Class 10 Science - ICSE-CHEMISTRY
Study of Compounds – Hydrogen Chloride
The chapter 'Study of Compounds – Hydrogen Chloride' explores the preparation, properties, and chemical behavior of hydrogen chloride gas and its aqueous solution, hydrochloric acid. For ICSE Class 10 Chemistry students, this chapter is crucial as it tests understanding of laboratory preparation methods using non-volatile acids, fountain experiments demonstrating extreme solubility and acidic nature, and key analytical reactions like precipitation of chlorides. Questions from this topic regularly feature in both Section A and Section B of the board exam, often involving identification of gases, balanced chemical equations, and observation-based questions.
Start Learning FreeKey Concepts
Laboratory Preparation of HCl
Hydrogen chloride gas is prepared by heating sodium chloride with concentrated sulphuric acid at a temperature below 200°C.
Drying of HCl Gas
HCl gas is dried exclusively using concentrated sulphuric acid because other drying agents like quicklime or phosphorus pentoxide react chemically with HCl.
Fountain Experiment
This classic experiment demonstrates the high solubility of hydrogen chloride gas in water and its acidic nature, creating a fountain of blue litmus solution turning red.
Action of Aqueous HCl on Metals and Salts
Dilute hydrochloric acid reacts with active metals to liberate hydrogen gas and with specific salts to form characteristic precipitates like silver chloride.
Important Formulas
Board Exam Info
In ICSE Chemistry (Science Paper 2), this chapter typically carries about 4 to 6 marks. Questions commonly appear as balanced chemical equations, identification of unknown substances based on observations, and reasoning questions such as why concentrated nitric acid is not used in the preparation of HCl gas.
Frequently Asked Questions
Why is concentrated sulphuric acid used in the lab preparation of HCl instead of concentrated nitric acid?
Concentrated sulphuric acid is non-volatile, whereas concentrated nitric acid is volatile and would distill over along with the hydrogen chloride gas.
Why can't quicklime (CaO) be used to dry hydrogen chloride gas?
Quicklime is basic in nature and reacts chemically with acidic hydrogen chloride gas to form calcium chloride and water.
Why does anhydrous hydrogen chloride not affect dry blue litmus paper?
Dry HCl gas does not contain hydrogen ions (H+). Ions are formed only in the presence of water, which is necessary to exhibit acidic properties.
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