Notes, summaries, assignments, exams, and exercises for Chemistry for Secondary education

Understanding Substances and Mixtures

Substances are formed by identical particles, which can be either atoms or molecules. Within the realm of substances, we distinguish between:

• Elements: Pure substances that cannot be decomposed into simpler substances by chemical means.
• Compounds: Substances whose molecules are formed by two or more different elements chemically bonded together.

Mixtures: Combinations of two or more substances that are not chemically bonded.

Types of Mixtures

• Homogeneous Mixtures: Mixtures where components are uniformly distributed and indistinguishable, appearing as a single phase.
• Heterogeneous Mixtures: Mixtures where components are not uniformly distributed and are visibly distinct, appearing as multiple phases.

Mixtures can...

ELEMENT: A substance formed by atoms that are equal, e.g., we take a piece of earth; all Fe atoms are equal. All the elements are in the periodic table. Compounds are formed when different atoms combine with each other, e.g., water (H₂O) -> H₂O. Each symbol is assigned to make it easier to study.

PERIODIC TABLE

1. Elements are sorted in increasing order of their atomic number.
2. Elements in the same period have the same energy levels or layers of electrons.
3. Elements that have the same last level of electrons and similar chemical properties are located in the same vertical group.

There are 7 periods. The groups coincide in addition to having the same number of electrons in the outer shell. The classification of the outer electrons is important for...

Atomic Structure and Properties

Atomic Models

The concept of matter, initially considered indivisible according to Dalton, is presented with a discontinuous structure based on cathode rays (Thomson) and canal rays (Goldstein).

Rutherford considered the atom to consist of a small, hard core containing protons and neutrons, with electrons rotating around this core.

Bohr proposed that electrons in the atom are located in specific energy levels and sublevels, representing the distribution of electrons around the nucleus.

Key Atomic Definitions

Atomic Number (Z)

Atomic number (Z): Z = Number of Protons = Number of Electrons (in a neutral atom).

Mass Number (A)

Mass number (A): A = Number of Protons + Number of Neutrons.

Isotopes

Isotopes: Atoms of the same...

Separation Techniques for Homogeneous Mixtures

Homogeneous mixtures (liquid-solid):

Distillation, Vaporization, and Crystallization

Distillation: This is a technique that allows us to separate and recover components of a liquid solution. We must keep in mind: do not fill the flask to more than half its capacity. Before heating the flask with the solution, we place porous pieces of porcelain or glass beads into the liquid. The reason is so that boiling occurs with small bubbles and without splashing. The coolant water enters at the bottom and exits at the top.

Vaporization: Heat the solution in a porcelain capsule until the liquid has evaporated completely.

Crystallization: The solution is left in a crystallizer because the liquid evaporates at ambient...

Subatomic Particles: Components of the Atom

Atoms are composed of tiny particles called subatomic particles:

• Electron

  Discovered by J.J. Thomson in 1897 while studying cathode rays produced in an evacuated glass tube with a voltage of about 10,000 volts. The electron is a negatively charged particle (on the order of $10^{-19}$ coulombs) with a mass of approximately $10^{-31}$ kg.

• Proton

  Discovered by Ernest Rutherford in 1919. It is a positively charged particle with a magnitude equal to the electron's charge and a mass approximately 1,840 times greater than the electron's mass.

• Neutron

  Discovered by James Chadwick in 1932. He worked with radiation emitted by beryllium when bombarded with alpha particles (originating from radioactive emissions). The

1. True or False Statements

a) True

b) True

c) True / FALSE, if the hypothesis has not been demonstrated.

2. Measurement Units and Properties

a) Size: m³ is a unit of volume and can be used in moderation.

b) Scalability: It does not scale; it is not a unit of restraint.

c) Magnitude Measurement: Magnitude can be measured in K (Kelvin).

3. Units of Measurement

• Length - Meter - m
• Mass - Kilogram - kg
• Time - Second - s
• Temperature - Kelvin - K
• Intensity of Current - Ampere - A

4. Unit Conversions

a) 2.5 mm x (1 m / 1,000 mm) = 0.0025 m = 2.5 x 10^-3 m

b) 0.53 mg x (1 g / 1,000 mg) x (1 kg / 1,000 g) = 0.00000053 kg = 5.3 x 10^-7 kg

c) 3 h x (3,600 s / 1 h) = 10,800 s = 1.08 x 10⁴ s

5. Calculations with Significant Figures

a) 8.34 x 3.1456 = 26.234304 = 26.2

b) 4.00...

Heterogeneous Mixtures: Composite Nature

Heterogeneous mixtures consist of substances that do not mix uniformly, similar to water and oil. These can be separated using various physical methods:

• Solid-Solid Mixtures: Separated by magnetization (if one component is magnetic), manual sorting, or sieving (if particle sizes differ).
• Solid-Liquid Mixtures: Separated via sedimentation, decanting, centrifugation, or filtration.
• Immiscible Liquids: Separated using a separating funnel or normal settling based on density differences.

Homogeneous Mixtures and Solutions

Homogeneous mixtures have a uniform composition throughout. A solution is formed by two or more substances in variable proportions:

• Solvent: The component present in the largest quantity.
• Solute:

Pure Substances

A pure substance is a material that maintains a constant composition regardless of the conditions. Pure substances cannot be decomposed into other substances using simple chemical procedures.

Elements and Compounds

• Compounds: Pure substances that can be decomposed into simpler ones through a chemical process.
• Elements: Pure substances that cannot be decomposed into simpler substances by any procedure.

Mixtures

A mixture is matter that results from the combination of several pure substances that can be separated using physical means. There are two primary types:

• Homogeneous: A mixture in which components are indistinguishable by conventional optical procedures.
• Heterogeneous: A mixture in which components can be distinguished by conventional

Heterogeneous Mixture Separation

• Filtration: Separates a solid from a liquid using filter paper that allows the liquid to pass while retaining the solid.
• Decantation: Separates two immiscible liquids with different densities.
• Magnetic Separation: Uses a magnet to extract ferromagnetic components from a mixture.
• Centrifugation: Separates suspensions of solids and liquids by spinning the mixture to force solids outward.

Homogeneous Mixture Separation

• Chromatography: Separates liquids with different densities and colors using paper, where the lower density liquid rises.
• Extraction by Solvents: Separates two liquids based on their different solubilities in a specific solvent.
• Distillation: Separates two liquids with different boiling points by heating

Hydrochloric Acid (HCl) Titration

Theory

Titration of a strong acid and a strong base involves a neutralization reaction:

$$\text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O}$$

During titration, the pH of the solution taken in the conical flask changes as the other solution is added from the burette. If NaOH is added from the burette and HCl is taken in the conical flask, during the titration the pH of the solution in the conical flask will increase.

Procedure

1. Take a clean burette, rinse it with 0.1 M NaOH solution, and then fill it with this solution.
2. Rinse the pipette with 0.1 M HCl solution. Pipette out 10.0 mL of 0.1 M HCl into the conical flask and add about 2–3 drops of