Solutions and Mixtures Overview
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What is the molality of a solution prepared by dissolving 18.0 g of glucose (C6H12O6) in 250.0 g of water?

  • 2.50 m
  • 0.391 m (correct)
  • 1.25 m
  • 0.782 m

    • Which of the following statements is TRUE regarding the entropy of a system?

  • Entropy is a measure of the disorder or randomness of a system. (correct)
  • Entropy is always a constant value for a given system.
  • The entropy of a solid is greater than the entropy of a liquid.
  • The entropy of a gas is less than the entropy of a liquid.

    • Why is the mixing of gases a spontaneous process?

  • Gases are more likely to react with each other than liquids or solids.
  • Gases are always at a higher temperature than liquids or solids.
  • Gases have a higher entropy than liquids or solids. (correct)
  • Gases have a higher density than liquids or solids.

    • What is the mass of KBr in 35.8 mL of a potassium bromide solution that is 7.55% KBr by mass and has a density of 1.03 g/mL?

    <p>2.76 g (B)</p> Signup and view all the answers

    What is the concentration of Zn2+ in parts per million (ppm) if a 2.5 g sample of groundwater contains 5.4 μg of Zn2+?

    <p>2.16 ppm (A)</p> Signup and view all the answers

    What is the key distinction between a saturated solution and an unsaturated solution?

    <p>A saturated solution is at equilibrium, with undissolved solute present. (C)</p> Signup and view all the answers

    A solution is prepared by dissolving 10.0 g of NaCl in 500.0 g of water. What is the molality of the solution?

    <p>0.34 m (B)</p> Signup and view all the answers

    Which of the following factors does NOT influence the ability of substances to form solutions?

    <p>The color of the substances. (B)</p> Signup and view all the answers

    What is the best definition of solubility?

    <p>The maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature. (D)</p> Signup and view all the answers

    What is the molarity of a 6.56% by mass glucose (C6H12O6) solution if the density of the solution is 1.03 g/mL?

    <p>0.375 M (C)</p> Signup and view all the answers

    Which of the following DOES NOT describe a characteristic of a supersaturated solution?

    <p>It is an equilibrium state between dissolution and crystallization. (D)</p> Signup and view all the answers

    What is the primary difference between a solution and a mixture?

    <p>Solutions are homogeneous mixtures, while mixtures can be heterogeneous. (B)</p> Signup and view all the answers

    Which of the following is NOT a typical example of a solution?

    <p>Sand and water. (D)</p> Signup and view all the answers

    In the context of solutions, what does the term 'solute' refer to?

    <p>The substance that is being dissolved in the solution. (C)</p> Signup and view all the answers

    If a solution contains 20g of NaCl in 100mL of water at 0ºC, and the solubility of NaCl at 0ºC is 35.7g per 100mL, which of the following statements is true?

    <p>The solution is unsaturated. (D)</p> Signup and view all the answers

    What is the most likely reason that a solution is supersaturated?

    <p>The solute was dissolved at a higher temperature and then cooled. (A)</p> Signup and view all the answers

    Which of the following statements is true about the solubility of gases in liquids?

    <p>The solubility of gases in liquids decreases with increasing temperature. (C)</p> Signup and view all the answers

    Which of the following is NOT a colligative property?

    <p>Viscosity (D)</p> Signup and view all the answers

    Why does adding salt to boiling water briefly stop the water from boiling?

    <p>The salt lowers the vapor pressure of the water, making it harder for the water to boil. (D)</p> Signup and view all the answers

    What is the relationship between the mole fraction of a solvent and the vapor pressure of the solution?

    <p>The vapor pressure of the solution is directly proportional to the mole fraction of the solvent. (C)</p> Signup and view all the answers

    What is the vapor pressure of a solution containing 0.8 moles of water and 0.2 moles of glucose at 20°C, if the vapor pressure of pure water at 20°C is 17.5 torr?

    <p>14 torr (D)</p> Signup and view all the answers

    Which of the following factors affects the solubility of a solid solute in a liquid solvent?

    <p>The temperature of the system (A)</p> Signup and view all the answers

    Which of the following is a colligative property that can be used to determine the molecular weight of a solute?

    <p>All of the above (D)</p> Signup and view all the answers

    What is the Henry's Law constant for oxygen (O2) in water at 25°C, if the solubility of O2 in water at this temperature and a partial pressure of 1 atm is 1.3 × 10⁻³ M?

    <p>1.3 × 10⁻³ M/atm (C)</p> Signup and view all the answers

    Which of the following compounds will be most soluble in ethanol (CH3CH2OH)?

    <p>Ethylene glycol (HOCH2CH2OH) (D)</p> Signup and view all the answers

    The principal reason for the extremely low solubility of NaCl in benzene (C6H6) is the ________.

    <p>Weak solvation of Na+ and Cl- by C6H6 (D)</p> Signup and view all the answers

    Which one of the following substances is more likely to dissolve in CCl4?

    <p>CBr4 (C)</p> Signup and view all the answers

    What does Henry’s Law express in relation to gases?

    <p>Gas solubility is directly proportional to its partial pressure (D)</p> Signup and view all the answers

    If the Henry’s Law constant for a gas in a solvent is 3.4 x 10^-2 M/atm, what is the required pressure to achieve a concentration of 0.12 M?

    <p>3.53 atm (C)</p> Signup and view all the answers

    What is the effect of increasing pressure on the solubility of a gas in a liquid?

    <p>Increases solubility (B)</p> Signup and view all the answers

    Why are polar solvents ineffective in dissolving nonpolar solutes?

    <p>Their intermolecular forces differ significantly (C)</p> Signup and view all the answers

    Under what circumstances is a solute most likely to dissolve in a solvent?

    <p>When the solute and solvent have similar intermolecular forces (D)</p> Signup and view all the answers

    What is the effect of adding a nonvolatile solute to a solvent?

    <p>It lowers the vapor pressure of the solvent. (D)</p> Signup and view all the answers

    Which of the following equations represents the relationship between vapor-pressure lowering and solute concentration?

    <p>ΔP = Xsolute P⁰solvent (C)</p> Signup and view all the answers

    How is the boiling point of a solution affected by the presence of solute particles?

    <p>It increases due to reduced vapor pressure. (C)</p> Signup and view all the answers

    What happens to the freezing point of a solvent when a nonvolatile solute is added?

    <p>It decreases, making freezing harder. (C)</p> Signup and view all the answers

    What does the boiling-point elevation constant (Kb) depend on?

    <p>The nature of the solvent used. (B)</p> Signup and view all the answers

    Which condition signifies that a liquid is boiling?

    <p>The vapor pressure equals the air pressure. (B)</p> Signup and view all the answers

    What is the primary reason that salting ice can freeze ice cream?

    <p>It lowers the freezing point of water. (B)</p> Signup and view all the answers

    The change in boiling point for a solution is directly proportional to which factor?

    <p>The concentration of solute particles in the solution. (A)</p> Signup and view all the answers

    What is the change in freezing point of a solution for which the freezing point of the solvent is 0°C and the freezing point of the solution is -2.5°C?

    <p>2.5°C (C)</p> Signup and view all the answers

    Which of the following factors does the change in freezing point of a solution NOT depend on?

    <p>The identity of the solute (C)</p> Signup and view all the answers

    What would be the freezing point of a solution that contains 0.5 moles of sodium chloride (NaCl) dissolved in 1 kg of water?

    <p>-3.72°C (A)</p> Signup and view all the answers

    A solution containing 10 g of glucose (C6H12O6) in 100 g of water has a freezing point of -0.558°C. What is the van't Hoff factor (i) for this solution?

    <p>1 (B)</p> Signup and view all the answers

    Which of the following solutions would have the lowest freezing point?

    <p>0.1 m aqueous FeCl3 (B)</p> Signup and view all the answers

    A solution is prepared by dissolving 5.85 g of NaCl in 100 g of water. What is the freezing point of this solution assuming ideal behavior?

    <p>-3.72°C (D)</p> Signup and view all the answers

    A solution containing 10 g of sucrose (C12H22O11) in 100 g of water has a freezing point of -0.284°C. What is the molal freezing-point depression constant (Kf) for water?

    <p>1.86°C/m (A)</p> Signup and view all the answers

    What is the osmotic pressure of a solution containing 0.1 mol of glucose (C6H12O6) dissolved in 1 L of water at 25°C?

    <p>2.46 atm (D)</p> Signup and view all the answers

    Study Notes

    Solutions: Mixing It Up

    • Matter encountered in daily life are mixtures
    • Mixtures can be solid (e.g., a porch chair), liquid (e.g., coffee) or gaseous (e.g., air)
    • Air is a mixture of N₂, O₂, CO₂, and other elements
    • Coffee is a mixture containing cellulose, sugars, and water

    Solutions: Homogeneous Mixtures

    • Solutions are homogeneous mixtures of two or more pure substances
    • Each substance in a solution is a component
    • The solvent is the component present in the greatest amount
    • All other components are solutes, uniformly dispersed throughout the solvent
    • Aqueous solutions have water as the solvent, with either gas, liquid or solid as the solute

    Saturated Solutions and Solubility

    • A saturated solution holds the maximum amount of solute possible at a given temperature
    • Additional solute will not dissolve in a saturated solution
    • Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature
    • Example: the solubility of NaCl in H₂O at 0°C is 35.7 g per 100 mL of water

    Types of Solutions

    Unsaturated

    • An unsaturated solution contains less solute than the solvent can dissolve at that temperature
    • A solution containing 10g of NaCl per 100mL of water at 0°C is unsaturated, meaning more solute can be dissolved.

    Supersaturated

    • In a supersaturated solution, the solvent holds more solute than is normally possible at that temperature
    • These solutions are unstable and crystallization can be stimulated by adding a "seed crystal" or scratching the sides of the container
    • Rock candy grows when a string is suspended in a supersaturated sugar solution

    Ways of Expressing Solution Concentrations

    Mass Percentage

    • Mass % of A = (mass of A in solution/total mass of solution) * 100
    • Example: vinegar is a 5% by mass solution of acetic acid in water.

    Parts per Million (ppm) and Parts per Billion (ppb)

    • ppm = (Mass of A in solution/Total mass of solution) * 10⁶
    • ppb = (Mass of A in solution /Total mass of solution) * 10⁹

    Mole Fraction (X)

    • Xₐ = (moles of A/total moles of all components)
    • Mole fractions have no units
    • The sum of the mole fractions of all components equals 1
    • Example: 1 mole of HCl and 8 moles of H₂O in a solution has a mole fraction of XHCl = 0.111 and XH₂O = 0.889.

    Molarity (M)

    • M = (moles of solute/liters of solution)
    • Molarity is temperature-dependent

    Molality (m)

    • m = (moles of solute/kilograms of solvent)
    • Molality is not temperature-dependent

    The Solution Process

    • The ability of substances to form solutions depends on two factors
    1. The natural tendency of substances to mix and spread into larger volumes
    2. The types of intermolecular interactions involved in solution processes

    Entropy of Solutions

    • Entropy, is related to the number of ways a system can disperse its energy, related to the freedom of motion of the particles.
    • In solids, particles are fixed, little freedom of motion
    • In liquids, particles move around each other, greater freedom of motion
    • In gases, particles have little restriction, much more freedom of motion
    • The more freedom of motion, the more ways they can distribute their energy; thus Sgas > Sliquid > Ssolid.
    • Solution formation involves a change in entropy; usually a solution has higher entropy than the pure solute and pure solvent.
    • There are more interactions when solute and solvent mix than when they are pure.

    Intermolecular Forces on Solution Formation

    • Gases spontaneously mix, but liquid and solid solvents and solutes involve intermolecular forces that determine whether a solution forms.
    • Miscibility implies that liquids mix in all proportions, while immiscibility means that they do not mix.
    • Factors affecting solubility of solutes in solvents are:
      1. Solute-solute interactions
      2. Solvent-solvent interactions
      3. Solvent-solute interactions (solvation)

    Energetics of Solution Formation

    • Solution formation involves changes in enthalpy (heat)
    • Solutions can be exothermic (release heat) or endothermic (absorb heat)
    • Three factors affecting enthalpy changes are: separation of solute, separation of solvent, and new interactions between solute and solvent

    Hot/Cold Packs

    • Hot packs utilize exothermic solution processes (releasing heat)
    • Cold packs utilize endothermic solution processes (absorbing heat)

    Colligative Properties

    • Physical properties of solutions that depend on the number of solute particles, not their identity
    • Examples: vapor-pressure lowering, boiling-point elevation, freezing-point depression, osmotic pressure

    Vapor-Pressure Lowering

    • When a non-volatile solute is added to a solvent, the vapor pressure of the solvent decreases
    • Fewer solvent molecules have enough energy to escape into the gaseous phase because of solute-solvent interactions

    Raoult's Law

    • The vapor pressure of a solution is proportional to the mole fraction of the solvent and the vapor pressure of the pure solvent
    • Psolution = XA * PA

    Boiling-Point Elevation

    • The presence of a non-volatile solute in a solvent raises the boiling point of the solution above that of the pure solvent. This occurs because higher solute concentrations in the solution make it more difficult for the solvent to escape into the gaseous phase

    Freezing-Point Depression

    • The presence of a non-volatile solute in a solvent lowers the freezing point of the solution below that of the pure solvent, as solute particles interfere with solvent molecules' ability to form a crystal structure
    • The change in freezing point is calculated using the equation ΔTf = - i * Kf * m

    Osmosis

    • Osmosis is the movement of solvent molecules across a semipermeable membrane from an area of higher solvent concentration (lower solute concentration) to an area of lower solvent concentration (higher solute concentration to equalize the solute concentrations on both sides of the membrane)
    • Osmotic pressure is the pressure required to stop osmosis.

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    Description

    Explore the concepts of mixtures and solutions in this quiz, including their definitions and examples from daily life. Understand the differences between homogeneous and heterogeneous mixtures, and learn about saturated solutions and solubility. Test your knowledge with practical examples and definitions.

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