Learn Unit I: Chemical Substances - Nature and Behaviour with Free Lessons & Tips

4. Two important observations of the reaction are:
   • The mixture produces heat and generates steam, indicating an exothermic reaction.
   • The quicklime dissolves in water to form calcium hydroxide (slaked lime), accompanied by the release of heat and the formation of a milky white suspension.

The type of reaction taking place is a chemical reaction, specifically an exothermic reaction, in which quicklime (calcium oxide) reacts with water to form calcium hydroxide (slaked lime) and release heat.

Saturated hydrocarbons contain only single carbon-carbon bonds and are fully saturated with hydrogen atoms. An example is methane (CH4). Unsaturated hydrocarbons contain at least one carbon-carbon double or triple bond and may not be fully saturated with hydrogen atoms. An example is ethene (C2H4), which contains a carbon-carbon double bond.

• Catenation Property of Carbon: Carbon exhibits the property of catenation, which is the ability of an element to form covalent bonds with other atoms of the same element to form long chains or rings. This property is unique to carbon due to its small atomic size, intermediate electronegativity, and ability to form stable covalent bonds with itself through sp3 hybridization. Carbon atoms can form single, double, or triple bonds with each other, allowing for the formation of a wide variety of organic compounds with diverse structures and properties.

• Element A Burning with Golden Flame in Air and Reacting with Element B:

  • Element A is sodium (Na).
  • Element B with atomic number 17 is chlorine (Cl).
  • Product C is sodium chloride (NaCl).
  • Aqueous solution of C on electrolysis gives compound D, which is sodium hydroxide (NaOH), and liberates hydrogen gas (H2).
  • Reactions:
    • 2Na(s) + Cl2(g) → 2NaCl(s)
    • 2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g)

• Plaster of Paris is stored in a moisture-proof container because it is highly hygroscopic, meaning it readily absorbs moisture from the atmosphere. Exposure to moisture can cause Plaster of Paris to undergo premature setting or hardening, rendering it unusable. Storing it in a moisture-proof container helps to maintain its dryness and extend its shelf life.

• Mendeleev classified elements based on their atomic masses and chemical properties. He observed that elements with similar chemical properties occurred at regular intervals when arranged in order of increasing atomic mass. He used this periodicity to classify elements into rows (periods) and columns (groups) in his periodic table.

• Three points of difference between Mendeleev's Periodic Table and the Modern Periodic Table are:

  • Mendeleev's table was based on increasing atomic mass, while the modern periodic table is based on increasing atomic number.
  • Mendeleev left gaps in his table for undiscovered elements, while the modern table does not have gaps and accommodates all known elements.
  • Mendeleev's table did not accurately predict the properties of all elements, while the modern table provides a more accurate representation of element properties based on atomic structure and periodic trends.

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