Class 9th · Chemistry · Chapter 4
Chapter 4: Stoichiometry
Chapter 4 of the Punjab Board Class 9th Chemistry textbook runs from page 56 to 70. Open any of those pages in GenZ Books, tap a question, and the answer is worked from this chapter.
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A sample answer from GenZ Books
Solve · page 60: Empirical formula of a compound is CH. Its molecular mass is 78 g mol". Find out its molecular formula.
Given: Empirical formula (ایمپیریکل فارمولا) = $\text{CH}$ Molecular mass (مالیکیولر ماس) = $78\text{ g mol}^{-1}$
Find: Molecular formula (مالیکیولر فارمولا)
Formula: $$\text{Empirical formula mass} = \text{Sum of atomic masses of all atoms in the empirical formula}$$ $$n = \frac{\text{Molecular mass}}{\text{Empirical formula mass}}$$ $$\text{Molecular formula} = (\text{Empirical formula})_n$$
Solution:
- Calculate the empirical formula mass of $\text{CH}$ using the atomic masses of Carbon ($\text{C} = 12\text{ g mol}^{-1}$) and Hydrogen ($\text{H} = 1\text{ g mol}^{-1}$):
$$\text{Empirical formula mass} = 12\text{ g mol}^{-1} + 1\text{ g mol}^{-1}$$ $$\text{Empirical formula mass} = 13\text{ g mol}^{-1}$$
- Find the value of $n$:
$$n = \frac{78\text{ g mol}^{-1}}{13\text{ g mol}^{-1}}$$ $$n = 6$$
- Determine the molecular formula:
$$\text{Molecular formula} = (\text{CH})_6$$ $$\text{Molecular formula} = \text{C}_{6}\text{H}_{6}$$
Answer: $\text{C}_{6}\text{H}_{6}$
AI-generated from the chapter text by GenZ Books. It can make mistakes — check it against your textbook and your teacher.