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

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

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⁺)

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" »

Bonding

Formal Charge: # Valence Electrons - (Nonbonding Electrons + 1/2 Bonding Electrons)

Gases

STP = Standard Temperature and Pressure (273 K or 0°C and 1 atm)

Ideal Gas Law

R = 0.0821 atm x L / (mol x K)

• Pressure (P): Always in atm
  • 760 mmHg = 1 atm
  • 760 Torr = 1 atm
  • 101,326 Pascal = 1 atm
• Temperature (T): Always in Kelvin
• # of Moles (n)
• Volume (V): Always in Liters

Boyle's Law

Occurs when T and n are constant.

Charles's Law

Occurs when P and n are constant.

Avogadro's Law

Occurs when P and T are constant.

Gay-Lussac's Law

Occurs when V and n are constant.

Combined Gas Law

n is constant.

Test

1. a) Valence Electrons for Na⁺ = 0
2. b) Which of the following does not have an octet around the central atom: BCl₃
3. d) A triple bond has a bond order of: 3
4. c) Least electronegative

The environment plays an important role in our lives and people wouldn't be able to live without it. However, we are polluting it every day and it needs to stop. As individuals, we can do lots of things to solve this issue, and this essay will focus on two of them - recycling and the efficient use of energy.

According to recycling, it is the easiest way to see an immediate change and everybody can do it. First, recycling bins are a great method of dividing our waste into paper, plastic, glass, etc., and they can be easily found in every city. Another idea is to reuse the things we have at home and make them new. For example, turning …. 

When it comes to the use of energy, there are many things we can do, especially at home. When we talk about... Continue reading "I choose to live" »

Q#6.3: Define (i) Crystal lattice (ii) Unit Cell.

Ans.(i) Crystal Lattice.

A particular three-dimensional arrangement of particles (atoms, ions, molecules) in a crystal is called a crystal lattice.

In a crystal lattice, particles are located at definite positions in space. These positions are represented by points in a crystal and are called lattice points or lattice sites. This arrangement is called a crystal lattice or space lattice. A crystal lattice actually shows the shape of a crystal.

(ii) Unit Cell.

The smallest geometrical portion of the crystal which is used to build up the whole crystal. OR

If is the smallest portion of a crystal lattice which includes all the positions of each type of particle in the crystal. For example, a cubic crystal... Continue reading "Crystal Lattice and Unit Cell" »

An ion is an atom which has more or less electrons than protons

Hazard Symbols

Hazard symbols explain why a substance must be handled carefully.

Air Pollution from Burning Fossil Fuels

Complete combustion - the fuel reacts completely with oxygen, e.g.:

hydrocarbon + oxygen → carbon dioxide + water

Incomplete combustion - the fuel only partly reacts with oxygen, e.g.:

hydrocarbon + oxygen → carbon dioxide + water + carbon monoxide + carbon (soot)

Impurities in fossil fuels, such as sulfur, also react with oxygen when heated:

sulfur + oxygen → sulfur dioxide

At the very high temperatures in vehicle engines, nitrogen gas from the air reacts with oxygen:

nitrogen + oxygen → nitrogen oxides

Many products from burning fossil fuels are pollutants; they harm habitats and their organisms.

Acid Rain

Acid rain is rainwater... Continue reading "Combustion, Oxidation, and Environmental Impact" »

C

Circumnavigate

To sail or travel all the way around.

Citadel

A fortress defending a city.

Clandestine

Concealed or secret for an evil purpose.

Classic

Of the highest quality.

Cleave

To cling.

Climatic

Having to do with the climate.

Cloister

Covered walk, with columns on one side.

Clone

An exact duplicate.

Clout

A blow.

Cloy

To cause to feel too full when eating; overly sweet.

Coddle

To baby.

Cogitate

To ponder.

Cohort

A group.

Commemorate

To honor the memory of.

Commiserate

To express sorrow or sympathy for.

Commodious

Spacious, roomy.

Compatible

Harmonious.

Competent

Capable.

Compile

To gather together.

Comply

To act or be in accordance with.

Composed

Calm.

Compromise

A settlement of differences in which each side gives up something.

Compunction

Remorse.

Concave

Curved inward.

Concede

To