Class X Chemistry: Definitive University Study Guide (Bhutan Science Curriculum)

PREFACE AND CURRICULUM OVERVIEW

• Origin: Designed and written in accordance with the Science Curriculum Framework prepared by the Royal Education Council (REC), Ministry of Education, Bhutan.

• Reform Goals: Part of a major reform in the science curriculum starting from 2013, focusing on a spiral relationship in content flow across key stages to maximize learning in higher classes.

• Textbook Features:

  • Intended learning objectives for each main topic.

  • Self-evaluation questions following each topic.

  • Practical and theoretical activities to explain abstract concepts.

  • Summary for each chapter for time-efficient revision.

  • Chapter-end exercises, specimen question papers, and a glossary.

  • Introduction of topics using cartoon concepts to increase interest and interactivity.

• Pedagogical Approach: Blended with cooperative learning structures and transformative pedagogy to engage all students.

• Subject Importance: Class X Chemistry is considered a foundational tool for students pursuing future studies in the science stream.

ASSESSMENT IN CHEMISTRY

• Definition: A process of measuring student achievement in terms of knowledge, skills, and attitude. It must be accurate, objective, and valid.

• Purpose:

  • To inform and guide teaching/learning.

  • To help students set personal learning goals.

  • To assign report card grades and summary info for stakeholders.

  • To motivate and build confidence in learners.

• Domains of Assessment:

  • Scientific Knowledge (SK): Understanding of gas laws, mole concept, metallurgy, halogens, transition elements, energetics, rate of reactions, and alcohols.

  • Working Scientifically (WS): Nature of science, logical/abstract thinking, technological relationships, and communication of ideas (including ICT).

  • Scientific Values and Attitudes (SV): Ethical, social, industrial, and environmental implications of science.

• Assessment Types:

  • Continuous Formative Assessment (CFA): Daily, non-graded diagnostics to identify learning needs and provide feedback.

  • Continuous Summative Assessment (CSA): Continuous graded performance measurement to evaluate effectiveness and improve learning.

  • Summative Assessment (SA): Term-end examinations covering all three domains (Bloom's Taxonomy).

• Assessment Matrix Weightages:

  • Term 1 (T1): $30\%$, Term 2 (T2): $50\%$

  • Project Work: $5\%$

  • Practical Work: $5\%$

  • Class tests and homework: $10\%$

CHAPTER 1: GAS LAWS

• General Properties of Gases:

  • Molecules are in constant random motion.

  • Large intermolecular distance with weak forces.

  • Physical properties described by three variables: Temperature ($T$), Pressure ($P$), and Volume ($V$).

• Kinetic Molecular Theory (KMT):

  • Gas particles are in continuous, rapid, random motion.

  • Collisions between particles and container walls are perfectly elastic.

  • The average kinetic energy is directly proportional to the absolute temperature ($K \propto T$).

• Standard Units:

  • Temperature: Degrees Celsius ($^{\circ}C$) or Kelvin ($K$). $T(K) = t(^{\circ}C) + 273$.

  • Pressure: $1\text{ atm} = 760\text{ mm Hg} = 76\text{ cm Hg} = 101.325\text{ kPa}$. SI unit is Pascal ($Pa$).

  • Volume: $1\text{ Litre} = 1000\text{ mL} = 1000\text{ cm}^3 = 1\text{ dm}^3$. SI unit is $m^3$.

• Boyle’s Law (Pressure-Volume Relationship):

  • Statement: At constant temperature ($T$), the volume ($V$) of a sample of gas is inversely proportional to its pressure ($P$).

  • Formula: $PV = k$ or $P<em>{1}V</em>{1} = P<em>{2}V</em>{2}$.

• Charles’ Law (Volume-Temperature Relationship):

  • Statement: At constant pressure ($P$), the volume ($V$) of a fixed mass of gas is directly proportional to its absolute temperature ($T$).

  • Formula: $\frac{V}{T} = k$ or $\frac{V<em>{1}}{T</em>{1}} = \frac{V<em>{2}}{T</em>{2}}$.

  • Absolute Zero: The theoretical temperature at which volume becomes zero ($-273.15^{\circ}C$ or $0 K$).

• Avogadro’s Law:

  • Statement: Equal volumes of all gases under similar conditions of temperature and pressure contain equal numbers of molecules.

  • Standard Molar Volume: One mole of an ideal gas occupies $22.4\text{ Litres}$ at STP ($0^{\circ}C$ and $1\text{ atm}$).

• Combined Gas Law:

  • Formula: $\frac{P<em>{1}V</em>{1}}{T<em>{1}} = \frac{P</em>{2}V<em>{2}}{T</em>{2}}$.

• Ideal Gas Equation:

  • Formula: $PV = nRT$, where $R$ is the universal gas constant ($0.0821\text{ L atm K}^{-1} \text{ mol}^{-1}$).

• Dalton’s Law of Partial Pressures:

  • Statement: The total pressure ($P_{total}$) exerted by a mixture of non-reacting gases is equal to the sum of the partial pressures of the constituent gases.

  • Formula: $P<em>{total} = P</em>{1} + P<em>{2} + P</em>{3} + \dots + P_{n}$.

CHAPTER 2: THE MOLE CONCEPT AND STOICHIOMETRY

• Relative Atomic Mass ($A_{r}$):

  • Average mass of an atom of an element relative to $\frac{1}{12}$ of the mass of a Carbon-12 atom.

• Relative Molecular Mass ($M_{r}$):

  • The sum of the relative atomic masses of all atoms present in a molecule.

• The Mole:

  • An amount of substance containing $6.023 \times 10^{23}$ particles (Avogadro's Number, $N_{A}$).

  • $n = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}$.

• Empirical and Molecular Formulas:

  • Empirical: Simplest whole-number ratio (e.g., $CH_{2}$ for glucose).

  • Molecular: Actual number of atoms (e.g., $C<em>{6}H</em>{12}O_{6}$ for glucose).

  • $\text{Molecular Formula} = n \times (\text{Empirical Formula})$.

• Percentage Composition:

  • $\frac{\text{Total mass of element in compound}}{\text{Molar mass of compound}} \times 100\%$.

CHAPTER 3: METALLURGY

• Key Terms:

  • Mineral: Natural inorganic substance found in the earth's crust.

  • Ore: A mineral from which a metal can be extracted economically.

  • Flux: A chemical used to remove impurities (e.g., $CaO$ or $SiO_{2}$).

  • Slag: The waste product formed by flux reacting with gangue ($\text{Flux} + \text{Gangue} = \text{Slag}$).

• Concentration Methods:

  • Gravity Separation: Based on difference in density.

  • Magnetic Separation: Used if ore or impurities are magnetic (e.g., Magnetite).

  • Froth Floatation: Specifically for sulfide ores using pine oil and water.

• Chemical Extraction:

  • Calcination: Heating ore in absence of air (removes moisture/volatile matter).

  • Roasting: Heating sulfide ores in excess air to convert them to oxides.

• Alloys:

  • Stainless Steel: Iron + Chromium + Nickel.

  • Brass: Copper + Zinc.

  • Bronze: Copper + Tin.

CHAPTER 4: HALOGENS (GROUP 17)

• Physical Properties:

  • Fluorine ($F_{2}$): Pale yellow gas.

  • Chlorine ($Cl_{2}$): Greenish-yellow gas.

  • Bromine ($Br_{2}$): Reddish-brown liquid.

  • Iodine ($I_{2}$): Dark violet solid.

• Chemical Reactivity:

  • Reactivity decreases down the group (F > Cl > Br > I).

  • All halogens form halide ions ($X^{-}$) by gaining one electron.

  • Oxidizing Nature: Halogens are strong oxidizing agents.

CHAPTER 5: TRANSITION ELEMENTS (d-BLOCK)

• Properties and Explanations:

  • Variable Oxidation States: Due to the participation of both $(n-1)d$ and $ns$ electrons in bonding.

  • Coloured Ions: Result from $d\text{-}d$ electronic transitions where electrons absorb light in the visible spectrum.

  • Catalytic Activity: Transition metals provide a surface for reactants to sit on or form unstable intermediates due to variable valency.

  • Magnetic Properties: Presence of unpaired electrons leads to paramagnetism.

CHAPTER 6: CHEMICAL ENERGETICS

• Energy Changes:

  • System: The part of the universe under study (the reaction).

  • Surroundings: Everything else around the reaction.

• Enthalpy Change ($\Delta H$):

  • Exothermic Reaction: Heat is released to surroundings. $\Delta H$ is negative (\Delta H < 0).

  • Endothermic Reaction: Heat is absorbed from surroundings. $\Delta H$ is positive (\Delta H > 0).

• Bond Energetics:

  • Bond breaking is an endothermic process.

  • Bond making is an exothermic process.

CHAPTER 7: RATES OF REACTIONS

• Collision Theory: For a reaction to occur, particles must collide with sufficient energy (Activation Energy, $E_{a}$) and correct orientation.

• Factors influencing rate:

  • Concentration/Pressure: Increases collision frequency.

  • Temperature: Increases both frequency and the number of particles with energy $\ge E_{a}$.

  • Catalyst: Provides an alternative pathway with a lower activation energy.

CHAPTER 8: REVERSIBLE REACTIONS AND EQUILIBRIUM

• Dynamic Equilibrium: A state where the forward and backward reactions occur at the same rate, and concentrations remain constant.

• Le Chatelier’s Principle Application:

  • Haber Process ($N<em>{2} + 3H</em>{2} \rightleftharpoons 2NH_{3} + \text{Heat}$):

  • High pressure favors the production of ammonia ($4\text{ moles} \rightarrow 2\text{ moles}$).

  • Low temperature favors the exothermic forward reaction (but moderate temp is used for rate).

CHAPTER 9: ALCOHOLS

• Preparation of Ethanol:

  • Fermentation: $C<em>{6}H</em>{12}O<em>{6} \xrightarrow{\text{Zymase}} 2C</em>{2}H<em>{5}OH + 2CO</em>{2}$.

  • Hydration of Ethene: $C<em>{2}H</em>{4} + H<em>{2}O \xrightarrow{H</em>{3}PO<em>{4}} C</em>{2}H_{5}OH$.

• Reactions:

  • Combustion: $C<em>{2}H</em>{5}OH + 3O<em>{2} \rightarrow 2CO</em>{2} + 3H_{2}O$.

  • Esterification: $\text{Alcohol} + \text{Carboxylic Acid} \rightarrow \text{Ester} + \text{Water}$.

PREFACE AND CURRICULUM OVERVIEW

The Class X Science curriculum was designed and written in accordance with the Science Curriculum Framework prepared by the Royal Education Council (REC) of the Ministry of Education in Bhutan. This syllabus is part of a major reform initiated in 2013 that focuses on a spiral relationship in content flow across key stages, aiming to maximize learning efficiency for higher classes. The textbook features intended learning objectives for each topic, self-evaluation questions, and practical activities designed to explain abstract concepts. Chapters include summaries for time-efficient revision, exercises, specimen papers, and a glossary. To increase student interest and interactivity, topics are introduced using cartoon concepts. The pedagogical approach blends cooperative learning structures with transformative pedagogy to engage all students, establishing Chemistry as a foundational tool for those pursuing future studies in the science stream.

ASSESSMENT IN CHEMISTRY

Assessment in Chemistry is a process of measuring student achievement in knowledge, skills, and attitude, and it must remain accurate, objective, and valid. Its purpose is to inform teaching and learning, help students set personal goals, provide report card grades for stakeholders, and motivate learners. The domains of assessment include Scientific Knowledge (SK), covering laws and concepts like the mole concept and energetics; Working Scientifically (WS), which involves logic, technology, and communication; and Scientific Values and Attitudes (SV), addressing ethical and environmental implications. Assessment types include Continuous Formative Assessment (CFA) for daily diagnostics, Continuous Summative Assessment (CSA) for graded performance evaluation, and term-end Summative Assessment (SA) covering Bloom's Taxonomy. Weightages are distributed across Term 1 ($30\%$), Term 2 ($50\%$), Project Work ($5\%$), Practical Work ($5\%$), and class tests/homework ($10\%$).

CHAPTER 1: GAS LAWS

Gases are characterized by molecules in constant random motion with large intermolecular distances and weak forces. Their physical properties are described by the variables of Temperature ($T$), Pressure ($P$), and Volume ($V$). According to the Kinetic Molecular Theory (KMT), gas particles are in continuous, rapid motion, and collisions between them or the container walls are perfectly elastic. The average kinetic energy of these particles is directly proportional to the absolute temperature ($K \propto T$). Standard units for measurement include degrees Celsius or Kelvin ($T(K) = t(^{\circ}C) + 273$) for temperature, and Pascals, atmospheres, or mm Hg for pressure ($1\text{ atm} = 760\text{ mm Hg} = 101.325\text{ kPa}$). Volume is typically measured in Litres, where $1\text{ Litre} = 1\text{ dm}^3$.

Boyle’s Law establishes the pressure-volume relationship, stating that at a constant temperature, the volume of a gas sample is inversely proportional to its pressure ($PV = k$ or $P<em>{1}V</em>{1} = P<em>{2}V</em>{2}$). Charles’ Law describes the volume-temperature relationship, noting that at constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature ($\frac{V}{T} = k$ or $\frac{V<em>{1}}{T</em>{1}} = \frac{V<em>{2}}{T</em>{2}}$). Absolute zero is defined as the theoretical temperature of $-273.15^{\circ}C$ or $0 K$ where volume becomes zero. Avogadro’s Law states that equal volumes of all gases under similar conditions contain an equal number of molecules, with one mole of ideal gas occupying $22.4\text{ Litres}$ at STP. These relationships are combined into the Combined Gas Law ($\frac{P<em>{1}V</em>{1}}{T<em>{1}} = \frac{P</em>{2}V<em>{2}}{T</em>{2}}$) and the Ideal Gas Equation ($PV = nRT$), where $R$ is the universal gas constant ($0.0821\text{ L atm K}^{-1} \text{ mol}^{-1}$). Finally, Dalton’s Law of Partial Pressures states that the total pressure exerted by a mixture of non-reacting gases is equal to the sum of the partial pressures of its constituents ($P<em>{total} = P</em>{1} + P<em>{2} + \dots + P</em>{n}$).

CHAPTER 2: THE MOLE CONCEPT AND STOICHIOMETRY

Relative atomic mass ($A<em>{r}$) is the average mass of an atom relative to $\frac{1}{12}$ of the mass of a Carbon-12 atom, while relative molecular mass ($M</em>{r}$) is the sum of the relative atomic masses of all atoms present in a molecule. The mole is defined as an amount of substance containing $6.023 \times 10^{23}$ particles (Avogadro's Number, $N_{A}$). The number of moles ($n$) can be determined using the formula $n = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}$. Chemical formulas include the empirical formula, which provides the simplest whole-number ratio, and the molecular formula, which gives the actual number of atoms present ($\text{Molecular Formula} = n \times \text{Empirical Formula}$). Percentage composition is calculated by dividing the total mass of an element in a compound by the molar mass of the compound and multiplying by $100\%$.

CHAPTER 3: METALLURGY

Minerals are natural inorganic substances found in the earth's crust, while ores are minerals from which metals can be economically extracted. To remove impurities known as gangue, a flux (such as $CaO$ or $SiO_{2}$) is added during processing to form a waste product called slag ($\text{Flux} + \text{Gangue} = \text{Slag}$). Concentration methods include gravity separation based on density, magnetic separation for magnetic ores like Magnetite, and froth floatation for sulfide ores using pine oil. Chemical extraction involves calcination, where ore is heated without air to remove moisture, and roasting, where sulfide ores are heated in excess air to produce oxides. Metals are often mixed to form alloys, such as stainless steel (Iron, Chromium, Nickel), brass (Copper, Zinc), and bronze (Copper, Tin).

CHAPTER 4: HALOGENS (GROUP 17)

Halogens in Group 17 have distinct physical properties: Fluorine is a pale yellow gas, Chlorine is a greenish-yellow gas, Bromine is a reddish-brown liquid, and Iodine is a dark violet solid. Chemical reactivity decreases down the group (F > Cl > Br > I), and these elements form halide ions ($X^{-}$) by gaining one electron. They are also known as strong oxidizing agents.

CHAPTER 5: TRANSITION ELEMENTS (d-BLOCK)

Transition elements exhibit several unique properties due to their electronic configuration. They show variable oxidation states because both $(n-1)d$ and $ns$ electrons participate in bonding. Many form colored ions due to $d\text{-}d$ electronic transitions where electrons absorb light in the visible spectrum. Their catalytic activity stems from providing a surface for reactants or forming unstable intermediates through variable valency. Additionally, the presence of unpaired electrons leads to paramagnetism.

CHAPTER 6: CHEMICAL ENERGETICS

Chemical energetics defines the reaction as the system and everything else as the surroundings. Enthalpy change ($\Delta H$) measures the energy flow; in an exothermic reaction, heat is released to the surroundings and $\Delta H$ is negative.

CHAPTER 7: RATES OF REACTIONS

Collision Theory states that for a reaction to occur, particles must collide with sufficient Activation Energy ($E<em>{a}$) and correct orientation. The reaction rate is affected by concentration and pressure, which increase collision frequency, and temperature, which increases both frequency and the number of particles exceeding $E</em>{a}$. A catalyst speeds up the rate by providing an alternative pathway with a lower activation energy.

CHAPTER 8: REVERSIBLE REACTIONS AND EQUILIBRIUM

Dynamic equilibrium is a state where the forward and backward reactions occur at the same rate, ensuring constant concentrations. Le Chatelier’s Principle is applied in the Haber Process ($N<em>{2} + 3H</em>{2} \rightleftharpoons 2NH_{3} + \text{Heat}$), where high pressure favors ammonia production and moderate temperatures are used to balance the reaction rate with the exothermic forward preference.

CHAPTER 9: ALCOHOLS

Ethanol is prepared by the fermentation of glucose using the enzyme Zymase ($C<em>{6}H</em>{12}O<em>{6} \rightarrow 2C</em>{2}H<em>{5}OH + 2CO</em>{2}$) or by the hydration of ethene ($C<em>{2}H</em>{4} + H<em>{2}O \xrightarrow{H</em>{3}PO<em>{4}} C</em>{2}H<em>{5}OH$). Major reactions include combustion ($C</em>{2}H<em>{5}OH + 3O</em>{2} \rightarrow 2CO<em>{2} + 3H</em>{2}O$) and esterification, where an alcohol reacts with a carboxylic acid to produce an ester and water.