Chapter 13: Properties of Solutions

Flashcards covering Chapter 13: Properties of Solutions, including definitions, types, factors affecting solubility, concentration units, colligative properties, and related biological applications.

What are solutions and what do they consist of?

Solutions are homogeneous mixtures of two or more substances, consisting of a solvent and one or more solutes.

What are the characteristics of solutes in a solution?

Solutes spread evenly throughout the solution, cannot be separated by filtration, can be separated by evaporation, and are not visible but can give color to the solution.

Provide an example of a gas in a gas solution.

Air (Oxygen in Nitrogen)

Provide an example of a liquid in a liquid solution.

Vinegar (Acetic acid in Water)

Provide an example of a solid in a liquid solution.

Seawater (Sodium chloride in Water)

Provide an example of a solid in a solid solution.

Brass (Zinc in Copper)

What must be true about the intermolecular forces between solute and solvent particles for a solution to form?

The intermolecular forces between solute and solvent particles must be strong enough to compete with those between solute particles and those between solvent particles.

How does a solution form at a molecular level?

As a solution forms, the solvent pulls solute particles apart and surrounds, or solvates, them.

What are two key characteristics of water as a solvent?

Water is the most common solvent and is a polar molecule.

How are Na+ and Cl- ions affected when a NaCl crystal dissolves in water?

Na+ and Cl- ions on the surface of a NaCl crystal are attracted to polar water molecules and are hydrated in solution with many H2O molecules surrounding each ion.

Write the equation for NaCl(s) dissolving in water.

H2O NaCl(s) → Na+(aq) + Cl-(aq)

Why is an ionic salt soluble in water?

An ionic salt is soluble in water because the ion-dipole interactions are strong enough to overcome the lattice energy of the salt crystal.

What is the general principle regarding solubility that chemists use?

Chemists use the axiom 'like dissolves like': Polar substances tend to dissolve in polar solvents, and nonpolar substances tend to dissolve in nonpolar solvents.

What factor significantly increases the likelihood of one substance being soluble in another?

The more similar the intermolecular attractions, the more likely one substance is to be soluble in another.

Why is glucose highly soluble in water, while cyclohexane is not?

Glucose has hydrogen bonding, making it very soluble in water, while cyclohexane only has dispersion forces, making it not soluble.

What is an example of a vitamin soluble in nonpolar compounds? What about in water?

Vitamin A is soluble in nonpolar compounds (like fats), and Vitamin C is soluble in water.

Will Na2SO4 dissolve in water? Why?

Yes, Na2SO4 will dissolve in water because it is ionic.

Will gasoline dissolve in water? Why?

No, gasoline will not dissolve in water because it is nonpolar.

Will HCl dissolve in water? Why?

Yes, HCl will dissolve in water because it is polar.

What are the three processes that affect the energetics of solution formation?

Separation of solute particles, separation of solvent particles, and new interactions between solute and solvent.

Besides enthalpy, what other factor plays a role in lowering the energy of a system during solution formation?

Increasing the disorder or randomness, known as entropy, tends to lower the energy of the system.

How can one distinguish between a substance dissolving and a substance reacting with the solvent?

Dissolution is a physical change where the original solute can be recovered by evaporating the solvent. If you cannot, the substance reacted.

Define solubility and how it is typically expressed.

Solubility is the maximum amount of solute that dissolves in a specific amount of solvent, expressed as grams of solute in 100 grams of water.

What is an unsaturated solution?

Unsaturated solutions contain less than the maximum amount of solute and can dissolve more solute.

What is a saturated solution?

Saturated solutions contain the maximum amount of solute that can dissolve and have undissolved solute at the bottom of the container.

What is a supersaturated solution, and how can crystallization be stimulated in it?

A supersaturated solution holds more solute than is normally possible at that temperature. Crystallization can usually be stimulated by adding a 'seed crystal' or scratching the side of the flask.

At 40°C, the solubility of KBr is 80 g/100 g H2O. Is a solution with 60 g KBr added to 100 g of water at 40°C saturated or unsaturated?

Unsaturated, because 60 g is less than the maximum solubility of 80 g.

How does the solubility of gases in water generally change with increasing mass?

In general, the solubility of gases in water increases with increasing mass, as larger molecules have stronger dispersion forces.

How does pressure affect the solubility of liquids and solids in a solvent, compared to gases?

The solubility of liquids and solids does not change appreciably with pressure, but the solubility of a gas in a liquid is directly proportional to its pressure.

State Henry's Law.

Henry's Law states that the solubility of a gas in a liquid is directly related to the pressure of that gas above the liquid.

Write the equation for Henry's Law and define its variables.

Sg = kPg, where Sg is the solubility of the gas, k is the Henry's law constant for that gas in that solvent, and Pg is the partial pressure of the gas above the liquid.

How does temperature generally affect the solubility of solid solutes in liquid solvents?

Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature.

How does temperature affect the solubility of gases in water?

The solubility of gases in water decreases with increasing temperature.

Why are carbonated soft drinks more 'bubbly' if stored in the refrigerator?

Carbonated soft drinks are more bubbly if stored in the refrigerator because gases (like CO2) are less soluble in warmer water.

How is the concentration of a solution defined?

The concentration of a solution is the amount of solute dissolved in a specific amount of solution (amount of solute / amount of solution).

Define mass percent and provide its formula.

Mass percent (%m/m) is the percent by mass of solute in a solution, calculated as (g of solute / (g of solute + g of solvent)) × 100 or (g of solute / 100 g of solution) × 100.

Define volume percent and provide its formula.

Volume percent (%v/v) is the percent volume (mL) of solute (liquid) to volume (mL) of solution, calculated as (mL of solute / mL of solution) × 100 or (mL of solute / 100 mL of solution) × 100.

Define mass/volume percent and provide its formula.

Mass/volume percent (%m/v) is the percent mass (g) of solute to volume (mL) of solution, calculated as (g of solute / mL of solution) × 100 or (g of solute / 100 mL of solution) × 100.

How many grams of NaCl are needed to prepare 225 g of a 10.0% (m/m) NaCl solution?

22.5 g NaCl

How many mL of a 4.20% (m/v) KCl solution will contain 3.15 g KCl?

75.0 mL KCl solution

Provide the formula for Parts per Million (ppm) and Parts per Billion (ppb).

ppm = (mass of A in solution / total mass of solution) × 10^6; ppb = (mass of A in solution / total mass of solution) × 10^9

Provide the formula for Mole Fraction (XA).

XA = amount solute (moles) / total moles in solution

Define molarity and provide its formula.

Molarity (M) is a concentration term for solutions that gives the moles of solute in 1 L solution, calculated as moles of solute / liter of solution.

How is a 1.00 M NaCl solution prepared?

A 1.00 M NaCl solution is prepared by weighing out 58.5 g NaCl (1.00 mole), dissolving it in water, and then adding water to make 1.00 liter of solution.

How many grams of KCl are needed to prepare 125 mL of a 0.720 M KCl solution? (Assume molar mass of KCl is 74.6 g/mol)

6.71 g KCl

What happens to a solution during dilution?

In a dilution, water is added, the volume increases, and the concentration decreases.

What are the equations used to relate concentrations and volumes for initial and diluted solutions (for both percent concentration and molarity)?

For percent concentration: C1V1 = C2V2; For molarity: M1V1 = M2V2.

What volume of a 2.00% (m/v) HCl solution can be prepared by diluting 25.0 mL of 14.0% (m/v) HCl solution?

175 mL

What is the molarity (M) of a solution prepared by diluting 0.180 L of 0.600 M HNO3 to 0.540 L?

0.200 M

How is molarity used in chemical reactions to determine moles of a reactant or product?

In a chemical reaction, the volume and molarity of a solution are used to determine the moles of a reactant or product using the formula: molarity (mole/L) × volume (L) = moles.

How many mL of 3.00 M HCl are needed to completely react with 4.85 g CaCO3 given the reaction 2 HCl(aq) + CaCO3(s) → CaCl2(aq) + CO2(g) + H2O(l)? (Assume molar mass of CaCO3 is 100.1 g/mol)

32.3 mL HCl

Why can molarity change with temperature?

Molarity can change with temperature because volume is temperature dependent.

Define molality and explain why it is not temperature dependent.

Molality (m) is defined as moles of solute / kg of solvent. It is not temperature dependent because both moles and mass do not change with temperature.

What are colligative properties, and what do they depend on? List some examples.

Colligative properties depend only on the number of solute particles present, not on their identity. Examples include vapor pressure lowering, boiling point elevation, melting point depression, and osmotic pressure.

How do nonvolatile solutes affect the vapor pressure of a solvent?

Nonvolatile solutes make it harder for solvent to escape to the vapor phase, thus lowering the vapor pressure of the solution compared to the pure solvent.

State Raoult's Law and define its variables.

PA = XAP°A, where XA is the mole fraction of compound A, and P°A is the normal vapor pressure of A at that temperature. (PA is the partial pressure of A above the solution.)

How do nonvolatile solute-solvent interactions affect the boiling and freezing points of solutions compared to pure solvents?

Nonvolatile solute-solvent interactions cause solutions to have higher boiling points and lower freezing points than the pure solvent.

Provide the formula for boiling point elevation and define Kb.

ΔTb = Kb × m, where Kb is the molal boiling point elevation constant, a property of the solvent.

Provide the formula for freezing point depression and define Kf.

ΔTf = Kf × m, where Kf is the molal freezing point depression constant of the solvent.

In boiling point elevation and freezing point depression, what does the change in temperature (ΔT) depend on?

ΔT does not depend on what the solute is, but only on how many particles are dissolved.

How should solutions of electrolytes affect colligative properties compared to nonelectrolytes?

Since colligative properties depend on the number of particles dissolved, solutions of electrolytes (which dissociate) should show greater changes than those of nonelectrolytes.

Which aqueous solution will have the lowest freezing point: 0.25 m C2H5OH, 0.15 m CaCl2, 0.20 m NaCl, 0.15 m NH4NO3, or 0.15 m Na3PO4?

0.15 m Na3PO4 (it produces the most particles per mole, 4 ions, so 0.15 * 4 = 0.6 m effective concentration, which is highest)

Why does a 1 M NaCl solution not show exactly twice the change in freezing point as a 1 M methanol solution?

Some Na+ and Cl- ions reassociate for a short time, so the true concentration of particles is somewhat less than two times the concentration of NaCl.

What is the reason that one mole of NaCl in water does not truly give rise to two moles of ions?

Some Na+ and Cl- ions reassociate for a short time.

How does reassociation affect the van't Hoff factor and the true number of particles present?

Reassociation is more likely at higher concentrations, making the number of particles present concentration dependent, and therefore affecting the van't Hoff factor value.

How is the freezing point depression equation modified to account for electrolytes?

The equation is multiplied by the van't Hoff factor (i): ΔTf = Kf × m × i.

What are semipermeable membranes, and how do they function in biological systems regarding osmosis?

Semipermeable membranes allow some smaller particles (like solvent) to pass through, but block larger particles (like solutes). In biological systems, most allow water to pass but solutes do not.

Describe the direction of water flow in osmosis.

Water (solvent) flows from the lower solute concentration into the higher solute concentration.

If a semipermeable membrane separates a 4% starch solution from a 10% starch solution, describe what happens due to osmosis.

The 10% starch solution is diluted by water flowing out of the 4% solution. The 4% solution loses water and its volume decreases, while the 10% solution volume increases, until concentrations equalize.

In osmosis, from which area does the net movement of solvent occur?

There is net movement of solvent from the area of higher solvent concentration (lower solute concentration) to the area of lower solvent concentration (higher solute concentration).

Define osmotic pressure.

Osmotic pressure is the pressure produced by the solute particles dissolved in a solution, equal to the pressure that would prevent the flow of additional water into the more concentrated solution.

What is the formula for osmotic pressure, and what are isotonic solutions?

Osmotic pressure, π = (n/V)RT = MRT, where M is the molarity of the solution. Isotonic solutions have the same osmotic pressure on both sides of a membrane (i.e., concentrations are the same).

Describe isotonic solutions and give an example of their medical use.

Isotonic solutions exert the same osmotic pressure as red blood cells, also known as 'physiological solutions'. A 0.90% NaCl solution is used medically because its solute concentration equals the osmotic pressure of red blood cells.

What is a hypotonic solution, and what effect does it have on red blood cells?

A hypotonic solution has a lower osmotic pressure than red blood cells. It causes water to flow into red blood cells, leading to hemolysis (RBCs swell and may burst).

What is a hypertonic solution, and what effect does it have on red blood cells?

A hypertonic solution has a higher osmotic pressure than red blood cells. It causes water to flow out of red blood cells, leading to crenation (RBCs shrink in size).

Define dialysis and provide an example of its application.

In dialysis, solvent and small solute particles pass through an artificial membrane, while large particles are retained. An example is hemodialysis, which removes waste particles like urea from blood using an artificial kidney.

List the key characteristics of solutions.

Solutions contain small particles (ions or molecules), are transparent, do not separate, cannot be filtered, and do not scatter light.

What are colloids?

Colloids are suspensions of particles larger than individual ions or molecules, but too small to be settled out by gravity.

What are suspensions? List some characteristics and examples.

Suspensions have very large particles, settle out, can be filtered, and must be stirred to stay suspended. Examples include blood platelets, muddy water, and Calamine lotion.

Describe the dual nature of some molecules found in colloidal biological systems.

Some molecules have a polar, hydrophilic (water-loving) end and a nonpolar, hydrophobic (water-hating) end.