Notes, summaries, assignments, exams, and exercises for Chemistry for Other courses

Reactions in Aqueous Solutions

Acid and Base Definition According to Bronsted-Lowry

Acid: A substance capable of donating protons.

Base: A substance capable of accepting protons.

For a substance to act as an acid, it must be in the presence of another substance that acts as a base and accepts the proton transferred by the acid. In aqueous solutions, water plays the role of both acid and base.

• When an acid donates protons, it becomes a species capable of accepting protons, called the conjugate base.
• When a base accepts protons, it is transformed into a species capable of donating protons, i.e., an acid, called the conjugate acid.

Equilibrium of Water Dissociation and the Concept of Kw

Water behaves as both an acid and a base according to the reaction:...

Method 1: The Chemical Path

Δ_rH_m = Molar Enthalpy (kJ/mol)

Trigger: Only when a chemical reaction has taken place.

• ΔH_rxn = Enthalpy change of the whole reaction
• Δ_rH_m = Q_rxn / n
• Q_rxn = Heat of Reaction (kJ)

H₂O data: Mass or volume of water given. Chemical data: Mass, concentration, or moles of reactant burnt or dissolved.

Q_rxn = -Q_water

Note: If chemicals and water are involved in the reaction, flip the signs for Q_rxn and Q_water; if it is just warming, do not flip the signs.

Method 2: The Physical Phase Change Path

No chemical reaction; only temperature change or physical change occurs.

Scenario A: Changing Temperature (Substance stays same)

Q = mcΔT

• Units: Q (J or kJ) | m (g) | c (J/g·°C) | ΔT (°C)

Scenario B: Constant Temperature (Melting, boiling,

Periodic Table of Elements

7s 7p
6s 6p 6d
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s

Elements are sorted by atomic number and grouped by chemical and physical properties, with 18 groups and 7 periods.

Group

A group consists of elements that have a similar electron configuration at the highest energy level. They have the same number of electrons in the same type of sub-levels, although at different energy levels. The chemical characteristics are similar and depend on the outermost electrons of the atoms. There are 18 groups.

Period

A period comprises all elements whose maximum energy level is the same. There are 7 periods: the 1st has 2 elements, the 2nd and 3rd have 8 elements, the 4th and 5th have 18 elements, and the 6th has 32 elements.

Periodic

Crystalline Solids

Crystal Lattice

The main characteristic of crystalline solids is a regular and repeating pattern of constituent particles. A crystal lattice is a three-dimensional arrangement of points in space, representing the arrangement of these particles.

Unit Cells

Unit cells are the smallest repeating units in a crystal lattice. They are broadly divided into two categories:

• Primitive Unit Cells: Constituent particles are present only at the corners.
• Centred Unit Cells: Contain particles at positions other than corners, in addition to those at the corners. There are three types of centered unit cells:
  • Body-Centred Unit Cells: Contain one particle at the body-center, besides those at the corners.
  • Face-Centred Unit Cells: Contain one particle

Correction of Free SO2

Determining the free SO2 content requires knowing the fraction of SO2 that can combine with certain wine components. This combination is referenced in index tables.

Dose of SO2 and Timing of Sulfite Addition

Initial Sulfiting

The first sulfite addition occurs immediately after pressing or squeezing the juice. This step is crucial to:

• Prevent fermentation under inadequate conditions.
• Aid in selecting appropriate yeasts.
• Prevent enzymatic browning and oxidation.

This initial sulfiting is of low intensity, typically around 45 mg/L total SO2.

Post-Fermentation Adjustment

After fermentation, the SO2 level must be restored, usually after the wine has been decanted, unless malolactic fermentation is desired. The target dose is 20 mg/L...

1. Sources of Water

2. Impurities in Water

3. Hardness of Water

Definition

Hardness...

Discover how to bake incredibly moist and gooey homemade brownies from scratch, achieving a texture similar to your favorite box mix without any artificial additives. This simple recipe highlights key ingredients and techniques for perfect results every time.

Essential Ingredients for Your Brownies

• Vanilla Extract: A half teaspoon of vanilla extract significantly enhances the rich chocolate flavor.
• Eggs + Water: Michelle's secret for a moist, gooey texture, similar to box mix brownies, without commercial emulsifiers. Since this recipe does not contain baking powder, eggs are crucial for helping the brownies rise in the oven.
• Powdered Sugar: The key to achieving that classic box-mix brownie texture! Powdered sugar contains cornstarch, which naturally

Electroanalytical Fundamentals

• Common electroanalytical methods
• Electrochemical cell fundamentals
• Potential in electrochemical cells
  • No current: Nernst Equation
  • With current: Ohmic Resistance and Polarization

What is Potentiometry?

• Potentiometry involves measuring the electrochemical potential between two electrodes in a solution. This potential difference (voltage) is related to the concentration of ions in the solution according to the Nernst Equation.

General Principles of Potentiometry

• Reference Electrode:

  • Known, fixed potential
    • Silver/Silver Chloride (Ag/AgCl)
    • Calomel

• Indicator Electrode:

  • Sensitive to concentration of analyte
    • Metallic
    • Ion-Selective
• Measure E_cell (negligible current flows through the cell)
• Correct E_ref and E_j (Junction Potential)
• Compute

The Topping Process in Petroleum Refining

The oil is heated to 350°C and sent to a fractionating tower, a metal structure 50 meters high, containing many bubbling trays. A bubbling tray is a perforated plate mounted horizontally; each hole features a small tube with a cap. This design forces hot gases within the tower to pass through the cooler liquid retained by the plates. Once the liquid level rises, it spills over and falls to the plate below.

The temperature in the fractionating tower is progressively graded from 350°C at its base to less than 100°C at its head. During continuous operation, hot oil enters the tower while specific fractions are extracted at convenient heights. These fractions correspond to distinct characteristics, though...

Required Practical 1: Making Soluble Salts

Aim

To prepare a pure, dry sample of a soluble salt from an insoluble base, for example, making copper(II) sulfate from copper(II) oxide.

Method

1. Add excess copper(II) oxide to warm sulfuric acid and stir.
2. Filter the solution to remove the excess, unreacted base.
3. Gently evaporate the water from the filtrate to crystallize the salt.
4. Leave the solution to cool and then dry the resulting crystals.

Key Points to Remember

• Ensure excess base is used to neutralize all the acid.
• Avoid boiling the solution; use gentle heating to prevent it from spitting.
• Filter carefully to remove all unreacted solid for a pure salt solution.

Required Practical 2: Neutralization by Titration

Aim

To determine the concentration of an acid or...