Solutions & Mixtures (College Board AP® Chemistry): Flashcards
0Still learning
Know0
Define molarity.
Was this flashcard helpful?
Cards in this collection (46)
Define molarity.
Molarity (M) is the concentration of a solution expressed as the number of moles of solute per litre of solution: M = n / V.
When two KOH solutions are mixed, the molarity of the mixture equals the total moles of KOH divided by the ...........
When two KOH solutions are mixed, the molarity of the mixture equals the total moles of KOH divided by the total volume of the mixture.
True or False?
Adding solvent to a stock solution changes the number of moles of solute present.
False.
Dilution only increases the volume of solvent; the number of moles of solute remains constant. This is the basis of the dilution formula: M1V1 = M2V2.
What is the dilution formula, and what does each symbol represent?
Ms × Vs = Md × Vd, where Ms and Vs are the molarity and volume of the stock solution, and Md and Vd are the molarity and volume of the diluted solution.
For Pb(NO3)2 dissociating in solution, each formula unit produces one Pb2+ ion and .......... NO3- ions.
For Pb(NO3)2 dissociating in solution, each formula unit produces one Pb2+ ion and two NO3- ions.
True or False?
When using the molarity expression M = n / V, volume must always be in litres.
True.
Molarity is defined as moles per litre (mol/L). Converting mL to L before substituting prevents calculation errors.
A student dilutes 5.0 mL of 5.0 M Na2Cr2O7 to 250 mL. What is the molarity of the diluted solution?
Using M1V1 = M2V2: M2 = (5.0 × 5.0) / 250 = 0.10 M.
Define homogeneous mixture.
A homogeneous mixture (also called a solution) is a mixture in which the components are uniformly distributed throughout, giving the mixture the same properties at every point.
True or False?
A mixture of potassium dichromate and iron filings is an example of a homogeneous mixture.
False.
This is a heterogeneous mixture — the two components are physically distinct and have different properties. They can be separated with a magnet.
In a solution, the substance being dissolved is called the .......... and the medium of dissolution is called the solvent.
In a solution, the substance being dissolved is called the solute and the medium of dissolution is called the solvent.
Give one example each of a solid, liquid, and gaseous homogeneous mixture.
Solid: an alloy (e.g. brass). Liquid: sodium chloride dissolved in water. Gaseous: air (a mixture of nitrogen, oxygen and other gases).
True or False?
A colloid is a true solution because it appears homogeneous.
False.
Although a colloid appears homogeneous, it consists of comparatively large particles dispersed throughout another substance — it is not a true solution.
What distinguishes a heterogeneous mixture from a homogeneous mixture?
A heterogeneous mixture consists of physically distinct components with different, visible properties in different regions, whereas a homogeneous mixture has uniform composition and properties throughout.
Define molarity.
Molarity (M) is the concentration of a solution expressed as moles of solute per litre of solution: M = n / V (units: mol/L or M).
A 1.00 M solution contains .......... mol of solute in every 1.0 L of solution.
A 1.00 M solution contains 1.00 mol of solute in every 1.0 L of solution.
True or False?
A dilute solution has a relatively small amount of solute compared to the solvent.
True.
Qualitatively, a dilute solution has a low concentration of solute, while a concentrated solution has a high concentration of solute.
Describe the steps to prepare 250.0 mL of a 1.00 M CuSO4 solution.
Calculate moles needed: n = 1.00 × 0.250 = 0.250 mol. 2. Calculate mass: 0.250 × 159.6 g/mol = 39.9 g. 3. Dissolve 39.9 g CuSO4 in a volumetric flask with some water. 4. Add water to the 250 mL calibration mark.
The dilution formula is Ms × Vs = .......... × V_d, because the number of moles of solute does not change on dilution.
The dilution formula is Ms × Vs = M_d × V_d, because the number of moles of solute does not change on dilution.
True or False?
When using the dilution formula M1V1 = M2V2, the volumes of the two solutions must be in the same units.
True.
The units cancel in the formula, so as long as both volumes use the same unit (both in mL or both in L), the calculation is valid.
Calculate the molarity of a solution made by dissolving 5.00 g of glucose (M_r = 180.2 g/mol) in water to make 100 mL of solution.
n = 5.00 / 180.2 = 0.0277 mol. V = 0.100 L. Molarity = 0.0277 / 0.100 = 0.277 M.
Define solution.
A solution is a homogeneous mixture of two or more substances, consisting of a solute (present in lesser amount) dissolved in a solvent (present in greater amount).
True or False?
In a particulate diagram of a solution, the solute and solvent particles must be evenly distributed throughout the container.
True.
A solution is homogeneous, so solute particles must be uniformly spread. If distinct regions of solute and solvent appear, the diagram represents a heterogeneous mixture, not a solution.
The greater the number of solute particles in a fixed volume, the greater the .......... of the solution.
The greater the number of solute particles in a fixed volume, the greater the concentration of the solution.
In a particulate diagram, how would you distinguish a concentrated solution from a dilute solution of the same solute?
The concentrated solution has more solute particles evenly distributed in the same volume of solvent; the dilute solution has fewer solute particles in the same volume, both with uniform distribution throughout.
True or False?
Any solution in which water is the solvent is called an aqueous solution.
True.
The term "aqueous" (from the Latin for water) specifically refers to solutions where water is the solvent.
Why does a particulate diagram showing separate regions of salt particles and water molecules NOT represent a solution?
A solution is a homogeneous mixture, so solute and solvent particles must be uniformly intermixed. Distinct separate regions mean the mixture is heterogeneous — the solute has not dissolved into the solvent.
Define retention factor (Rf).
The retention factor (Rf) is the ratio of the distance traveled by a component to the distance traveled by the solvent front in chromatography: Rf = distance traveled by component / distance traveled by solvent.
In all forms of chromatography, the .......... is the phase that moves, while the stationary phase remains fixed.
In all forms of chromatography, the mobile phase is the phase that moves, while the stationary phase remains fixed.
True or False?
In paper chromatography, the component that travels the greatest distance has the strongest interaction with the stationary phase.
False.
The component traveling the greatest distance has the strongest interaction with the mobile phase and the weakest interaction with the stationary phase.
In TLC, why must the baseline be placed above the level of the solvent in the container?
If the baseline were submerged, the sample spots would dissolve directly into the solvent rather than being drawn up through the stationary phase by capillary action, destroying the separation.
How does column chromatography differ in mobile phase direction from paper and TLC?
In column chromatography, the mobile phase flows downward through the column under gravity. In paper chromatography and TLC, the mobile phase travels upward through the stationary phase by capillary action.
True or False?
In TLC with a polar stationary phase, a higher Rf value indicates a more polar component.
False.
In normal-phase TLC (polar stationary phase), a more polar component interacts more strongly with the stationary phase and less with the less polar mobile phase. It is retained more and travels a shorter distance, giving a lower Rf. A higher Rf indicates a less polar component.
What stationary phases are commonly used in both TLC and column chromatography?
Silica (SiO2) and alumina (Al2O3). In TLC these are coated onto a thin metal sheet; in column chromatography they are packed inside the column.
Define distillation.
Distillation is a separation technique that exploits differences in boiling points between miscible liquid components; the more volatile component vaporises first, is condensed, and collected separately.
In distillation, the component that vaporises first is the most .......... compound because it has the weakest intermolecular forces.
In distillation, the component that vaporises first is the most volatile compound because it has the weakest intermolecular forces.
True or False?
In the distillation of an ethanol–water mixture, the mixture should be heated to 100 °C to separate the two components.
False.
The mixture should only be heated to 78 °C (ethanol's boiling point). Reaching 100 °C would cause water to evaporate as well, preventing clean separation.
Why does a stronger intermolecular force lead to a higher boiling point in a liquid?
A higher boiling point means more energy is required to overcome the intermolecular forces holding molecules together in the liquid phase. Stronger forces therefore require more thermal energy to vaporise the liquid, raising the boiling point.
When is a fractionating column NOT necessary in distillation?
A fractionating column is not needed when there is a large difference between the boiling points of the components, because they can be cleanly separated without the additional surface area the column provides for equilibration.
True or False?
An electric heater should be used when distilling flammable liquids such as ethanol.
True.
Open flames risk igniting flammable vapours. An electric heater is mandatory to avoid fire hazard when flammable liquids are present.
Define miscible.
Two substances are miscible when they dissolve in each other in all proportions to form a homogeneous solution, because their intermolecular interactions are compatible.
Ion-dipole interactions are the .......... type of intermolecular interaction relevant to solution formation.
Ion-dipole interactions are the strongest type of intermolecular interaction relevant to solution formation.
True or False?
Hexane and water are miscible because both molecules experience London dispersion forces.
False.
Water molecules interact via hydrogen bonding (stronger), while hexane–water interactions are London dispersion forces (weaker). Because the solvent-solute interaction is weaker than the solvent-solvent interaction, hexane and water are immiscible.
Under what condition does a solution form when the solvent-solvent and solute-solute interactions are different?
A solution forms when the solvent-solute interaction is stronger than or equal to the solvent-solvent interaction. If the solvent-solute interaction is weaker than the solvent-solvent interaction, a solution may not form.
Explain why salt (NaCl) dissolves readily in water using intermolecular interaction terms.
Salt produces Na+ and Cl- ions that form ion-dipole interactions with polar water molecules. These ion-dipole interactions are stronger than the hydrogen bonding between water molecules, so the solvent-solute interaction exceeds the solvent-solvent interaction and a solution forms.
True or False?
Ethanol and water are miscible because both exhibit hydrogen bonding.
True.
Both ethanol and water form hydrogen bonds. Because the solvent-solvent and solute-solute interactions are the same type, the two liquids are miscible in one another.
Rank the following from weakest to strongest intermolecular interaction: London dispersion forces, hydrogen bonding, dipole-dipole, ion-dipole.
Weakest to strongest: London dispersion forces < dipole-dipole < hydrogen bonding < ion-dipole.
Sign up to unlock flashcards
or