CHAPTER 2 Matter and Atoms 2.3 Mixtures and Solutions

A recipe calls for you to “mix until homogeneous.” What does that mean? Encourage students to come up with their own definition for “homogeneous.” The chemical definition comes up in the next slide.

A mixture that is uniform throughout.

Different samples may have different compositions. A mixture that is uniform throughout. Different samples may have different compositions.

What happens when sugar is added to water? Molecules of solvent (usually water) collide with and transfer energy to solute (sugar) molecules.

What happens when sugar is added to water? A solution is obtained.

Is orange juice a solution? As stated in the next slide, students should find that some things like sugar are dissolved, while pulp is not. It is partially a solution. Hint: Are things dissolved in orange juice?

Is orange juice a solution? It is partially a solution because some chemicals are dissolved in water, but some bits (like pulp) are not.

These four solutions contain the same solvent and solute. Which one is the most concentrated solution? Which one is the most dilute solution?

concentration: the amount of each solute compared to the total solution.

Variables Can you dissolve salt in water? Amount of salt Amount of water Can you dissolve salt in water? The answer to that question would be “yes.”

Variables Can you dissolve salt in water? Can you continue adding more and more salt, and still get a solution? Amount of salt Amount of water The correct answer is “no,” because at some point, some salt will sit at the bottom of the container.

Variables Can you dissolve salt in water? Can you continue adding more and more salt, and still get a solution? Can you dissolve more salt when you increase the temperature? Amount of salt Amount of water Amount of salt Amount of water Temperature Intuition would suggest that the answer is (correctly) “yes.” This exercise is to help students think of everyday life’s observations.

Solubility of common substances in water at 25oC solubility: the amount of a solute that will dissolve in a particular solvent at a particular temperature and pressure.

If the concentration of a sugar solution is 75 g/L, how much solution do you need if you want 10 g of sugar?

If the concentration of a sugar solution is 75 g/L, how much solution do you need if you want 10 g of sugar? Asked: Volume of solution Given: 10 g of solute and concentration of 75 g/L Relationships:

If the concentration of a sugar solution is 75 g/L, how much solution do you need if you want 10 g of sugar? Asked: Volume of solution Given: 10 g of solute and concentration of 75 g/L Relationships: Solve: 1 L = 1,000 mL so 0.133 L = 133 mL

How much menthol do you need to make 10 kg of mouthwash if the concentration of menthol must be 0.05%?

How much menthol do you need to make 10 kg of mouthwash if the concentration of menthol must be 0.05%? Asked: Mass of solute Given: 10 kg of solution, solute concentration of 0.05% Relationships:

How much menthol do you need to make 10 kg of mouthwash if the concentration of menthol must be 0.05%? Asked: Mass of solute Given: 10 kg of solution, solute concentration of 0.05% Relationships: Solve:

molarity: the number of moles of solute per liter of solution.

If 10.0 g of citric acid (C6H8O7) is added to 500 mL of water, what is the molarity of the resulting solution?

If 10.0 g of citric acid (C6H8O7) is added to 500 mL of water, what is the molarity of the resulting solution? Asked: The molarity of a solution Given: The amount of solute (citric acid) and the volume of solution Relationships:

If 10.0 g of citric acid (C6H8O7) is added to 500 mL of water, what is the molarity of the resulting solution? Asked: The molarity of a solution Given: The amount of solute (citric acid) and the volume of solution Relationships: Solve: Start by calculating the formula mass of C6H8O7:

If 10.0 g of citric acid (C6H8O7) is added to 500 mL of water, what is the molarity of the resulting solution? Asked: The molarity of a solution Given: The amount of solute (citric acid) and the volume of solution Relationships: Solve: Start by calculating the formula mass of C6H8O7: Next we calculate the number of moles in 10.0 g of C6H8O7:

If 10.0 g of citric acid (C6H8O7) is added to 500 mL of water, what is the molarity of the resulting solution? Asked: The molarity of a solution Given: The amount of solute (citric acid) and the volume of solution Relationships: Solve: Start by calculating the formula mass of C6H8O7: Next we calculate the number of moles in 10.0 g of C6H8O7: Answer:

Ascorbic acid = Vitamin C Vitamin C acts as a food preservative by reacting with oxygen (O2) Ascorbic acid C6H8O6

How much (volume) of a 1 M ascorbic acid solution will completely react with 0.02 moles of oxygen (O2)?

How much (volume) of a 1 M ascorbic acid solution will completely react with 0.02 moles of oxygen (O2)? Asked: Volume of solution Given: Concentration (1M) and balanced reaction Relationships: According to the balanced reaction we need 2 moles of ascorbic acid for every mole of O2.

How much (volume) of a 1 M ascorbic acid solution will completely react with 0.02 moles of oxygen (O2)? Asked: Volume of solution Given: Concentration (1M) and balanced reaction Relationships: According to the balanced reaction we need 2 moles of ascorbic acid for every mole of O2. Solve: That means we need 0.04 moles of ascorbic acid:

How much (volume) of a 1 M ascorbic acid solution will completely react with 0.02 moles of oxygen (O2)? Asked: Volume of solution Given: Concentration (1M) and balanced reaction Relationships: According to the balanced reaction we need 2 moles of ascorbic acid for every mole of O2. Solve: That means we need 0.04 moles of ascorbic acid: Answer: 40 mL of the solution contains 0.04 moles of ascorbic acid, which is enough to react with 0.02 moles of oxygen (O2).

The air you breathe is a mixture!

Air takes up less space under high pressure.

Standard Temperature and Pressure 0oC 1 atm molar volume: the amount of space occupied by a mole of gas at STP. It is equal to 22.4 L. 0oC Standard Temperature and Pressure 1 atm

Partial pressures The total pressure in a mixture of gases is the sum of the partial pressures of each individual gas in the mixture.

+ = + Partial pressures Gas B Gas B Partial pressure of A Gas A Gas A Gas B = Partial pressure of A Partial pressure of B Gas C Total pressure + Gas C Partial pressure of C

If 1 L of helium (75%) and neon (25%) is at STP, what is the partial pressure of helium?

If 1 L of helium (75%) and neon (25%) is at STP, what is the partial pressure of helium? Asked: Partial pressure of helium Given: 75% He and 25% Ne at STP conditions Standard pressure is 101,325 Pa or 1 atm Relationships: The total pressure is the sum of the partial pressures of each gas.

If 1 L of helium (75%) and neon (25%) is at STP, what is the partial pressure of helium? Asked: Partial pressure of helium Given: 75% He and 25% Ne at STP conditions Standard pressure is 101,325 Pa or 1 atm Relationships: The total pressure is the sum of the partial pressures of each gas. Solve:

If 1 L of helium (75%) and neon (25%) is at STP, what is the partial pressure of helium? Asked: Partial pressure of helium Given: 75% He and 25% Ne at STP conditions Standard pressure is 101,325 Pa or 1 atm Relationships: The total pressure is the sum of the partial pressures of each gas. Solve: Answer: The partial pressure of helium is 75,994 Pa or 0.75 atm.

Standard Temperature (0oC) Pressure (1 atm) Concentration of a solution can be expressed in: mass per volume mass percent molarity STP conditions: Standard Temperature (0oC) Pressure (1 atm) Air is a mixture of gases. Based on Dalton’s law of partial pressures: