacts with the fatty acids present in the vegetable oil, resulting in the formation of soap molecules.

(5bi)
The industrial preparation of oxygen from air involves a process called fractional distillation. Air is first compressed and cooled, causing it to liquefy. This liquefied air is then subjected to fractional distillation, a process that separates the different components of air based on their boiling points. Oxygen, which has a lower boiling point than nitrogen, is separated and collected as a pure gas.

(5bii)
(i) oxygen: Oxygen supports combustion and is necessary for a flame to burn.
(ii) Hydrogen: hydrogen is highly flammable and can readily ignite.

(5ci)
(i) Calcium hydroxide: It helps to neutralize any acidic components and improve the overall quality of the water.
(ii) Calcium: is an essential nutrient for human health and is important for the development and maintenance of strong bones and teeth.

(5cii)
(i) Natural sources
(ii) Fossil fuel extraction and combustion

(5ciii)
When sulfur reacts with iron, iron sulfide (FeS) is formed. This reaction can be represented by the equation:
Fe + S -> FeS

(5di)
The term hardness of water refers to the concentrationof dissolved minerals, particularly calcium and magnesium ions. Hard water can cause build-up and scaling in pipes and appliances, reduce the effectiveness of soaps and detergents, and can also affect the taste and odor of water.

(5dii)
2H2SO4 + 2NaCl –>> 2HCl + Na2SO4

(5diii)
Fe2O3 + 3CO –>> 2Fe + 3CO2



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