How Many Moles Of K2so4 Are In 15.0g Of K2so4

How Many Moles of K₂SO₄ Are in 15.0g of K₂SO₄? A Comprehensive Guide

Determining the number of moles in a given mass of a substance is a fundamental concept in chemistry. This calculation is crucial for various applications, from stoichiometry problems to understanding solution concentrations. This article will walk you through the step-by-step process of calculating the number of moles of potassium sulfate (K₂SO₄) present in 15.0g of K₂SO₄, explaining the underlying principles and providing practical tips for similar calculations.

Understanding Moles and Molar Mass

Before diving into the calculation, let's clarify the key concepts:

What is a Mole?

A mole (mol) is the International System of Units (SI) base unit for the amount of substance. It represents a specific number of entities, whether atoms, molecules, ions, or other specified particles. This number is known as Avogadro's number, approximately 6.022 x 10²³. One mole of any substance contains Avogadro's number of particles.

What is Molar Mass?

Molar mass is the mass of one mole of a substance. It's expressed in grams per mole (g/mol). For elements, the molar mass is numerically equal to the atomic mass found on the periodic table. For compounds, the molar mass is the sum of the molar masses of all the atoms in the chemical formula.

Calculating the Molar Mass of K₂SO₄

To calculate the number of moles in 15.0g of K₂SO₄, we first need to determine its molar mass. We'll use the atomic masses from the periodic table:

• Potassium (K): Approximately 39.10 g/mol
• Sulfur (S): Approximately 32.07 g/mol
• Oxygen (O): Approximately 16.00 g/mol

K₂SO₄ contains:

• 2 potassium atoms (2 * 39.10 g/mol = 78.20 g/mol)
• 1 sulfur atom (1 * 32.07 g/mol = 32.07 g/mol)
• 4 oxygen atoms (4 * 16.00 g/mol = 64.00 g/mol)

Therefore, the molar mass of K₂SO₄ is: 78.20 g/mol + 32.07 g/mol + 64.00 g/mol = 174.27 g/mol

Calculating Moles of K₂SO₄ in 15.0g

Now that we know the molar mass of K₂SO₄, we can calculate the number of moles in 15.0g using the following formula:

Moles = Mass (g) / Molar Mass (g/mol)

Plugging in the values:

Moles = 15.0 g / 174.27 g/mol = 0.0860 moles

Therefore, there are approximately 0.0860 moles of K₂SO₄ in 15.0g of K₂SO₄.

Significant Figures and Precision

It's crucial to pay attention to significant figures throughout the calculation. The given mass (15.0g) has three significant figures. The atomic masses used are also given to varying degrees of precision, typically four. Therefore, our final answer should also have three significant figures, which is why we report 0.0860 moles instead of a more precise, but less accurate, value.

Practical Applications and Extensions

Understanding mole calculations is essential for various chemical applications, including:

Stoichiometry:

Stoichiometry deals with the quantitative relationships between reactants and products in chemical reactions. Knowing the number of moles of a reactant allows you to calculate the amount of product formed or the amount of other reactants needed.

Solution Chemistry:

Molarity, a common unit of concentration, is defined as the number of moles of solute per liter of solution. Calculating the number of moles is the first step in determining the molarity of a solution.

Titration Calculations:

Titration involves determining the concentration of a solution by reacting it with a solution of known concentration. Mole calculations are crucial for interpreting titration data and determining the unknown concentration.

Troubleshooting Common Mistakes

Here are some common mistakes to avoid when performing mole calculations:

• Incorrect Molar Mass: Double-check the atomic masses from a reliable periodic table and ensure you've correctly calculated the molar mass of the compound.
• Unit Errors: Make sure your units are consistent. Use grams for mass and g/mol for molar mass.
• Significant Figures: Pay close attention to significant figures throughout the calculation to maintain accuracy in your final answer.
• Misinterpreting the Problem: Carefully read the problem statement to ensure you're calculating the correct quantity.

Further Exploration: Working with Hydrates

Some compounds exist as hydrates, meaning they contain water molecules incorporated into their crystal structure. For example, copper(II) sulfate pentahydrate (CuSO₄·5H₂O) contains five water molecules per formula unit. When calculating the molar mass of a hydrate, you must include the mass of the water molecules.

Example: Let's say you have 10.0g of CuSO₄·5H₂O. To calculate the number of moles, you would first calculate the molar mass of CuSO₄·5H₂O, including the mass of the five water molecules, and then use the same formula as before (Moles = Mass/Molar Mass).

Conclusion

Calculating the number of moles in a given mass of a substance is a fundamental skill in chemistry. By understanding the concept of moles, molar mass, and following the step-by-step procedure outlined in this article, you can accurately perform these calculations for various applications. Remember to pay attention to significant figures and double-check your work to avoid common errors. With practice, these calculations will become second nature, empowering you to tackle more complex chemical problems. This thorough understanding provides a strong foundation for further exploration into the fascinating world of chemistry and its applications.