Is Hydrogen and its Compounds part of the EAPCET Chemistry syllabus?

Yes. Hydrogen and its Compounds is taught in Intermediate first year Chemistry, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.

How many Chemistry questions are there in EAPCET?

40 of the 160 questions in the Engineering paper are Chemistry, spread across 24 chapters.

What mistakes do students make in Hydrogen and its Compounds?

Writing Mg(HCO₃)₂ → MgCO₃ on boiling — magnesium precipitates as Mg(OH)₂ because it is less soluble than MgCO₃. Assuming boiling removes all hardness — chlorides and sulphates (permanent hardness) stay dissolved and need Calgon, washing soda or ion exchange. Drawing H₂O₂ as planar — it has an open-book, non-planar structure. Confusing normality with molarity in volume-strength questions — volume strength = 11.2 × M = 5.6 × N.

EAPCET Chemistry · Intermediate first year

Hydrogen and its Compounds

This chapter covers hydrogen’s isotopes, its preparation and properties, hydrides, water and its hardness, and hydrogen peroxide.

Subject: Chemistry
Taught in: Intermediate first year
Chemistry in the paper: 40 of 160 questions

Key formulas and results

Isotopes: protium, deuterium and tritium (radioactive)
Temporary hardness (bicarbonates) is removed by boiling; permanent hardness (chlorides, sulphates) is not
Hydrogen peroxide acts as both an oxidising and a reducing agent
Heavy water (D₂O) is used as a moderator in nuclear reactors
Hydrides are classified as ionic, covalent or metallic

What this chapter covers

Position and isotopes of hydrogen
Preparation and properties
Hydrides
Water and hardness of water
Heavy water
Hydrogen peroxide

How it is usually asked

Properties and structure of H₂O₂
Types of hardness and their removal
Classifying hydrides

Understanding Hydrogen and its Compounds

Hydrogen has the configuration 1s¹, so it resembles the alkali metals (it loses one electron) and the halogens (it gains one electron to reach a noble-gas configuration), which is why its position in the periodic table is debated. It has three isotopes — protium, deuterium and radioactive tritium — that differ only in neutrons, so they have the same chemistry but different rates of reaction. Hydrides are ionic with s-block metals, covalent with p-block elements, and metallic (often non-stoichiometric) with d- and f-block metals.

Hardness of water comes from dissolved Ca²⁺ and Mg²⁺. Temporary hardness, from bicarbonates, is removed by boiling or by Clark’s method (adding slaked lime), which precipitates CaCO₃ and Mg(OH)₂. Permanent hardness, from chlorides and sulphates, needs washing soda, Calgon (sodium hexametaphosphate) or ion-exchange resins. Heavy water, D₂O, is used as a moderator in nuclear reactors and to study reaction mechanisms.

Hydrogen peroxide has a non-planar, open-book structure and can act as both an oxidising and a reducing agent, because oxygen in it is in the −1 state, between 0 and −2. Its concentration is often expressed as volume strength: “10 volume” H₂O₂ means 1 L of solution gives 10 L of O₂ at STP on decomposition. EAPCET typically tests volume strength, hardness removal and the classification of hydrides.

Worked example

EAPCET-style question

What is the molarity of a “10 volume” hydrogen peroxide solution? (Take the molar volume at STP as 22.4 L.)

(1)0.45 M
(2)0.89 M
(3)1.79 M
(4)8.9 M

Solution

Decomposition: $\ce{2H2O2 -> 2H2O + O2}$ , so 2 mol $\ce{H2O2}$ give 1 mol (22.4 L) $\ce{O2}$ at STP.
10 volume means 1 L of solution releases 10 L of $\ce{O2}$ : moles of $\ce{O2} = \frac{10}{22.4} = 0.446\ \text{mol}$ .
Moles of $\ce{H2O2} = 2 \times 0.446 = 0.893\ \text{mol}$ in 1 L.
Molarity $\approx 0.89\ \text{M}$ ; equivalently, volume strength $= 11.2 \times$ molarity.
0.45 M is the moles of O₂, and 1.79 is the normality (n-factor 2), not the molarity.

Answer: 0.89 M

Common mistakes to avoid

Writing Mg(HCO₃)₂ → MgCO₃ on boiling — magnesium precipitates as Mg(OH)₂ because it is less soluble than MgCO₃.
Assuming boiling removes all hardness — chlorides and sulphates (permanent hardness) stay dissolved and need Calgon, washing soda or ion exchange.
Drawing H₂O₂ as planar — it has an open-book, non-planar structure.
Confusing normality with molarity in volume-strength questions — volume strength = 11.2 × M = 5.6 × N.

How to prepare it

A compact, factual chapter — reliable marks for one focused revision.

Once the formulas feel familiar, test them the way the exam does: practise Hydrogen and its Compounds questions chapter-wise, then attempt a full previous year paper to see whether it holds up under a 3-hour timer.

Related Chemistry chapters

See every chapter in the EAPCET Chemistry syllabus.

Practise Hydrogen and its Compounds chapter-wise

Chapter-wise quizzes show exactly which topics in this chapter you still get wrong — before a full paper does.

Frequently asked questions

Is Hydrogen and its Compounds part of the EAPCET Chemistry syllabus?: Yes. Hydrogen and its Compounds is taught in Intermediate first year Chemistry, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.
How should I prepare Hydrogen and its Compounds for EAPCET?: A compact, factual chapter — reliable marks for one focused revision.
How many Chemistry questions are there in EAPCET?: 40 of the 160 questions in the Engineering paper are Chemistry, spread across 24 chapters.
What mistakes do students make in Hydrogen and its Compounds?: Writing Mg(HCO₃)₂ → MgCO₃ on boiling — magnesium precipitates as Mg(OH)₂ because it is less soluble than MgCO₃. Assuming boiling removes all hardness — chlorides and sulphates (permanent hardness) stay dissolved and need Calgon, washing soda or ion exchange. Drawing H₂O₂ as planar — it has an open-book, non-planar structure. Confusing normality with molarity in volume-strength questions — volume strength = 11.2 × M = 5.6 × N.