solved chemistry exercises

State of matter and phase changes new book slo base exercise solved

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solved exercises based on the new SLO (Student Learning Outcomes) syllabus for “State of Matter and Phase Changes.” This comprehensive guide includes detailed solutions, simple explanations, and key concepts to help students master the topic effectively.

(i) Matter is present in neon signs in the state of:

  • Options: (a) Supercritical fluid
    (b) Plasma
    (c) Gas
    (d) Liquid crystal
  • Correct Answer: (b) Plasma
  • Explanation:
    Neon signs operate by ionizing neon gas with electricity. This ionization creates plasma, a state of matter consisting of freely moving electrons and ions that emit light.

(ii) Hazardous effects of shopping bags are studied in:

  • Options: (a) Geochemistry
    (b) Inorganic chemistry
    (c) Analytical Chemistry
    (d) Environmental Chemistry
  • Correct Answer: (d) Environmental Chemistry
  • Explanation:
    Environmental chemistry studies chemical processes in the environment, including pollution and the non-biodegradability of plastic shopping bags.

(iii) The man-made polymer is:

  • Options: (a) Starch
    (b) Polystyrene
    (c) Protein
    (d) Cellulose
  • Correct Answer: (b) Polystyrene
  • Explanation:
    Polystyrene is a synthetic polymer used in packaging materials. Starch and cellulose are natural biopolymers, and protein is a natural macromolecule.

(iv) The allotropic form of sulfur is:

  • Options: (a) Brass
    (b) Rhombic
    (c) Graphite
    (d) Bronze
  • Correct Answer: (b) Rhombic
  • Explanation:
    Rhombic sulfur is the most stable crystalline form of sulfur. Brass and bronze are alloys, and graphite is an allotrope of carbon.

(v) Which liquid among the following is a colloidal solution?

  • Options: (a) Milk
    (b) Slaked lime used for whitewash
    (c) Vinegar solution
    (d) Mixture of AgCl in water
  • Correct Answer: (a) Milk
  • Explanation:
    Milk is a colloid where fat droplets are dispersed in water. Slaked lime is a suspension, vinegar is a true solution, and AgCl forms a precipitate in water.

(vi) Which of the following is a heterogeneous mixture?

  • Options: (a) A solution of calcium in hydroxide water
    (b) A solution of potassium nitrate in water
    (c) Hot chocolate
    (d) Concrete mixture
  • Correct Answer: (d) Concrete mixture
  • Explanation:
    Heterogeneous mixtures have non-uniform compositions. Concrete is an example, with distinct phases of sand, cement, and water. The other options are homogeneous mixtures.

(vii) A state of matter whose properties are between those of liquids and crystalline solids:

  • Options: (a) Liquid crystal
    (b) Supercritical fluid
    (c) Plasma
    (d) Dark matter
  • Correct Answer: (a) Liquid crystal
  • Explanation:
    Liquid crystals have properties of both liquids (flow) and solids (ordered molecular structure). They are commonly used in LCDs.

(viii) When the tiny particles of a substance are dispersed through a medium, the mixture is named as:

  • Options: (a) True solution
    (b) Colloid
    (c) Suspension
    (d) Heterogeneous mixture
  • Correct Answer: (b) Colloid
  • Explanation:
    A colloid is a mixture where particles are small enough to stay dispersed and not settle, like in milk or fog. Suspensions have larger particles that settle, and true solutions are homogeneous.

(ix) A solution of KClO3 has a solubility of about 13.2g per 100 cm³ at 40∘C. How will its solubility be affected if you decrease the temperature?


Options:
(a) The solubility will increase.
(b) The solubility will decrease.
(c) The solubility will remain the same.
(d) The solubility will first increase with temperature and then it will decrease.

Correct Answer: (b) The solubility will decrease.
Explanation: Solubility of most solid solutes, such as KClO3, decreases with a decrease in temperature because solubility depends on the kinetic energy of particles, which is reduced at lower temperatures.

(x) You are studying the rate of hydrolysis of organic compound starch under different conditions of temperature. In which branch of chemistry will this topic fall?


Options:
(a) Organic Chemistry
(b) Analytical Chemistry
(c) Biochemistry
(d) Physical Chemistry

Correct Answer: (d) Physical Chemistry
Explanation: Physical chemistry deals with studying the rate of chemical reactions and how external factors, such as temperature, influence these reactions. Hydrolysis of starch involves the study of reaction rates under physical conditions.

Short Answer Questions

1. Why is there a need to divide Chemistry into many branches? Give three reasons.
Answer: Chemistry is divided into branches to make it easier to study and apply:

  1. Specialization: Each branch focuses on a specific area, like organic chemistry studies carbon compounds, while analytical chemistry deals with testing and measurements.
  2. Understanding Complexity: Different chemical reactions and processes are complex and require specialized study.
  3. Practical Applications: Dividing chemistry allows us to apply knowledge to specific fields, such as medicine (biochemistry) or materials science (physical chemistry).

2. Reactions may take place due to electrons outside the nucleus or inside the nucleus. Which branches of chemistry cover these two types of reactions?
Answer:

  1. Electron-based reactions: These are covered in branches like organic and inorganic chemistry. They involve the sharing or transfer of electrons.
  2. Nuclear-based reactions: These are covered in nuclear chemistry, which studies changes within the nucleus, such as radioactive decay or fission.

3. What types of problems are solved in analytical chemistry?
Answer: Analytical chemistry solves problems related to:

  • Identifying the composition of unknown substances.
  • Determining the concentration of specific chemicals in a sample.
  • Monitoring the quality and purity of materials in industries.

4. Both graphite and graphene have hexagonal layered structures. What is the difference?
Answer:

  • Graphite: Consists of multiple layers of carbon atoms arranged in hexagonal structures. The layers are weakly bonded, making graphite soft and slippery.
  • Graphene: Consists of a single layer of carbon atoms in a hexagonal structure. It is stronger, more conductive, and lightweight compared to graphite.

5. Why are supercritical fluids important?
Answer: Supercritical fluids (like carbon dioxide at high pressure) are important because:

  • They are used as solvents in chemical processes.
  • They allow for efficient extraction of compounds (e.g., caffeine from coffee).
  • They are environmentally friendly compared to conventional solvents.

6. In which state does matter exist in the Sun?
Answer: Matter in the Sun exists in the plasma state, where atoms are ionized into positive ions and free electrons due to extremely high temperatures.

7. What is the importance of graphene?
Answer: Graphene is important because it:

  • Has excellent electrical conductivity, making it useful in electronics.
  • Is extremely strong yet lightweight, used in materials science.
  • Has potential applications in energy storage, sensors, and medicine.

8. Which form of matter do most of the material things in this world belong to?
Answer: Most materials in the world are in the solid state, where atoms are tightly packed and maintain a fixed shape.

Constructed Response Questions

1. How does a supercritical state look like?
Answer: A supercritical state is a phase where a substance behaves like both a gas and a liquid. It has no distinct boundary between liquid and gas phases and is often clear and dense, like a thick gas.

2. In what way is plasma created in a fluorescent tube?
Answer: In a fluorescent tube:

  • Electric current flows through low-pressure gas (like mercury vapor).
  • The energy excites the gas atoms, ionizing them into plasma, emitting ultraviolet light.
  • This UV light interacts with the phosphor coating inside the tube, producing visible light.

3. Most of the molecules we study in biochemistry are organic in nature. Where does the difference exist in organic and biochemistry branches of chemistry?
Answer:

  • Organic Chemistry: Focuses on all carbon-containing compounds, whether living or non-living.
  • Biochemistry: Studies chemical processes and compounds specific to living organisms, like enzymes and DNA.

4. Give the reason for the brilliance shown by a diamond. Can you improve it?
Answer: Diamonds show brilliance because:

  • They have a high refractive index, bending light multiple times inside the crystal.
  • Light reflects and refracts, creating sparkle.
    Improvement: Brilliance can be enhanced by cutting the diamond precisely to optimize light reflection.

5. Explain the dissolution of NaCl in water.
Answer:
When NaCl dissolves in water:

  • Water molecules surround Na⁺ and Cl⁻ ions due to their polarity.
  • The positive side of water (H⁺) attracts Cl⁻ ions, and the negative side (O⁻) attracts Na⁺ ions.
  • These ions are separated and evenly distributed in the water, forming a solution.

Short Questions

6. Why do different compounds have different solubilities in water at a particular temperature?
Answer: Different compounds have different solubilities because:

  • Their molecular structures and forces vary (ionic, covalent, or hydrogen bonding).
  • The temperature affects how much energy is available to break bonds between molecules.
  • The nature of the solvent (like water being polar) interacts differently with solutes.

7. Why can NaCl be crystallized from water just like KNO3?
Answer: Both NaCl and KNO3 dissolve in water to form a solution. By cooling the solution or evaporating water, the solubility decreases, and the ions come together to form crystals.

8. Why is graphite slippery to touch? What property of graphite enables it to be used as a lubricant?
Answer:

  • Graphite is slippery because its carbon atoms form layers that slide over each other easily due to weak forces between them.
  • This property makes it an excellent lubricant, reducing friction in machinery.

Descriptive Questions

1. Mention the branch of Chemistry for each topic:
(a) Rate of a reaction: Physical Chemistry (studies reaction rates and factors affecting them).
(b) Digestion of food in the human body: Biochemistry (focuses on chemical processes in living organisms).
(c) Properties of plasma: Physical Chemistry (examines the fourth state of matter).
(d) Ecosystem: Environmental Chemistry (studies the chemical processes affecting ecosystems).
(e) Reactions during fireworks: Inorganic Chemistry (explains reactions involving metals and salts).
(f) Measurement of absorption of wavelengths: Analytical Chemistry (focuses on spectroscopic techniques).

2. What are allotropic forms? Explain the allotropic forms of carbon and sulfur. How does coal differ from diamond?
Answer:

  • Allotropes: Different physical forms of the same element, having different structures.
  • Carbon Allotropes:
    • Diamond: Hard, transparent, with a 3D rigid structure.
    • Graphite: Soft, slippery, made of layers.
    • Fullerene: Spherical molecules (like a ball).
  • Sulfur Allotropes:
    • Rhombic Sulfur: Solid at room temperature.
    • Monoclinic Sulfur: Forms at higher temperatures.
  • Coal vs. Diamond:
    • Coal: Impure, made of carbon with other substances.
    • Diamond: Pure carbon in a crystalline form with strong covalent bonds.

3. What are supercritical fluids? How are they different from ordinary liquids?
Answer:

  • Supercritical Fluids: Substances at a temperature and pressure where they have properties of both gases and liquids.
  • Difference:
    • Supercritical fluids are denser than gases but flow like liquids.
    • They are used as solvents (e.g., in caffeine extraction).

4. Define solubility of a solute. How does the solubility of solutes change with temperature?
Answer:

  • Solubility: The maximum amount of solute that can dissolve in a solvent at a specific temperature.
  • Effect of Temperature:
    • For solids: Solubility increases with temperature.
    • For gases: Solubility decreases as temperature rises.

5. What types of movements are present in gaseous and liquid molecules?
Answer:

  • Gases: Molecules move freely in all directions with high speed (random motion).
  • Liquids: Molecules move slower than gases and can slide past each other (flow).

6. Differentiate between inorganic and organic chemistry.
Answer:

  • Organic Chemistry: Studies compounds containing carbon (e.g., fuels, plastics).
  • Inorganic Chemistry: Studies compounds without carbon (e.g., salts, metals).

Investigative Questions

1. Describe the process in which potassium nitrate is purified by crystallizing it in water.
Answer:

  1. Dissolve KNO3 in hot water to make a saturated solution.
  2. Filter the solution to remove impurities.
  3. Allow the solution to cool slowly.
  4. KNO3 crystals form as the solubility decreases.
  5. Separate the crystals and dry them.

2. Graphene is called a miracle material. Which of its properties makes it very useful in electronics?
Answer:
Graphene is highly useful in electronics because:

  • It is an excellent conductor of electricity.
  • It is extremely thin and lightweight.
  • It has high flexibility and strength, making it ideal for advanced devices like flexible screens and super-fast processors.

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