Notes, summaries, assignments, exams, and problems for Chemistry

Part I: Temperature and Thermometers

Basic Concepts and Scales

1. Name the Three Scales of Temperature.

Ans: The three scales of temperature are:

• Celsius
• Fahrenheit
• Kelvin

2. How Are Temperature and Hotness Related?

Ans: Temperature and hotness of a body are directly related. The hotter a substance is, the higher its temperature.

3. Reading a Laboratory Thermometer: Eye Level Precaution

Ans: While reading the temperature on a laboratory thermometer, the eye must be at the level of the mercury in the stem to avoid parallax error and ensure an accurate reading.

4. How Does a Digital Thermometer Measure Temperature?

Ans: A digital thermometer does not use mercury. It utilizes internal heat sensors (such as a thermistor or thermocouple) to measure the temperature... Continue reading "Essential Science Q&A: Temperature, Thermometers, and Space Facts" »

1. What Is Static Electricity?

Static electricity is the imbalance of electric charge accumulated on an object’s surface.

It is commonly observed in daily life, resulting in phenomena such as:

• Hair rising
• A balloon sticking to a wall

2. Atomic Structure and Electric Charge

Electric charge is determined by the components of the atom:

• Proton: Positive (+) charge (located in the nucleus)
• Neutron: Neutral (0) charge (located in the nucleus)
• Electron: Negative (–) charge (orbits the nucleus)

Charge states are defined by the balance of protons and electrons:

• Neutral Atom: Equal number of protons and electrons
• Positive Charge: More protons than electrons (net loss of electrons)
• Negative Charge: More electrons than protons (net gain of electrons)

3. Methods

Vernier Caliper

A Vernier caliper is an instrument for making very accurate linear measurements introduced in 1631 by Pierre Vernier of France. It uses two graduated scales: a main scale similar to that on a ruler and an auxiliary scale, the vernier, which slides parallel to the main scale and enables readings to be made to a fraction of a division on the main scale. Vernier calipers are widely used in scientific laboratories and in manufacturing for quality-control measurements.

Five Rules for Determining Significant Figures

1. Non-zero digits are significant. For example, in 6575 cm there are four significant figures; in 0.543 there are three significant figures.
2. Leading zeros are not significant. Zeros that precede the first non-zero digit indicate

Catalytic Reforming Process Fundamentals

• Converts low-octane naphtha into high-octane reformate, which is used for gasoline blending and aromatics production.
• Feed is mixed with hydrogen, heated, and passed over a catalyst in fixed-bed reactors.
• Major reactions include dehydrogenation to aromatics, isomerization to branched paraffins, and mild hydrocracking.
• Operating conditions are typically 450–520 °C temperature and 10–45 atm pressure.
• The catalyst used is platinum on alumina or bimetallic Pt–Re on alumina.
• Main products are reformate, hydrogen, LPG, and light hydrocarbons.

Fluid Catalytic Cracking (FCC) Technology

1. FCC converts heavy gas oils into valuable products like high-octane gasoline, LPG, and olefins.
2. Preheated feed contacts hot,

Fundamentals of Analytical Chemistry Techniques

Analytical techniques are methods used to identify, quantify, and understand the chemical composition and structure of substances. These techniques are broadly classified into qualitative (what is present) and quantitative (how much is present) methods.

Major Analytical Methods

Common analytical techniques include:

• Gravimetric Analysis: Involves measuring the mass of a substance to determine the amount of analyte.
• Titrimetric (Volumetric) Analysis: Based on measuring the volume of a standard solution required to react with the analyte.
• Spectroscopic Methods: Measure the interaction between light and matter.
• Electrochemical Methods: Based on the measurement of electrical properties.

Preparation and Standardization

EDTA Titration and Water Hardness Calculation

EDTA Structure

EDTA (C₁₀H₁₆N₂O₈) is a hexadentate ligand that binds metal ions through four carboxyl (–COOH) groups and two amine (–NH₂) groups.

Titration Procedure (Water Hardness Test)

1. Take a 50 mL water sample.
2. Add buffer (pH 10) and Eriochrome Black T indicator (resulting in a wine-red color).
3. Titrate with EDTA until the color changes to sky blue (the end point).
4. Note the volume of EDTA used (V).

Reaction

M²⁺ + EDTA⁴⁻ → [M-EDTA]²⁻

Calculation Formula

Hardness (ppm) = (V × M × 1,000,000) / Vₛₐₘₗₔₗₑ

• M = EDTA molarity
• V = Volume of EDTA used (mL)
• Vₛₐₘₗₔₗₑ = Sample volume (mL)

Water Impurities and Boiler Problems

Hardness

The presence of calcium (Ca²⁺)

Determination of Water Hardness by EDTA Method

EDTA is the abbreviation for Ethylene Diamine Tetra Acetic acid.

Pure EDTA dissolves in water with great difficulty and in very small quantities. Conversely, its di-sodium salt dissolves quickly and completely. Hence, for common experimental purposes, the di-sodium derivative of EDTA is used.

EDTA is a hexadentate ligand. It binds metal ions present in water, such as $Ca^{+2}$ or $Mg^{+2}$, to form a highly stable chelate complex. These metal ions are bonded via oxygen or nitrogen atoms from the EDTA molecule. Therefore, this method is called complexometric titration.

Principle of the EDTA Method

The di-sodium salt of EDTA forms complexes with $Ca^{+2}$ and $Mg^{+2}$ as well as with many other metal... Continue reading "Determining Water Hardness: The EDTA Titration Method" »

1. Sources of Water

2. Impurities in Water

3. Hardness of Water

Definition

Hardness... Continue reading "Water Chemistry: Hardness, Alkalinity, and Treatment" »

Chemical Reactions

Types of Chemical Reactions

• Synthesis: A + B → AB
• Decomposition: AB → A + B
• Single Displacement: A + BC → AC + B
• Double Displacement: AB + CD → AD + CB
• Combustion: A + O₂ → H₂O + CO₂ (typically for hydrocarbons)
• Acid-Base: Acid + Base → Salt + Water
• Precipitation: Soluble Salt A + Soluble Salt B → Precipitate + Soluble Salt C

Stoichiometry and Mole Concepts

Key Stoichiometry Relationships

• Mass: 1 mole = Molar Mass (in grams)
• Volume: 1 mole = 22.4 L @ STP (Standard Temperature and Pressure)
• Particles: 1 mole = 6.022 × 10²³ particles (Avogadro's Number)
• Mole-Mole Conversions: Use coefficients from a balanced chemical equation.

Standard Temperature and Pressure (STP)

• Temperature: 0 °C (273.15 K)
• Pressure: 1 atm

Gas Laws

Preparation of Naphthalene

Naphthalene is a fused-ring aromatic hydrocarbon with two benzene rings. It can be prepared via the following methods:

• From Coal Tar: Coal tar, a by-product of coal processing, is a major source of naphthalene. It is extracted and purified using distillation followed by crystallization.
• Synthesis from Benzene: Benzene undergoes a series of reactions to form naphthalene:
  • Alkylation: Benzene reacts with alkyl halides (like methyl chloride) to form methylbenzene (toluene).
  • Cyclization: Toluene undergoes further reaction with chlorine and heat to form naphthalene.

Preparation of Anthracene

Anthracene is a tricyclic aromatic hydrocarbon consisting of three fused benzene rings. It is mainly obtained from coal tar but can also... Continue reading "Synthesis and Sources of Aromatic Hydrocarbons" »