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

Summary

In this video, the instructor teaches 10th-grade chemistry students about stoichiometry, focusing on how to determine empirical and molecular formulas through chemical calculations. The process includes finding the empirical formula by calculating the smallest atomic ratios and using molar masses, followed by determining the molecular formula using the empirical formula and molecular weight. Through practical examples involving compounds like carbon, hydrogen, oxygen, and nitrogen, the video walks viewers through the steps and formulas required to solve stoichiometric problems, ensuring a clear understanding of key concepts.

Takeaways

• 😀 Stoichiometry helps us determine the chemical formula of compounds by analyzing their composition.
• 😀 The empirical formula represents the simplest whole-number ratio of elements in a compound.
• 😀 To find the empirical formula, first calculate the moles of each element by dividing mass by atomic mass.
• 😀 After finding the moles, simplify the ratio of moles of each element to determine the empirical formula.
• 😀 The molecular formula shows the exact number of atoms of each element in one molecule of the compound.
• 😀 To find the molecular formula, first calculate the empirical formula and then compare its molar mass to the molecular mass of the compound.
• 😀 The ratio (n) between the molar masses of the molecular and empirical formulas helps calculate the molecular formula.
• 😀 Example 1: Given 2.4 g of carbon, 0.4 g of hydrogen, and 3.2 g of oxygen, the empirical formula is CH2O.
• 😀 In Example 1, the molecular formula of the compound is C2H4O2, as the molar mass of the molecular compound is twice that of the empirical formula.
• 😀 Example 2: A compound with 60% carbon, 5% hydrogen, and 35% nitrogen leads to the empirical formula C2H2N.
• 😀 Example 3: Given 300 grams of a compound and Avogadro's number, we determine the molecular formula C6H12O6 from the empirical formula CH2O.

Q & A

What is the empirical formula of a compound?

The empirical formula represents the simplest whole-number ratio of elements in a compound.

How do you determine the empirical formula of a compound?

To determine the empirical formula, first find the mass or percentage of each element in the compound. Then, divide each element's mass or percentage by its atomic mass to find the number of moles. Finally, determine the simplest whole-number ratio of the moles.

In the first example, how do you calculate the moles of each element?

For Carbon (C), divide 2.4g by 12 (atomic mass of C). For Hydrogen (H), divide 0.4g by 1 (atomic mass of H). For Oxygen (O), divide 3.2g by 16 (atomic mass of O). This gives the respective moles: 0.2 for C, 0.4 for H, and 0.2 for O.

What does the ratio of moles indicate in the empirical formula?

The ratio of moles represents the indices of each atom in the empirical formula. For example, if the ratio is 1 : 2 : 1 for C : H : O, the empirical formula would be CH₂O.

What is the molecular formula of a compound?

The molecular formula gives the exact number of atoms of each element in a molecule of the compound.

How do you determine the molecular formula of a compound?

To determine the molecular formula, first find the empirical formula. Then, calculate the molecular mass (Mr) and compare it with the empirical formula mass. Divide the molecular mass by the empirical formula mass to find 'n'. Finally, multiply the empirical formula by 'n' to get the molecular formula.

How do you calculate the molecular formula for a compound with a known empirical formula and molecular mass?

First, calculate the empirical formula mass. Then, divide the known molecular mass by the empirical formula mass to get 'n'. Finally, multiply the empirical formula by 'n' to obtain the molecular formula.

In Example 1, how is the molecular formula determined for CH₂O with a molecular mass of 60?

The empirical formula is CH₂O with an empirical formula mass of 30. The molecular mass is 60. Divide 60 by 30 to get n = 2. Multiply the empirical formula by 2 to get the molecular formula C₂H₄O₂.

How is the empirical formula of pyrimidine determined from the given percentages?

For pyrimidine, given the percentages of C (60%), H (5%), and N (35%), calculate the moles of each element by dividing the percentage by the atomic mass: C (60 ÷ 12 = 5), H (5 ÷ 1 = 5), N (35 ÷ 14 = 2.5). Simplify the ratio to get C : H : N = 2 : 2 : 1. The empirical formula is C₂H₂N.

What is the molecular formula for a compound with empirical formula CH₂O, a mass of 300g, and 10²⁴ molecules?

To calculate the molecular formula, first find the molecular mass using Avogadro’s number. The molecular mass (Mr) is 180. Divide the molecular mass (180) by the empirical formula mass (30) to get n = 6. Multiply the empirical formula CH₂O by 6 to obtain the molecular formula C₆H₁₂O₆.