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During a laboratory experiment, a student compared the reactivity of aluminium, sodium and lead with dilute hydrochloric acid. He added small pieces of each metal into separate test tube containing HCl and observed: • Aluminium caused the solution to heat up. • Sodium reacted vigorously with flames. • Lead produced Bubbles slowly. (a) Explain the reason for the rise in temperature when aluminium reacts with dilute HCl. (b) Give a reason why the reaction of sodium with dilute HCl is extremely vigorous. (c) State why the reaction of lead with dilute HCl is slow and produces only a few bubbles.
ANSWER: (a) The temperature rises because aluminium reaction with dilute HCl in an exothermic reaction, releasing heat along with hydrogen gas. (b) Sodium reacts extremely vigorously with HCl because it is highly reactive, producing hydrogen gas rapidly with heat that can ignite the gas and causingRead more
ANSWER: (a) The temperature rises because aluminium reaction with dilute HCl in an exothermic reaction, releasing heat along with hydrogen gas.
(b) Sodium reacts extremely vigorously with HCl because it is highly reactive, producing hydrogen gas rapidly with heat that can ignite the gas and causing a vigorous reaction.
(c) Lead reacts slowly with dilute HCl because it is less reactive, so hydrogen gas is released gradually, forming only a few bubbles.
See lessWrite chemical equation to show what happens when ethanol: (I) burns in oxygen/air. (II) is heated at 443 K in excess conc. sulphuric acid. (III) reacts with acidified potassium dichromate.
I. When ethanol burns in air or oxygen, it reacts vigorously and is completely oxidised to form carbon dioxide and water, releasing heat and light energy in the form of a flame. II. When ethanol is heated strongly with excess concentrated sulphuric acid, a water molecule is removed from each ethanolRead more
I. When ethanol burns in air or oxygen, it reacts vigorously and is completely oxidised to form carbon dioxide and water, releasing heat and light energy in the form of a flame.
II. When ethanol is heated strongly with excess concentrated sulphuric acid, a water molecule is removed from each ethanol molecule and ethene (an unsaturated hydrocarbon) is formed; this is called dehydration.
III. When ethanol is treated with acidified potassium dichromate, it undergoes oxidation: the alcohol is converted into ethanoic acid (acetic acid) while the oxidising agent is reduced.
See lessIs the CBSE 2026 date sheet released?
Yes, the CBSE 2026 tentative date sheet for Classes 10 and 12 has been released on the official CBSE website. It provides students, parents, and schools with a clear outline of the proposed examination schedule well in advance, helping them plan their studies systematically. However, it is importantRead more
Yes, the CBSE 2026 tentative date sheet for Classes 10 and 12 has been released on the official CBSE website. It provides students, parents, and schools with a clear outline of the proposed examination schedule well in advance, helping them plan their studies systematically. However, it is important to note that this is only a tentative timetable and may undergo changes before the final version is announced. Students are advised to regularly check the official website, for updates and follow the latest notifications to ensure proper preparation and time management for their board examinations.
The tentative CBSE 2026 board exams are scheduled to begin on 17 February 2026. They may extend all the way until 15 July 2026 (covering main, supplementary, and special exams)
See less“Excessive use of chemicals and pesticides in agriculture adversely affect the environment.’’ Justify this statement.
Excessive use of chemicals and pesticides in agriculture harms the environment because these substances contaminate soil, water, and air. They kill beneficial microorganisms and insects, reduce soil fertility, and enter the food chain, affecting animals and humans. Persistent chemicals accumulate inRead more
Excessive use of chemicals and pesticides in agriculture harms the environment because these substances contaminate soil, water, and air. They kill beneficial microorganisms and insects, reduce soil fertility, and enter the food chain, affecting animals and humans. Persistent chemicals accumulate in ecosystems, causing long-term damage. Overuse also leads to pesticide resistance in pests, forcing farmers to use stronger chemicals, further worsening environmental pollution and ecological imbalance.
See lessName the parts of hind-brain of the human brain. Which part of the hind-brain controls involuntary actions such as blood pressure and salivation?
The hind-brain of the human brain consists of the cerebellum, pons, and medulla oblongata. Among these, the medulla oblongata controls involuntary actions such as blood pressure, heart rate, salivation and breathing, ensuring vital bodily functions continue automatically without conscious effort. ItRead more
The hind-brain of the human brain consists of the cerebellum, pons, and medulla oblongata. Among these, the medulla oblongata controls involuntary actions such as blood pressure, heart rate, salivation and breathing, ensuring vital bodily functions continue automatically without conscious effort. It acts as a regulatory center for essential life processes, coordinating signals between the brain and spinal cord. The cerebellum mainly controls balance and coordination, while the pons assists in communication within the brain.
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