Tuesday, 10 December 2024

FOR CLASS 7 LANGUAGE OF CHEMISTRY

 

WORKSHEET 2  

 LANGUAGE OF CHEMISTRY

1. Fill in the Blanks

  1. The symbol of potassium is ____.
  2. The valency of nitrogen in ammonia (NH₃) is ____.
  3. The formula for calcium hydroxide is ____.
  4. A molecule of methane contains ____ carbon atom(s) and ____ hydrogen atom(s).
  5. The Latin name of sodium is ____.

2. True or False

  1. The symbol for lead is Pb. (True/False)
  2. The formula for sulfuric acid is H₂SO₃. (True/False)
  3. Oxygen exists as a diatomic molecule. (True/False)
  4. The chemical formula for zinc chloride is ZnCl₃. (True/False)
  5. The formula of baking soda is NaHCO₃. (True/False)

3. Short Answer Questions

  1. Write the chemical formula for:
    a. Ammonium chloride
    b. Aluminium oxide

  2. Define the following terms:
    a. Symbol
    b. Valency

  3. Explain how to determine the valency of an element from its atomic number.

  4. Write the balanced chemical equation for the reaction between hydrogen and chlorine to form hydrogen chloride.

  5. Differentiate between a molecule and a compound with suitable examples.

4. Long Answer Questions

  1. Explain the steps involved in balancing a chemical equation. Use the example of H₂ + O₂ → H₂O to illustrate your explanation.

  2. Describe the law of conservation of mass with an example of a chemical reaction. Also, explain why balancing equations is important in this context.

  3. Write the steps to derive the chemical formula of calcium nitrate. Include the valency and how the formula is written.

  4. Explain the difference between:
    a. Molecular formula and structural formula
    b. Atomic number and mass number

  5. List any five important chemical symbols and write their corresponding names, atomic numbers, and one use of each element in daily life.




ANSWERS

1. Fill in the Blanks

  1. K
  2. 3
  3. Ca(OH)₂
  4. 1, 4
  5. Natrium

2. True or False

  1. True
  2. False (The formula for sulfuric acid is H₂SO₄, not H₂SO₃.)
  3. True
  4. False (The formula for zinc chloride is ZnCl₂.)
  5. True

3. Short Answer Questions

a. NH₄Cl (Ammonium chloride)
b. Al₂O₃ (Aluminium oxide)

a. Symbol: A symbol is a shorthand representation of an element using one or two letters. For example, H represents hydrogen.
b. Valency: Valency is the combining capacity of an element, indicating the number of electrons an atom can lose, gain, or share to achieve a stable configuration.

  1. Valency Determination:
    The valency of an element is determined by the number of electrons in its outermost shell:
  • If it has 1–4 electrons, the valency equals that number.
  • If it has 5–7 electrons, the valency is (8 - number of outer electrons).
    Example: Carbon (atomic number 6) has 4 outer electrons, so its valency is 4.

  1. Balanced Equation:
    H₂ + Cl₂ → 2 HCl

  2. Difference Between Molecule and Compound:

  • Molecule: A molecule is a group of two or more atoms bonded together. It can be of the same element (e.g., O₂, H₂).
  • Compound: A compound is a substance formed when two or more different elements combine chemically (e.g., H₂O, CO₂).

4. Long Answer Questions

  1. Steps to Balance a Chemical Equation:
    a. Write the unbalanced equation: H₂ + O₂ → H₂O
    b. Count the number of atoms of each element on both sides.
    c. Adjust coefficients to balance the number of atoms for each element:

    • 2 H₂ + O₂ → 2 H₂O
      d. Check that the number of atoms on both sides is equal.
      e. Write the balanced equation: 2 H₂ + O₂ → 2 H₂O

  2. Law of Conservation of Mass:

  • Statement: Mass can neither be created nor destroyed in a chemical reaction.
  • Example: In the reaction 2 H₂ + O₂ → 2 H₂O, the mass of hydrogen and oxygen before and after the reaction remains the same.
  • Importance of Balancing: Balancing ensures the equation obeys the law of conservation of mass by equating the number of atoms on both sides.

  1. Steps to Derive the Formula for Calcium Nitrate:
    a. Calcium (Ca) has a valency of 2, and nitrate (NO₃) has a valency of 1.
    b. The formula is derived by crossing the valencies: Ca(NO₃)₂.
    c. Calcium nitrate contains one calcium ion and two nitrate ions.

  2. Differences:
    a. Molecular Formula vs Structural Formula:

    • Molecular formula shows the number and type of atoms in a molecule (e.g., H₂O).
    • Structural formula shows the arrangement of atoms in a molecule.
      b. Atomic Number vs Mass Number:
    • Atomic number is the number of protons in an atom's nucleus (e.g., Hydrogen = 1).
    • Mass number is the sum of protons and neutrons (e.g., Hydrogen = 1).

  3. Five Important Chemical Symbols:
     Symbol 

  • Element - H, Hydrogen 
  •  Atomic Number -1
  • Daily Use - Used in rocket fuel.
  • Element - O, Oxygen 
  •  Atomic Number -8
  • Daily Use - Essential for respiration..
  • Element -Fe Iron 
  •  Atomic Number -26 
  • Daily Use - Used in construction (steel).
  • Element -Na Sodium
  •  Atomic Number -11 
  • Daily Use - Found in table salt (NaCl). 
  • Element -C  Carbon 
  •  Atomic Number -6 
  • Daily Use - Found in fuels and organic compounds.


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