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

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" »

Anions: Definition and Characteristics

An anion is an ion (an atom or molecule) that possesses a negative electrical charge, meaning it has an excess of electrons. Anions are typically described with a negative oxidation state. They are broadly classified into two main types: monatomic and polyatomic.

Monatomic Anions

Monatomic anions are typically formed when nonmetals gain electrons to complete their valence shell.

Traditional Nomenclature (Monatomic)

These are named using the word ion followed by the name of the nonmetal, ending in the suffix -ide. (Note: Amide and Cyanide are often included here for simplicity, though technically polyatomic.)

• Cl^-: Chloride ion
• H^-: Hydride ion
• S^2-: Sulfide ion
• NH₂^-: Amide ion
• CN^-: Cyanide ion

Systematic Nomenclature

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