ANSWER: Observations to justify chemical change: Effervescence (bubbling) is observed due to the evolution of hydrogen gas when zinc reacts with dilute sulphuric acid. Zinc granules gradually dissolve and a new substance, zinc sulphate solution, is formed. Hence, gas evolution and formation of a newRead more
ANSWER: Observations to justify chemical change:
Effervescence (bubbling) is observed due to the evolution of hydrogen gas when zinc reacts with dilute sulphuric acid.
Zinc granules gradually dissolve and a new substance, zinc sulphate solution, is formed.
Hence, gas evolution and formation of a new product confirm that a chemical change has taken place.
The compound X is ethanol, which is a good solvent. When ethanol reacts with sodium, it forms two products: Y, which is sodium ethoxide, and Z, which is hydrogen gas. The hydrogen gas produced is used in the hydrogenation of vegetable oils to convert them into vegetable ghee. The reaction can be repRead more
The compound X is ethanol, which is a good solvent. When ethanol reacts with sodium, it forms two products: Y, which is sodium ethoxide, and Z, which is hydrogen gas. The hydrogen gas produced is used in the hydrogenation of vegetable oils to convert them into vegetable ghee. The reaction can be represented as ethanol reacting with sodium to produce sodium ethoxide and hydrogen gas, showing the displacement of hydrogen from ethanol by the metal sodium.
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.
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.
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)
A student performs the following experiment in his school laboratory. List two observations to justify that in this experiment a chemical change has taken place.
ANSWER: Observations to justify chemical change: Effervescence (bubbling) is observed due to the evolution of hydrogen gas when zinc reacts with dilute sulphuric acid. Zinc granules gradually dissolve and a new substance, zinc sulphate solution, is formed. Hence, gas evolution and formation of a newRead more
ANSWER: Observations to justify chemical change:
Hence, gas evolution and formation of a new product confirm that a chemical change has taken place.
See lessA carbon compound X is a good solvent. On reaction with sodium, X forms two products Y and Z. Z is used to convert vegetable oil into vegetable ghee. Identify and name X, Y and Z. Also write the equation of reaction of X with sodium to justify your answer.
The compound X is ethanol, which is a good solvent. When ethanol reacts with sodium, it forms two products: Y, which is sodium ethoxide, and Z, which is hydrogen gas. The hydrogen gas produced is used in the hydrogenation of vegetable oils to convert them into vegetable ghee. The reaction can be repRead more
The compound X is ethanol, which is a good solvent. When ethanol reacts with sodium, it forms two products: Y, which is sodium ethoxide, and Z, which is hydrogen gas. The hydrogen gas produced is used in the hydrogenation of vegetable oils to convert them into vegetable ghee. The reaction can be represented as ethanol reacting with sodium to produce sodium ethoxide and hydrogen gas, showing the displacement of hydrogen from ethanol by the metal sodium.
See lessDuring 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