Stoikiometri (3) | Menentukan Rumus Empiris Dan Rumus Molekul | Kimia Kelas 10

Introduction

In this tutorial, we will explore the concepts of empirical and molecular formulas in stoichiometry, a fundamental topic in chemistry for 10th-grade students. Understanding how to calculate these formulas is essential for determining the composition of chemical compounds and their reactions.

Step 1: Understanding Empirical Formulas

Empirical formulas represent the simplest whole-number ratio of atoms in a compound. To determine the empirical formula, follow these steps:

1. Determine the Mass of Each Element:

   • If given in a problem, note the mass of each element present in the compound.
   • If starting from a molecular formula, convert the molecular weights to grams.

2. Convert Mass to Moles:

   Use the formula

   [ \text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}} ]
   • Calculate the number of moles for each element.

3. Find the Simplest Ratio:

   • Divide each mole value by the smallest number of moles calculated.
   • Round off to the nearest whole number if necessary to get the ratio of atoms.

4. Write the Empirical Formula:

   • Use the ratio from the previous step to write the empirical formula, indicating the number of each type of atom present.

Step 2: Understanding Molecular Formulas

Molecular formulas give the actual number of atoms of each element in a molecule. Here’s how to calculate it:

1. Find the Empirical Formula:

   • Start by determining the empirical formula as outlined in Step 1.

2. Calculate the Molar Mass of the Empirical Formula:

   • Sum the atomic masses of all the elements in the empirical formula.

3. Determine the Molecular Mass:

   • If provided, use the molecular mass of the compound given in the problem.

4. Calculate the Ratio of Molecular to Empirical Mass:

   Use the formula

   [ n = \frac{\text{Molecular Mass}}{\text{Empirical Mass}} ]
   • This gives the number of empirical units in one molecular unit.

5. Write the Molecular Formula:

   • Multiply the subscripts in the empirical formula by ( n ) to obtain the molecular formula.

Step 3: Practical Examples

To solidify your understanding, consider working through some examples:

• Example for Empirical Formula:

  Given a compound with 12g of Carbon (C) and 32g of Oxygen (O)

  • Calculate moles of C: ( \frac{12g}{12g/mol} = 1 ) mol
  • Calculate moles of O: ( \frac{32g}{16g/mol} = 2 ) mol
  • The simplest ratio is 1:2, so the empirical formula is CO₂.

• Example for Molecular Formula:

  If the empirical formula is CO₂ and the molar mass of the compound is 88 g/mol

  • Molar mass of CO₂ = 12 + (2 x 16) = 44 g/mol
  • ( n = \frac{88g/mol}{44g/mol} = 2 )
  • The molecular formula is C₂O₄.

Conclusion

In this tutorial, we covered the essential steps to determine empirical and molecular formulas in stoichiometry. By understanding these concepts, you can analyze chemical compounds effectively. For further practice, try working through additional examples or problems involving different compounds to deepen your comprehension.