Mod 5
What does the term "dynamic equilibrium" mean?
The forward and reverse reactions occur at the same rate
Name a strong acid and a strong base
HCl, NaOH
What is the functional group present in aldehydes?
The functional group is the aldehyde group: –CHO.
Name one pollutant produced during combustion of fossil fuels.
One pollutant is carbon monoxide (CO) or sulphur dioxide (SO₂).
What is the atomic number of magnesium?
Atomic number of magnesium is 12.
State Le Chatelier's Principle
If a system at equilibrium is disturbed by changing conditions, the system will shift to oppose the change and restore equilibrium.
Briefly explain the Bronsted-Lowry definition of acids and bases.
Bronsted-Lowry acids donate protons (H⁺); Bronsted-Lowry bases accept protons.
Give the IUPAC name for CH₃CH₂CH₂CH₂OH.
CH₃CH₂CH₂CH₂OH is called butan-1-ol.
Give a real-world example where chemistry is applied for environmental protection.
Using catalytic converters in cars to reduce NOx and CO emissions is an example of chemistry applied to protect the environment.
Write the equation for calculating molarity.
Molarity (M) = moles of solute / litres of solution
For the reaction N2 + 3H2 (eq arrow) 2NH3 + heat
What happens to the equilibrium position if the pressure is increased?
Increasing the pressure shifts towards the side with fewer moles of gas molecules.
Towards the ammonia (right)
Calculate the pH of a 0.003 M solution of HNO₃.
For strong acid HNO₃:
pH = -log[H⁺] = -log(0.003) ≈ 2.52
Describe the mechanism of the addition reaction between ethene and bromine, including a structural equation.
The double bond in ethene reacts with bromine:
C₂H₄ + Br₂ → C₂H₄Br₂
The reaction involves the breaking of the π bond, forming a dibromoalkane via electrophilic addition.
Describe how chromatography can be used to identify components in a dye sample and discuss its limitations.
Chromatography separates components based on their movement through a stationary phase; it identifies dye components based on retention factor (Rf values). Limitations include overlapping spots, inability to identify compounds without standards.
A compound contains 40% carbon, 6.7% hydrogen, and 53.3% oxygen. Calculate its empirical formula.
Assume 100g sample:
C = 40g (3.33 mol), H = 6.7g (6.7 mol), O = 53.3g (3.33 mol)
Ratio: C:H:O = 3.33:6.7:3.33 → 1:2:1
Empirical formula: CH₂O
A solution containing the ion Fe3+ appears yellow; after adding SCN-, it turns deep red. Explain how this demonstrates equilibrium and the effect of adding a reactant on position.
Adding SCN⁻ increases the concentration of a reactant in the equilibrium: Fe³⁺ + SCN⁻ ⇌ Fe(SCN)²⁺. The equilibrium shifts right, producing more Fe(SCN)²⁺ (deep red), demonstrating Le Chatelier’s Principle. The intensity of the red colour shows the shift due to increased SCN⁻.
A buffer solution contains 0.1 M acetic acid and 0.1 M sodium acetate. If a small amount of HCl is added, explain in detail what happens to the pH and why the buffer resists changes.
The acetic acid/sodium acetate buffer neutralises added HCl (the acetate ion reacts with added H⁺ to form acetic acid), so the pH changes only slightly. The buffer resists changes by converting strong acids/bases into weak ones, maintaining pH.
Outline the steps and reagents to convert an alkene to a primary alcohol and then to a carboxylic acid, including reaction conditions and relevant equations.
Discuss in detail the multiple steps involved in municipal water purification and the underlying chemistry for each step (coagulation, filtration, chlorination).
Explain in detail the differences between metallic, ionic, and covalent lattices. Include discussion of structure, bonding and physical properties (melting point, conductivity, solubility).
Consider a reaction: 2NO₂(g) ⇌ N₂O₄(g), ΔH = -58 kJ/mol. At a certain temperature, a sealed container contains only NO₂ at 1.00 atm pressure. Describe how the equilibrium position and the concentrations of NO₂ and N₂O₄ will change if the temperature is significantly decreased, and explain your reasoning with reference to entropy and enthalpy.
Decreasing the temperature favours the exothermic direction (formation of N₂O₄). The equilibrium shifts right, increasing N₂O₄ and decreasing NO₂ concentration. Lower entropy (fewer gas molecules) is disfavoured at high temperatures, but at lower temperatures the exothermic reaction becomes dominant, so enthalpy change drives equilibrium towards N₂O₄.
Calculate the pH at equivalence for the titration of 50.0 mL of 0.1 M acetic acid (pKa = 4.76) with 0.1 M NaOH. Explain the steps and reasoning involved.
At equivalence, all acetic acid is converted to acetate ion. The solution contains 0.1 M sodium acetate in 100 mL (0.05 M).
Acetate hydrolyses: CH₃COO⁻ + H₂O ⇌ CH₃COOH + OH⁻
Use Kb for acetate: Kb = Kw/Ka = 10⁻¹⁴/1.74×10⁻⁵ ≈ 5.75×10⁻¹⁰
[OH⁻] = √(Kb × [CH₃COO⁻]) = √(5.75×10⁻¹⁰ × 0.05) ≈ 5.4×10⁻⁶ M
pOH ≈ 5.27 → pH ≈ 14 - 5.27 = 8.73
Outline a synthetic pathway to convert ethene (C₂H₄) to ethanoic acid (acetic acid). Include necessary reagents, intermediates, and key reaction conditions.
Explain how the use of ammonia in agriculture can impact both crop yield and the environment. Include a brief explanation of the Haber process and environmental issues such as eutrophication.
Ammonia is produced industrially via the Haber process (N₂ + 3H₂ ⇌ 2NH₃) and used in fertilisers to increase crop yields by providing essential nitrogen. However, excess application can lead to runoff into waterways, causing eutrophication (nutrient enrichment leads to algal blooms and oxygen depletion), negatively impacting aquatic ecosystems.
What is the full chemical name for water
dihydrogen monoxide