Molarity | Intermolecular forces and properties | AP Chemistry | Khan Academy

TL;DR

Molarity measures the concentration of a solute in a solution, calculated by dividing the number of moles of solute by the liters of solution.

Transcript

• [Instructor] In this video, we're gonna talk about one of the most common ways to measure solute concentration in a solution. And that is molarity. And molarity is defined as the number of moles of solute, the thing that we are dissolving in a solvent, that divided by the liters of solution. So let's just do an example and see if we can calculate... Read More

Key Insights

• ❓ Molarity is a commonly used method to measure solute concentration in a solution.
• 🗂️ The formula for molarity is the number of moles of solute divided by the liters of solution.
• 💆 The molar mass of a substance is used to convert grams of solute to moles.
• 🛝 Rounding the molarity to the appropriate number of significant figures is essential for accuracy.

Questions & Answers

Q: What is molarity and how is it calculated?

Molarity is a measure of solute concentration in a solution. It is calculated by dividing the number of moles of solute by the liters of solution.

Q: How do you calculate the number of moles of solute?

To calculate the number of moles of solute, divide the mass of the solute by its molar mass. In the example given, 35.5 grams of sodium sulfate is divided by its molar mass of 142.04 g/mol.

Q: What is the significance of rounding the molarity to three significant figures?

Rounding the molarity to three significant figures ensures that the calculated value is accurate and precise. In the example, the rounded molarity is 1.00 M.

Q: What does the "M" symbol stand for in molarity?

The "M" symbol represents molarity, which indicates the number of moles of solute per liter of solution. It is the unit used to express molarity.

Summary & Key Takeaways

• Molarity is a common way to measure solute concentration in a solution.

• It is calculated by dividing the number of moles of solute by the liters of solution.

• In an example, 35.5 grams of sodium sulfate are dissolved in water to create a solution, and the molarity is calculated to be 1.00 M.