Perhitungan kimia/ stoikiometri- AIR KRISTAL

Introduction

This tutorial provides step-by-step guidance on stoichiometry focusing on calculating the percentage mass of water of crystallization and determining the amount of water in hydrated salts. These calculations are essential for understanding chemical compositions and reactions involving hydrates.

Step 1: Understanding Water of Crystallization

• Water of crystallization refers to the water molecules that are integrated into the crystal structure of a hydrated salt.
• It plays a crucial role in determining the properties and behavior of the salt.

Key Concepts

• Hydrated Salts: Salts that contain water molecules within their crystalline structure.
• Molar Mass: The mass of one mole of a substance, typically measured in grams per mole (g/mol).

Step 2: Calculating the Molar Mass of the Hydrated Salt

1. Identify the Formula: Write down the chemical formula of the hydrated salt (e.g., CuSO₄·5H₂O).

Calculate Molar Mass

• Find the molar mass of each component (cations, anions, and water).

For example, for CuSO₄·5H₂O

• Cu: 63.55 g/mol
• S: 32.07 g/mol
• O (from SO₄): 4 × 16.00 g/mol = 64.00 g/mol
• H₂O: 5 × (2 × 1.01 g/mol + 16.00 g/mol) = 90.10 g/mol

Add them together

• Total = 63.55 + 32.07 + 64.00 + 90.10 = 249.72 g/mol

Step 3: Calculating the Percentage Mass of Water of Crystallization

Use the Molar Mass

• Determine the total mass of water in the hydrated salt (e.g., 90.10 g/mol for 5H₂O).

Calculate Percentage

Use the formula

[ \text{Percentage of Water} = \left( \frac{\text{Mass of Water}}{\text{Molar Mass of Hydrated Salt}} \right) \times 100 ]

For CuSO₄·5H₂O

[ \text{Percentage of Water} = \left( \frac{90.10}{249.72} \right) \times 100 \approx 36.1% ]

Step 4: Determining the Amount of Water in a Given Mass of Hydrated Salt

Calculate the Mass of Water

• If you have a specific mass of the hydrated salt (e.g., 200 g of CuSO₄·5H₂O), use the previously calculated percentage.

Use the Formula

Calculate the mass of water

[ \text{Mass of Water} = \left( \text{Mass of Hydrated Salt} \times \frac{\text{Percentage of Water}}{100} \right) ]

Example

[ \text{Mass of Water} = 200 \times \frac{36.1}{100} \approx 72.2 \text{ g} ]

Conclusion

In this tutorial, we covered how to calculate the percentage mass of water of crystallization and how to determine the amount of water in hydrated salts. Mastering these calculations is vital for chemistry students, especially when dealing with stoichiometry. For further practice, try calculating these values for different hydrated salts and explore their real-world applications, such as in pharmaceuticals and materials science.