Patterns of problems
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- Get the best out of this chapter by practicing the kind of problems asked in various exams
Preparation of Dihydrogen
There are various methods for preparing dihydrogen from metals and metal hydrides.
  1. Laboratory preparation of dihydrogen - It is usually prepared by the reaction of granulated zinc with dilute hydrochloric acid.
  2. Commercial production of dihydrogen - Electrolysis of acidified water using platinum electrodes gives hydrogen.
Patterns of questions related to this concept often include multiple choice questions where you have to choose the correct statement, questions where you have to identify the right percentages or reagents used in the preparation reactions of hydrogen.
How to approach
To answer questions from this pattern correctly, make sure you are thorough with the reaction equations. Focus closely on the reagents used, the percentages of reactants used, the sequence of steps in the preparation method, and so on.
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Structure of Hydrogen Peroxide
Hydrogen peroxide has a non-planar structure. The molecular dimensions in the gas phase and solid phase are different. In this pattern, you can expect theoretical questions related to the arrangement of atoms, the bond angles, the linearity-non-linearity of the molecule, etc.
How to approach
To be able to answer these questions, be thorough with the structure of hydrogen peroxide in gas phase and solid phase. Pay special attention to detail like the dihedral angle of the molecules in gas phase and in solid phase .
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Different types of Hydrides
Another common pattern of questions related to this chapter is about the different types of hydrides. You can expect matching-type questions where you have to match different compounds with the type of hydrides they are. You can also expect questions on the different properties of these hydrides and also reactions and equations associated with them.
How to approach
The different types of hydrides include:
  1. Ionic or saline hydrides
  2. Covalent or molecular hydrides
  3. Metallic or non-stoichiometric hydrides
Here are some of their features:
    • Hydrides of group 13 such as , , etc. exist in polymeric forms such as , Thus, they make up their deficiency.
    • Hydrides of group 14 such as , , , ,etc. have tetrahedral shape. They are electron precise compounds.
    • Hydrides of group 15 and group 17 such as , , , , etc. contain lone pairs of electrons. They are electron rich compounds.
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Preparation of Hydrogen Compounds
An important pattern of questions in this chapter is on the preparation of different hydrogen compounds. Questions can be expected where you have to choose the correct reagent for a particular preparation method, choose the correct reaction equation, identify the right product, and so on.
How to approach
There are different methods of preparation for hydrogen, water, heavy water, and hydrogen peroxide. When preparing for questions related to this pattern, focus on the reagents used for the reactions, the equations, and the limitations of the preparation methods. Also, you will have to remember how the different products are concentrated or refined.
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