Day: November 23, 2024

Chapter 9 Acids and Bases – Solved Exercise for Federal Board Students

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Explore solved exercises of Chapter 9 Acids-Bases Chemistry. Includes explanations of ionization, hydrolysis, buffer solutions, and acid-base reactions for college-level learners.

2. Give Short Answers

(i) What are conjugate acid-base pairs? Explain with examples.
A conjugate acid-base pair consists of two species that differ by a single proton (H⁺). The acid donates a proton to become its conjugate base, while the base accepts a proton to form its conjugate acid.
Example:

  • HCl (acid) and Cl⁻ (conjugate base)
  • NH₃ (base) and NH₄⁺ (conjugate acid)

(ii) Define Lewis acid and Lewis base. Give one example of each.

  • Lewis Acid: A substance that can accept a pair of electrons.
    Example: AlCl₃
  • Lewis Base: A substance that can donate a pair of electrons.
    Example: NH₃

(iii) Write briefly about the ionization of water.
Water ionizes slightly to produce hydrogen ions (H⁺) and hydroxide ions (OH⁻):
H2O⇌H++OH−H₂O ⇌ H⁺ + OH⁻
The ionization constant of water at 25°C is Kw=[H+][OH−]=1.0×10−14Kw = [H⁺][OH⁻] = 1.0×10-14.

(iv) Define pH and pOH. Write the values of pH for acidic, basic, and neutral solutions.

  • pH: A measure of hydrogen ion concentration:
    pH=−log⁡[H+]
  • pOH: A measure of hydroxide ion concentration:
    pOH=−log⁡[OH−]
    Values:
  • Acidic: pH<7
  • Neutral: pH=7
  • Basic: pH>7

(v) What are Ka and pKa?

  • Ka: The acid dissociation constant, representing the strength of an acid.
  • pKa: The negative logarithm of Ka
    pKa=−log⁡(Ka)
    A lower pKa indicates a stronger acid.

(vi) What is the relationship between Ka and Kb?
The product of Ka (acid dissociation constant) and Kb (base dissociation constant) of a conjugate acid-base pair is equal to the ionization constant of water (Kw):
Ka⋅Kb=Kw=1.0×10−14

(vii) Give two examples of a buffer solution.

  1. Acetic acid and sodium acetate solution
  2. Ammonium chloride and ammonia solution

(viii) How does temperature impact solubility?
The solubility of most solids increases with temperature, while the solubility of gases decreases as temperature rises.

3. Elaborate on the ionization equation of water. How does it lead to the ion-product constant of water?

Water undergoes self-ionization, producing equal concentrations of H⁺ and OH⁻ ions:
H2O+H2O⇌H3O++OH−H₂O + H₂O ⇌ H₃O⁺ + OH⁻
At 25°C, the concentrations of H⁺ and OH⁻ are both 1.0×10-7, and the ion-product constant (Kw) is:
Kw=[H+][OH−]=1.0×10−14
This constant is essential for calculating pH and pOH in aqueous solutions.

4. What are buffer solutions? Elaborate with examples. Explain their significance in acid-base reactions.

Buffer solutions resist changes in pH when small amounts of acid or base are added.

  • Example 1: Acetic acid and sodium acetate buffer
  • Example 2: Ammonium hydroxide and ammonium chloride buffer
    Significance: Buffers maintain stable pH in biological systems, industrial processes, and chemical experiments.

5. Write detailed notes on each of the following:

(i) Conjugate acid-base pairs:
These pairs consist of an acid and its conjugate base or a base and its conjugate acid, differing by one proton. Examples include:

  • HCl and Cl⁻
  • NH₃ and NH₄⁺

(ii) pH:
pH is the measure of acidity or basicity of a solution, ranging from 0 to 14. It is calculated as:
pH=−log⁡[H+]

6. What is hydrolysis? Discuss the behavior of the following salts in aqueous solutions:

(i) K2SO4: This is a neutral salt, as neither K⁺ nor SO42- hydrolyzes in water.

(ii) NH4ClNH_4Cl: This salt is acidic in water because NH4+ hydrolyzes to produce H⁺:
NH4++H2O⇌NH3+H3O+

(iii) NaNO3: This is a neutral salt, as neither Na⁺ nor NO3− hydrolyzes in water.

Chapter 11: Nitrogen and Sulfur – Solved Exercise for Federal Board Islamabad

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Nitrogen and sulphur

Find detailed solutions to Chapter 11: Nitrogen and Sulfur exercises for Federal Board Islamabad students. Includes Haber process, ammonia production, sulfur properties, and more!

Chapter 11: Nitrogen and Sulfur

1. Ammonia Production and the Haber Process

(a) Hydrogen Production:
Hydrogen is produced by reacting methane with steam in the presence of a catalyst, yielding hydrogen and carbon monoxide.

(b) Reaction Equation for the Haber Process:
N2(g)+3H2(g)⇌k=350−450∘C,200atmIronCatalyst2NH3(g)N_2 (g) + 3H_2 (g) \xrightleftharpoons[k=350-450^\circ C, 200 atm]{Iron Catalyst} 2NH_3 (g)

(c) Conditions Necessary for Efficient Working of Haber Process:

  • Temperature: 400–450°C
  • Pressure: 200 atm
  • Catalyst: Finely divided iron with promoters like K₂O and Al₂O₃

2. Composition of Exhaust Gases

(a) CO₂ Contribution:
Carbon dioxide (CO₂) contributes to about 10% of the exhaust gas composition.

(b) Water Vapor in Exhaust Gas:
Water vapor is omitted from the exhaust composition as it condenses upon cooling.

(c) Significance of Nitrogen in Exhaust Gas:
Nitrogen is unreacted air that passes through the engine without reacting.

3. Ammonium Hydroxide and Ammonium Salts

(a) Ammonium Hydroxide:
Ammonium hydroxide is a weak base used in household cleaners.

(b) Ammonium Salts:
These salts are used as fertilizers due to their high nitrogen content.

4. Safety of Ammonia Use

Ammonia is highly hazardous as it is toxic, corrosive, and can irritate skin and respiratory tracts. Proper safety measures are necessary for its handling.

Chapter 12: Sulfur

5. Properties and Uses of Sulfur and Its Compounds

(a) Sulfur and Organic Products:
Sulfur is used in manufacturing rubber, fertilizers, and sulfuric acid.

(b) Sulfuric Acid Reactions:
(i) With Water: Produces heat due to exothermic reaction.
(ii) With Sugar: Causes dehydration to form carbon.

6. Reducing Agent Behavior of Sulfur

Sulfur dioxide acts as a reducing agent, especially in reactions with oxidizing agents like chlorine.

7. Environmental Concerns:

Sulfur emissions contribute to acid rain, harming ecosystems and infrastructure.

Chapter 12: Halogens – Comprehensive Exercise Solutions for Federal Board Students

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Halogens Solution

Access detailed solutions to Chapter 12: Halogens from Federal Board Chemistry syllabus. Includes multiple-choice answers, short questions, and comprehensive explanations on reactivity, oxidizing power, and trends of halogens. Perfect for college students!

Choose the Correct Answer

  1. Which halogen has a greenish-yellow color?
    Answer: (b) Cl₂
    Explanation: Chlorine (Cl₂) gas is greenish-yellow in color and is commonly used in water treatment and as a bleaching agent.
  2. Which halogen exists in a liquid state?
    Answer: (c) Br₂
    Explanation: Bromine (Br₂) is the only halogen that is a liquid at room temperature, and it has a reddish-brown color.
  3. Which of the following is the strongest reducing agent?
    Answer: (d) I⁻
    Explanation: Iodide ion (I⁻) is the strongest reducing agent among halides because it easily donates electrons compared to other halides.
  4. Oxidizing power of which halogen is highest?
    Answer: (a) F₂
    Explanation: Fluorine (F₂) is the most electronegative element and has the highest oxidizing power among halogens.
  5. Which is the strongest acid?
    Answer: (b) HCl
    Explanation: Hydrochloric acid (HCl) is a strong acid due to its complete dissociation in water, unlike HF, which forms hydrogen bonds and is weaker.

Give Short Answers

  1. Give the order of oxidizing power of halogens.
    Answer:
    The oxidizing power of halogens decreases down the group:
    F₂ > Cl₂ > Br₂ > I₂
    Fluorine is the strongest oxidizing agent because it has the highest electronegativity and smallest atomic size.
  2. How does the reactivity of halogens with hydrogen vary?
    Answer:
    The reactivity of halogens with hydrogen decreases down the group:
    F₂ > Cl₂ > Br₂ > I₂
    Fluorine reacts explosively with hydrogen, while iodine reacts slowly. This variation is due to the decreasing bond strength of hydrogen-halogen bonds down the group.
  3. Why is the strength of HF different from HCl?
    Answer:
    HF is a weaker acid compared to HCl because of the strong hydrogen bonding in HF, which reduces its ability to dissociate completely in water. In contrast, HCl dissociates fully, making it a stronger acid.
  4. Write reactions of sulfuric acid with NaCl and NaBr.
    Answer:
    • With NaCl:
      NaCl+H2SO4→HCl+NaHSO4NaCl + H₂SO₄ → HCl + NaHSO₄
      Produces hydrogen chloride gas.
    • With NaBr:
      NaBr+H2SO4→HBr+NaHSO4NaBr + H₂SO₄ → HBr + NaHSO₄
      Further oxidation occurs, producing bromine gas.
  5. What is a disproportionation reaction?
    Answer:
    A disproportionation reaction is a redox reaction in which the same element is simultaneously oxidized and reduced.
    Example: Chlorine in water:
    Cl2+H2O→HCl+HOClCl₂ + H₂O → HCl + HOCl
  1. Explain the reactions of chlorine with sodium hydroxide.
    Answer:
    Chlorine reacts with NaOH to form a disproportionation reaction:
    2NaOH+Cl2→NaCl+NaClO+H2O2NaOH + Cl₂ → NaCl + NaClO + H₂O
    This forms sodium chloride and sodium hypochlorite, commonly used in bleach.
  2. Describe the silver nitrate test for halide ions.
    Answer:
    • Add dilute nitric acid to remove carbonate or hydroxide impurities.
    • Add silver nitrate solution.
      • Chlorides (Cl⁻): White precipitate (AgCl)
      • Bromides (Br⁻): Cream precipitate (AgBr)
      • Iodides (I⁻): Yellow precipitate (AgI)
  3. How does sulfuric acid react with halide ions?
    Answer:
    Sulfuric acid reacts differently with halides:
    • Cl⁻: Produces HCl gas.
    • Br⁻: Produces Br₂ and SO₂ due to redox reactions.
    • I⁻: Produces I₂ and H₂S due to stronger reduction.
  4. Compare the strength of halogen acids.
    Answer:
    The strength of halogen acids increases as the bond strength decreases:
    HF < HCl < HBr < HI
    HI is the strongest because the bond dissociation energy is the lowest.
  5. Evaluate the reactivity of halogens.
    Answer:
    Reactivity decreases down the group:
    F₂ > Cl₂ > Br₂ > I₂
    Fluorine reacts most vigorously due to its high electronegativity and small atomic radius.
  6. Discuss trends in:
  • Volatility of halogens: Decreases down the group due to increasing molecular size and van der Waals forces.
  • Strength in halogen molecules: Bond strength decreases down the group due to increasing bond length.
  1. Interpret the reactivity of halogens as oxidizing agents.
    Answer:
    Halogens are strong oxidizing agents because they gain electrons easily. Reactivity decreases as electronegativity and reduction potential decrease down the group.

Chapter 13: Environmental Chemistry – Air Exercise

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Environmental Chemistry air

Explore detailed solutions to Chapter 13: Environmental Chemistry – Air for Federal Board students. Includes multiple-choice answers, short and long questions with explanations on air pollution, greenhouse gases, acid rain, ozone depletion, and measures to reduce pollution. Perfect for exam preparation and understanding environmental chemistry concepts.

Multiple Choice Questions

(i) What is a primary source of air pollution?

  • Answer: (a) Fossil fuel combustion.
    Explanation: Burning fossil fuels releases harmful gases like CO₂, SO₂, and NOx, which significantly contribute to air pollution.

(ii) Which gas is primarily responsible for the greenhouse effect?

  • Answer: (c) Carbon dioxide (CO₂).
    Explanation: CO₂ traps heat in the Earth’s atmosphere, leading to global warming and climate change.

(iii) Nitrogen oxide (NO₂) is NOT a greenhouse gas.

  • Answer: (b) Water vapor (H₂O).
    Explanation: While water vapor acts as a greenhouse gas, its effect is considered natural and not directly linked to human activities.

(iv) Which is a major component of smog that poses risks to humans?

  • Answer: (a) Sulfur dioxide (SO₂).
    Explanation: Sulfur dioxide combines with other particles to form harmful smog, impacting respiratory health.

(v) Acid rain is primarily caused by the emission of:

  • Answer: (c) Sulfur dioxide (SO₂).
    Explanation: SO₂ reacts with water vapor in the atmosphere to form sulfuric acid, which falls to the ground as acid rain.

Short-Answer Questions

1. What is the difference between global warming and climate change?

  • Global warming refers to the rise in Earth’s average temperature due to increased levels of greenhouse gases like CO₂ and CH₄.
  • Climate change encompasses global warming and includes long-term changes in weather patterns, sea levels, and ecosystems caused by these temperature shifts.

2. Describe the health effects of air pollution.

  • Air pollution causes respiratory diseases like asthma and bronchitis.
  • It increases the risk of cardiovascular problems, lung cancer, and strokes.
  • Particulate matter (PM2.5) and toxic gases like SO₂ and NO₂ impair lung function and reduce life expectancy.

3. What are the major greenhouse gases, and how do they affect the Earth?

  • Major Greenhouse Gases:
    • Carbon dioxide (CO₂)
    • Methane (CH₄)
    • Nitrous oxide (N₂O)
    • Chlorofluorocarbons (CFCs)
  • Effects:
    • Trap heat in the atmosphere, increasing global temperatures.
    • Lead to melting glaciers, rising sea levels, and extreme weather events.

4. Define acid rain and its environmental impacts.

  • Definition: Acid rain forms when sulfur dioxide (SO₂) and nitrogen oxides (NOx) react with water vapor to form acidic compounds, which fall to the ground as precipitation.
  • Impacts:
    • Damages forests and crops by altering soil pH.
    • Harms aquatic ecosystems by increasing water acidity, killing fish and plants.
    • Erodes buildings and monuments, especially those made of limestone or marble.

5. What are some measures to reduce air pollution?

  • Shift to renewable energy sources like solar and wind power.
  • Use public transportation and reduce the use of private vehicles.
  • Promote afforestation and protect existing forests.
  • Implement stricter regulations for industries to reduce emissions of pollutants like CO₂, NO₂, and SO₂.

Long-Answer Questions

6. Discuss the role of environmental chemistry in addressing air pollution.
Environmental chemistry helps us understand the composition of air and the reactions occurring within the atmosphere. By studying pollutants like CO₂, SO₂, and NO₂, scientists can develop technologies such as scrubbers and catalytic converters to minimize emissions. Research in this field aids in crafting policies for cleaner air and reducing human impact on climate change.

7. Evaluate the causes and effects of ozone layer depletion.

  • Causes:
    • Release of chlorofluorocarbons (CFCs) from aerosols, refrigerants, and solvents.
    • UV light breaks CFCs into chlorine atoms, which destroy ozone molecules.
  • Effects:
    • Increased UV radiation reaching Earth, leading to skin cancer and cataracts in humans.
    • Harmful effects on marine ecosystems, particularly plankton.
    • Reduced crop yields and damage to plants due to UV exposure.

8. Suggest steps to minimize the harmful effects of air pollution on health and the environment.

  • Regularly monitor air quality and avoid outdoor activities during high pollution levels.
  • Switch to energy-efficient appliances and vehicles.
  • Promote recycling and reduce waste incineration.
  • Create awareness campaigns to educate the public on the dangers of air pollution and methods to combat it.

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