Chemistry 2009 Jamb Examination
Chemistry 2009 Jamb Examination
Question 21
Which of the following allotrope of carbon is a constituent of a lead pencil?
Graphite, a soft and slippery allotrope of carbon, is used in lead pencils because its layers can easily slide over each other. Unlike diamond, graphite is a good conductor and can leave marks on paper.
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Question 22
Which of the following metals will show the highest metallic character?
Calcium exhibits stronger metallic character than the others because metallic character increases down a group and decreases across a period. Being an alkaline earth metal, calcium readily loses electrons compared to zinc or copper.
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Question 23
Copper metal dissolves in concentrated trioxonitrate (V) acid with the resultant evolution of
When copper reacts with concentrated nitric acid, brown fumes of nitrogen dioxide $NO_{2}$ are released. This is a characteristic reaction where copper is oxidized while nitric acid is reduced to nitrogen oxides.
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Question 24
A catalyst increases the rate of a chemical reaction by providing a path that
A catalyst works by lowering the activation energy of a reaction, thereby allowing more particles to react at lower energy. It does not change temperature or concentration but improves reaction efficiency.
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Question 25
$CuO(s) + H_{2}(g) \leftrightarrow Cu(s) + H_{2}O(l)$
What is the effect of increasing the pressure on the equilibrium reaction above?
What is the effect of increasing the pressure on the equilibrium reaction above?
In this equilibrium, the number of gas molecules is the same on both sides. Increasing pressure has no effect because equilibrium shifts only when there is a difference in gaseous moles.
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Question 26
The equilibrium of an endothermic reaction which proceeds with an increase in volume can be shifted in the reverse direction by
For an endothermic reaction with volume increase, reducing the temperature favors the exothermic reverse reaction, and increasing pressure favors the side with fewer molecules, thus shifting equilibrium backward.
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Question 27
The oxidation of ammonia in excess air produces
In the Ostwald process, ammonia reacts with excess oxygen to form nitric oxide $NO$, which further oxidizes to $NO_{2}$. The first stable product directly formed is nitric oxide $NO$, making it correct.
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Question 28
Hydrogen sulphide gas can act as
Hydrogen sulphide is commonly used as a precipitating agent because it reacts with many metal ions in solution to form insoluble metal sulphides, making it useful in qualitative inorganic analysis.
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Question 29
Which of the following metals is purified commercially by electrolysis?
Copper is purified by electrolysis in the electrolytic refining process. Impure copper is used as the anode, and pure copper is deposited on the cathode, ensuring high-purity copper for industrial use.
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Question 30
What current will deposit 3.25g of zinc in 2hrs?
[$Zn = 65, F = 96500$ mol$^{-1}$]
[$Zn = 65, F = 96500$ mol$^{-1}$]
Using Faraday’s law: $n = \dfrac{Q}{zF}$. Moles of Zn = $\dfrac{3.25}{65} = 0.05$. Charge = $0.05 \times 2 \times 96500 = 9650$ C. Current $I = Q/t = 9650 / 7200 \approx 1.34$ A.
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|---|---|---|---|---|
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