Concentração das soluções​ ​- Química - Ensino Médio

Summary

In this Chemistry class, Professor Juliana Santiago explores the concept of concentration in solutions, focusing on common concentration and molar concentration. She explains how concentration reflects the relationship between solute and solvent, using an example of preparing a sodium hydroxide solution. The class covers both common concentration (mass of solute divided by volume of solution) and molar concentration (moles of solute per volume of solution). Professor Santiago also clarifies the difference between concentration and density, emphasizing the importance of understanding these concepts for real-world applications like health diagnostics and product packaging.

Takeaways

• 😀 Concentration of solutions is crucial in many fields, including health, cosmetics, food, and supplements.
• 😀 Concentration expresses the relationship between the mass or quantity of solute and the volume of the solution.
• 😀 A solution consists of two components: the solvent (greater quantity) and the solute (lesser quantity).
• 😀 Common concentration measures the mass of solute per volume of solution (g/L).
• 😀 Molar concentration (molarity) expresses the number of moles of solute per volume of solution (mol/L).
• 😀 A practical example: if you dissolve 20g of sodium hydroxide (NaOH) in 500mL of water, the common concentration is 40g/L.
• 😀 To find molarity, you first calculate the number of moles of solute using its molar mass (NaOH has a molar mass of 40g/mol).
• 😀 For molarity, the formula is: moles of solute / volume of solution in liters.
• 😀 In the example, 20g of NaOH (molar mass = 40g/mol) yields 0.5 moles, and the molarity is 1 mole/L.
• 😀 It's important not to confuse common concentration (mass/volume) with density (mass of solution/volume of solution).

Q & A

What is the definition of concentration in the context of solutions?

Concentration expresses the relationship between the mass or quantity of solute matter and the volume of the solution. It tells us how much solute is present in a given amount of solution.

Why is studying the concentration of solutions important?

Studying concentration helps in understanding the composition of solutions, which is crucial for various applications like diagnosing health conditions, analyzing food and cosmetics, and determining the effectiveness of drugs and supplements.

What is the difference between a solvent and a solute?

In a solution, the solvent is the substance present in the greater amount, while the solute is the substance in the lesser amount that dissolves in the solvent.

What are the two types of concentration focused on in this class?

The two types of concentration discussed are common concentration, which is based on the mass of the solute and volume of the solution, and molar concentration (molarity), which involves the number of moles of solute per volume of solution.

How do you calculate the common concentration of a solution?

Common concentration is calculated by dividing the mass of the solute (in grams) by the volume of the solution (in liters).

How is molar concentration (molarity) calculated?

Molarity is calculated by dividing the number of moles of solute by the volume of the solution (in liters). To find the number of moles, you divide the mass of the solute by its molar mass.

What is the molar mass of sodium hydroxide (NaOH)?

The molar mass of sodium hydroxide is 40 grams per mole. This is the sum of the atomic masses of sodium (23), oxygen (16), and hydrogen (1).

How do you calculate the number of moles of sodium hydroxide in the example provided?

The number of moles is calculated by dividing the mass of sodium hydroxide (20 grams) by its molar mass (40 grams per mole). This gives 0.5 moles of sodium hydroxide.

What is the molarity of the sodium hydroxide solution in the example?

The molarity is 1 mole per liter. This is calculated by dividing the number of moles (0.5) by the volume of the solution (0.5 liters).

What is the difference between common concentration and density?

Common concentration is the mass of solute divided by the volume of the solution, while density is the mass of the solution divided by the volume of the solution.