Free Master of Chemistry: Physical Chemistry Questions and Answers — Questions and Answers

Question 1: It is referred to as the solute concentration per unit volume.

ppm
molality
concentration (Correct answer)
mass

Correct answer: concentration

Concentration is a general quantitative term used to express the amount of solute present in a given amount of solvent or total solution. It quantifies how much of a substance is dissolved or dispersed in another substance, typically expressed as mass per unit volume or moles per unit volume. While ppm and molality are specific units of concentration, 'concentration' is the overarching concept.

Question 2: if 2g of NaCl is dissolved in 20g of water, then the solution's percentage is

12%
9% (Correct answer)
7%
5%

Correct answer: 9%

To calculate the percentage concentration (mass/mass), we use the formula: (mass of solute / total mass of solution) * 100%. Here, the mass of solute (NaCl) is 2g, and the mass of solvent (water) is 20g. The total mass of the solution is 2g + 20g = 22g. Therefore, the percentage is (2g / 22g) * 100% ≈ 9.09%, which rounds to 9%.

Question 3: Choose the inaccurate composition percentage expression.

m/v %
m/m%
m/d% (Correct answer)
v/v %

Correct answer: m/d%

Common composition percentage expressions include mass/mass (m/m%), mass/volume (m/v%), and volume/volume (v/v%). These units clearly define the components being measured. The expression 'm/d%' is not a standard or recognized unit for expressing composition percentage in chemistry, making it the inaccurate option.

Question 4: Pa is the SI unit for pressure. equivalent to

1N/M
1Nm
1N/m² (Correct answer)
1N/m

Correct answer: 1N/m²

Pressure is fundamentally defined as force applied per unit area. In the International System of Units (SI), the unit for force is the Newton (N), and the unit for area is the square meter (m²). Therefore, one Pascal (Pa), the SI unit for pressure, is equivalent to one Newton per square meter (1 N/m²).

Question 5: Which one compresses more easily?

solution
solid
liquid
gas (Correct answer)

Correct answer: gas

Gases are the most compressible state of matter because their particles are widely spaced and experience very weak intermolecular forces. This allows them to be forced into a much smaller volume under pressure. Solids and liquids have particles that are already closely packed, making them significantly less compressible.

Question 6: Which of the following is not a relationship?

1m3=10cm³
1L=1dm³
1ml=1cm³ (Correct answer)
100L=100dm³

Correct answer: 1ml=1cm³

The relationship 1m³ = 10cm³ is incorrect. Since 1 meter (m) equals 100 centimeters (cm), 1 cubic meter (1 m³) is equivalent to (100 cm)³, which is 1,000,000 cm³. The other options represent correct standard unit conversions in chemistry: 1L = 1dm³, 1mL = 1cm³, and thus 100L = 100dm³.

Question 7: Energy needed to stop a reaction is referred to as

specific heat
activation energy (Correct answer)
minimum potential energy
maximum potential energy

Correct answer: activation energy

Activation energy is the minimum amount of energy that reactant molecules must possess to overcome the energy barrier and initiate a chemical reaction. It represents the energy required to reach the transition state, allowing reactants to transform into products. Without sufficient activation energy, a reaction will not proceed or will proceed very slowly.

Question 8: The relationship between a substance's concentration and the quantity of energy it absorbs is provided by

Snell’s law
Avogadro’s law
Beer’s law (Correct answer)
Lambert law

Correct answer: Beer’s law

Beer's Law, often combined with Lambert's Law as the Beer-Lambert Law, describes the linear relationship between the absorbance of light by a solution and its concentration. It states that absorbance is directly proportional to both the concentration of the absorbing species and the path length of the light through the solution. This principle is fundamental to quantitative analysis using spectrophotometry.

Question 9: Surface-adsorbed chemicals are known as surfactants, and surface tension is

varied
increased
remain constant
decreased (Correct answer)

Correct answer: decreased

Surfactants are compounds that, when added to a liquid, reduce its surface tension. They achieve this by adsorbing at the liquid-air or liquid-liquid interface, disrupting the cohesive forces between liquid molecules at the surface. This property makes them useful in applications like detergents, emulsifiers, and wetting agents.

Question 10: The rate at which phenolphthalein fades in basic solution is

0th order
1st order (Correct answer)
2nd order
3rd order

Correct answer: 1st order

The fading of phenolphthalein in a basic solution is a classic example of a chemical reaction whose rate depends on the concentration of the reactants. Experimental studies typically show that this reaction follows first-order kinetics with respect to phenolphthalein, meaning its rate of disappearance is directly proportional to its concentration.

Question 11: Solvent and solute concentrations can both be stated as

moles
volume
mass
all of these (Correct answer)

Correct answer: all of these

Concentrations of both solvents and solutes can be expressed using various units depending on the context. These include mass-based units (e.g., grams, kilograms, mass percentage), volume-based units (e.g., milliliters, liters, volume percentage), and mole-based units (e.g., moles, molarity). Therefore, all these options represent valid ways to state concentrations.

Question 12: To make 25 ml of 0.06 M solution, how much 0.1 M stock solution is needed?

25ml
20ml
10 ml
15ml (Correct answer)

Correct answer: 15ml

To solve this dilution problem, we use the formula M1V1 = M2V2, where M1 is the initial molarity, V1 is the initial volume, M2 is the final molarity, and V2 is the final volume. Given M1 = 0.1 M, M2 = 0.06 M, and V2 = 25 mL, we calculate V1 = (0.06 M * 25 mL) / 0.1 M = 15 mL. Thus, 15 mL of the 0.1 M stock solution is needed.

Question 13: When an unsaturated solution is overconcentrated, it transforms into

colloidal solution
unsaturated solution
supersaturated solution
saturated solution (Correct answer)

Correct answer: saturated solution

An unsaturated solution contains less solute than the maximum amount that can be dissolved at a given temperature. When more solute is added to an unsaturated solution until the maximum solubility limit is reached, the solution becomes saturated. At this point, no more solute can dissolve, and any additional solute will typically remain undissolved or precipitate out.

Question 14: Choose the answer that has nothing to do with homogeneous mixture.

It has homogeneous composition
It has single phase
It is composed of two or more different molecular or ionic substances
Its example is solution of sand in water (Correct answer)

Correct answer: Its example is solution of sand in water

A homogeneous mixture has a uniform composition and properties throughout, appearing as a single phase (e.g., sugar dissolved in water). A solution of sand in water, however, is a heterogeneous mixture because the sand particles do not dissolve and remain visibly distinct, forming separate phases from the water.

Question 15: Using a sample that is white, you can see that there is absorption.

0% (Correct answer)
1%
10%
100%

Correct answer: 0%

A perfectly white sample reflects all wavelengths of visible light equally and completely. This means that it absorbs none of the incident visible light. Therefore, for a white sample, the absorption percentage of visible light is ideally 0%.

Question 16: Which word applies to a mole of carbon and a mole of helium?

density
molecules
atom (Correct answer)
Mass

Correct answer: atom

A mole of any element contains Avogadro's number (approximately 6.022 x 10^23) of its constituent particles. For elemental substances like carbon and helium, these constituent particles are individual atoms. Therefore, a mole of carbon contains Avogadro's number of carbon atoms, and a mole of helium contains Avogadro's number of helium atoms.

Free Master of Chemistry: Physical Chemistry Questions and Answers

It is referred to as the solute concentration per unit volume.