Class 8 Science - ICSE-CHEMISTRY
Hydrogen
The chapter 'Hydrogen' in Class 8 ICSE Chemistry explores the lightest and most abundant element in the universe. Students learn about the occurrence of hydrogen, its laboratory preparation using metals and acids, and its physical and chemical properties. The chapter covers the crucial concept of reduction, where hydrogen acts as a reducing agent by removing oxygen from metal oxides. Water is also studied as an oxide of hydrogen. Understanding these concepts is vital for board exams, as questions frequently test preparation methods, balanced chemical equations, and the identification of gases through simple tests like the pop sound.
Start Learning FreeKey Concepts
Occurrence of Hydrogen
Hydrogen exists in a free state in volcanic gases and outer space, and in a combined state in water, acids, and organic compounds on Earth.
Laboratory Preparation
Hydrogen is prepared in the lab by the action of dilute hydrochloric acid or dilute sulphuric acid on active metals like zinc.
Physical Properties
Hydrogen is a colorless, odorless, tasteless, highly combustible gas that is lighter than air and insoluble in water.
Chemical Properties
Hydrogen burns with a pale blue flame to form water and reacts with non-metals like oxygen and chlorine under specific conditions.
Reducing Agent
Hydrogen removes oxygen from heated metal oxides, such as copper oxide, reducing them to pure metals while getting oxidized to water.
Important Formulas
Board Exam Info
In ICSE Class 8 Chemistry, this chapter typically carries around 5 to 8 marks. Common question types include balancing chemical equations for laboratory preparation, explaining the reducing property of hydrogen with equations, and identifying gases based on their physical tests.
Frequently Asked Questions
Why is concentrated nitric acid not used in the preparation of hydrogen?
Concentrated nitric acid is a strong oxidizing agent. Instead of releasing hydrogen gas, it oxidizes the hydrogen to form water and gets reduced to nitrogen oxides.
How can you test for hydrogen gas in the laboratory?
When a burning splinter is brought near the mouth of the test tube containing hydrogen gas, it burns with a pop sound.
Why is hydrogen collected by the downward displacement of water?
Hydrogen is insoluble in water and much lighter than air, making downward displacement of water the safest method for collection.
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