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

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

Answer Key for Solubility Equilibrium

1A, 2C, 3B, 4C, 5A, 6C, 7C, 8B, 9A, 10D, 11D, 12A, 13B, 14C, 15C, 16D, 17B

Detailed Solutions for Solubility Problems

Problem 1: Net Ionic Equation and Precipitation

1a. Net Ionic Equation:
Pb²⁺ + 2Cl^- → PbCl₂(s)

1b. Precipitation Calculation:
moles Pb²⁺ = (0.0150)(0.0500) = 0.00075
moles Cl^- = (0.0350)(0.0850) = 0.002975
total volume = 0.0500 L

[Pb²⁺] = 0.00075 / 0.0500 = 0.0150 M
[Cl^-] = 0.002975 / 0.0500 = 0.0595 M

Q = [Pb²⁺][Cl^-]² = (0.0150)(0.0595)²
Q = 5.3 × 10^-5
K_sp = 1.6 × 10^-5
Since Q > K_sp, a precipitate indeed forms.

Problem 2: Calculating Ksp for Silver Sulfate

2a. K_sp of Ag₂SO₄:
moles = mass / molar mass
moles = (7.2 × 10^-4) / 311.8 = 2.31 × 10^-6 mol

s = moles / volume
s = (2.31 × 10^-6) / 0.0500 = 4.62... Continue reading "Solubility Equilibrium and Ksp Practice Problems" »

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" »

To convert from decimal inches. A fraction of an inch.
Multiplied by 128 to decimal and simplifying the result by 128.

Convert decimal to a fraction of an inch inch

Examples:
1) Convert 0.250 "a fraction of an inch
Applying the rule, we have: (0.250 "* 128) / 128 = 32/128 = ¼"
2) Convert 1.750 "a fraction of an inch
Applying the rule, we have: (1,750 '* 128) / 128 = 1 96/128 = 1 ¾ "
3) Convert 2.953 "a fraction of an inch
Applying the rule, we have: (2.953 "* 128) / 128 = 2 122/128 = 2 61/64"
4) Convert 12.812 "a fraction of an inch
Applying the rule, we have: (12.812 "* 128) / 128 = 12 104/128 = 12 13/16"


To convert from mm. A fraction of an inch. Should be carried mils.
(Divide by 25.4) and then multiplying by 128 and simplify

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" »