Unit 1: Solutions - Lecture Flashcards

Comprehensive practice flashcards covering terms, definitions, laws, and chemical principles relating to liquid solutions, concentration units, and colligative properties as discussed in Unit 1.

How is a 'solution' defined in chemistry?

A solution is a homogeneous mixture of two or more than two components where the composition and properties are uniform throughout.

In a solution, what differentiates a 'solvent' from a 'solute'?

The component present in the largest quantity is the solvent, which determines the physical state of the solution. Other components are called solutes.

What is the specific composition of the mixture known as 'brass'?

Brass is a mixture of copper and zinc.

What is the difference in effect between $1\,ppm$ and $1.5\,ppm$ of fluoride ions in water?

$1\,ppm$ of fluoride ions prevents tooth decay, whereas $1.5\,ppm$ causes the teeth to become mottled.

Provide an example of a solid solution where the solute is a liquid and the solvent is a solid.

An amalgam of mercury with sodium.

Define 'Mass percentage (w/w)' and provide its formula.

Mass % of a component is the mass of that component divided by the total mass of the solution multiplied by 100: \text{Mass % of component} = \frac{\text{Mass of component in solution}}{\text{Total mass of solution}} \times 100

What concentration of ethylene glycol solution is used as an antifreeze in car engines, and what is the resulting freezing point?

A $35\%\,(v/v)$ solution is used, which lowers the freezing point of water to $255.4\,K$ ($-17.6^{\circ}C$).

How is 'Parts per million (ppm)' defined for trace solute quantities?

$$\text{Parts per million} = \frac{\text{Number of parts of the component}}{\text{Total number of parts of all components}} \times 10^6$$

Define 'Mole fraction' ($x$) for a component in a binary mixture.

Mole fraction is the ratio of the number of moles of the component to the total number of moles of all components: $x_A = \frac{n_A}{n_A + n_B}$

What is 'Molarity' ($M$), and why is it considered a function of temperature?

Molarity is the number of moles of solute dissolved in one litre of solution ($mol\,L^{-1}$). It depends on temperature because the volume of a solution changes with temperature.

Define 'Molality' ($m$) and state its unit.

Molality is the number of moles of solute per kilogram ($kg$) of the solvent. Its unit is $mol\,kg^{-1}$.

What does the principle 'like dissolves like' signify regarding solubility?

It signifies that polar solutes dissolve in polar solvents and non-polar solutes dissolve in non-polar solvents due to similar intermolecular interactions.

Distinguish between 'dissolution' and 'crystallisation'.

Dissolution is the process of solute dissolving into a solvent, increasing its concentration. Crystallisation occurs when solute particles in solution collide with solid solute particles and separate back out of the solution.

What is a 'saturated solution'?

A solution in which no more solute can be dissolved at the same temperature and pressure, typically being in dynamic equilibrium with undissolved solute.

State Henry's Law.

Henry's Law states that at a constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas present above the surface of the liquid or solution ($p = K_H x$).

How does the Henry’s law constant ($K_H$) relate to gas solubility?

Higher values of $K_H$ at a given pressure indicate lower solubility of the gas in the liquid.

Explain why aquatic species prefer cold water over warm water based on gas solubility.

Solubility of gases like $O_2$ increases with a decrease in temperature ($K_H$ values increase with temperature), meaning cold water contains more dissolved oxygen.

What medical condition is caused by the formation of nitrogen bubbles in the blood of scuba divers, and how is it prevented?

The condition is called 'bends.' It is prevented by filling diving tanks with air diluted with helium ($11.7\%\,He$, $56.2\%\,N_2$, and $32.1\%\,O_2$).

State Raoult’s Law for a solution of volatile liquids.

Raoult's Law states that the partial vapour pressure of each component in the solution is directly proportional to its mole fraction: $p_i = p_i^0 x_i$.

What are the characteristics of an 'ideal solution'?

An ideal solution obeys Raoult’s law over the entire concentration range, with enthalpy of mixing ($\Delta_{mix}H$) and volume of mixing ($\Delta_{mix}V$) both being zero.

Explain what causes 'positive deviation' from Raoult’s law.

Positive deviation occurs when solute-solvent ($A-B$) interactions are weaker than solute-solute ($A-A$) or solvent-solvent ($B-B$) interactions, making it easier for molecules to escape into the vapour phase.

What is an 'azeotrope'?

An azeotrope is a binary mixture that has the same composition in both the liquid and vapour phase and boils at a constant temperature, preventing separation by fractional distillation.

What are the four 'colligative properties' of solutions?

1. Relative lowering of vapour pressure, 2. Elevation of boiling point, 3. Depression of freezing point, 4. Osmotic pressure.

Define 'Boiling Point Elevation Constant' ($K_b$).

Also known as the Ebullioscopic Constant, it is the proportionality constant relating the elevation of boiling point to the molality of the solute: $\Delta T_b = K_b m$.

How is 'osmotic pressure' ($\Pi$) calculated for dilute solutions?

Osmotic pressure is proportional to molarity ($C$) at a given temperature ($T$): $\Pi = C R T$ or $\Pi = (n_2 / V) R T$.

What is the difference between 'isotonic', 'hypertonic', and 'hypotonic' solutions relative to blood cells?

Isotonic solutions have the same osmotic pressure as blood ($0.9\%\,NaCl$); hypertonic solutions have higher salt concentrations causing cells to shrink; hypotonic solutions have lower concentrations causing cells to swell.

What is 'reverse osmosis' and what is its primary industrial application?

Reverse osmosis is the flow of solvent out of a solution through a semipermeable membrane when pressure greater than the osmotic pressure is applied. It is used for the desalination of sea water.

What is the 'van’t Hoff factor' ($i$), and how is it used?

The van’t Hoff factor accounts for the extent of solute dissociation or association. It is defined as: $i = \frac{\text{Normal molar mass}}{\text{Abnormal molar mass}}$ or $i = \frac{\text{Observed colligative property}}{\text{Calculated colligative property}}$

What is 'abnormal molar mass'?

A molar mass that is either lower (due to dissociation) or higher (due to association) than the expected value based on the chemical formula.