Stoikiometri (4) | Menentukan Kadar Unsur dalam Senyawa | Kimia Kelas 11

Summary

In this educational video, the speaker explains the concept of stoichiometry, focusing on how to determine the mass and percent composition of elements in chemical compounds. Using practical examples, the speaker demonstrates how to calculate the mass of elements and their percentage in compounds like Fe2SO4, urea fertilizer, and MSG. The video breaks down complex calculations step by step, helping viewers understand the application of formulas to find the atomic mass and percent composition. The session concludes with helpful examples to reinforce the concepts, making it easier for 10th-grade chemistry students to grasp the topic.

Takeaways

• 😀 Stoichiometry is a concept in chemistry used to determine the level of an element in its compound.
• 😀 To find the mass of an element in a compound, use the formula: mass of element X = (number of atoms of X × atomic mass of X) ÷ molecular mass of compound × mass of compound.
• 😀 To find the percent composition of an element in a compound, use the formula: percent of element X = (number of atoms of X × atomic mass of X) ÷ molecular mass of compound × 100%.
• 😀 The first example demonstrates how to calculate the mass of iron in 4 grams of Fe2(SO4)3, which gives the result of 1.21 grams of iron.
• 😀 To calculate the molecular mass (MR) of Fe2(SO4)3, sum the individual atomic masses of its elements: Fe, S, and O, which results in an MR of 400.
• 😀 The second example calculates the mass percentage of nitrogen in urea fertilizer (CH4N2O), resulting in a 46.47% nitrogen content.
• 😀 To calculate the MR of urea (CH4N2O), you add the atomic masses of C, H, N, and O to get an MR of 60.
• 😀 The third example uses the formula for percentage composition to determine the number of nitrogen atoms in MSG (monosodium glutamate) with a nitrogen content of 9%.
• 😀 The result from the MSG example shows that the number of nitrogen atoms in each MSG molecule is approximately 1.
• 😀 The video provides a clear understanding of stoichiometry and how to apply formulas for mass and percent composition calculations in real-life examples.

Q & A

What is stoichiometry and how is it related to chemistry?

Stoichiometry is the study of the relationships between the amounts of reactants and products in chemical reactions. It helps in determining the quantities of substances involved in a chemical reaction, allowing us to calculate the mass or percentage of elements in compounds.

What formula is used to calculate the mass of an element in a compound?

To calculate the mass of an element in a compound, the formula is: Mass of element X = (Number of atoms of X × Atomic mass of X) / Molecular mass of compound × Mass of compound.

How do you calculate the percentage of an element in a compound?

To calculate the percentage of an element in a compound, use the formula: Percentage of element X = (Number of atoms of X × Atomic mass of X) / Molecular mass of compound × 100%.

In the example with Fe₂SO₄₃, how do you determine the mass of iron in the compound?

To find the mass of iron in Fe₂SO₄₃, you multiply the number of iron atoms (12) by the atomic mass of iron (56), divide by the molecular mass of Fe₂SO₄₃ (400), and then multiply by the total mass of the compound (4 grams). The result is 1.21 grams of iron.

What is the molecular mass (Mr) of Fe₂SO₄₃, and how is it calculated?

The molecular mass (Mr) of Fe₂SO₄₃ is calculated by adding the masses of all atoms in the compound: 2 × 56 (Fe) + 3 × 32 (S) + 12 × 16 (O) = 400 g/mol.

How do you calculate the mass percentage of nitrogen in urea fertilizer?

The mass percentage of nitrogen in urea (NH₂CONH₂) is calculated using the formula: Percentage of nitrogen = (Number of nitrogen atoms × Atomic mass of nitrogen) / Molecular mass of urea × 100%. For urea, this gives a result of 46.47% nitrogen content.

What are the steps to find the molecular mass of urea (NH₂CONH₂)?

To find the molecular mass of urea, you add the atomic masses of each element: 1 × 12 (C) + 1 × 16 (O) + 2 × 14 (N) + 4 × 1 (H) = 60 g/mol.

How is the nitrogen content in MSG calculated from its molecular composition?

The nitrogen content in MSG is calculated using the mass percentage formula. Given that MSG contains 9% nitrogen, the number of nitrogen atoms is calculated based on the mass percent and the molecular mass of MSG, resulting in one nitrogen atom per MSG molecule.

What is the molecular mass of MSG, and how does it help in finding the nitrogen atoms?

The molecular mass of MSG is 155 g/mol. Using this value, along with the given mass percentage of nitrogen (9%), we can calculate the number of nitrogen atoms in each molecule of MSG. The result shows that there is one nitrogen atom per molecule of MSG.

How do you simplify the calculations when finding the nitrogen atoms in MSG?

To simplify, divide the known values by common factors where possible. In this case, the mass percentage formula is simplified by cross-multiplying and reducing fractions, resulting in the answer that there is approximately one nitrogen atom in each MSG molecule.