# FREE Master of Chemistry: Physical Chemistry Questions and Answers

#### Which word applies to a mole of carbon and a mole of helium?

The term that is the same for 1 mole of carbon and 1 mole of helium is atom. In chemistry, one mole of any substance contains the same number of entities, which is known as Avogadro's number (6.022 x 10^23 entities/mole). So, one mole of carbon and one mole of helium both contain the same number of atoms, which is equal to Avogadro's number.

#### Which of the following is not a relationship?

In the International System of Units (SI), 1 milliliter (ml) is defined as equal to 1 cubic centimeter (cm³). This relationship is a direct consequence of the definition of the base unit of length, the meter (m), and the fact that 1 liter (L) is defined as 1 decimeter cubed (dm³) or 1,000 cm³. So, 1 ml is indeed equal to 1 cm³, and they are related to one another in terms of volume measurement.

#### Solvent and solute concentrations can both be stated as

Concentration can be expressed in terms of mass, volume, or moles, and each unit has its specific purpose and relevance in different situations.

#### Surface-adsorbed chemicals are known as surfactants, and surface tension is

Surfactants are substances that get adsorbed at the surface of a liquid and they generally decrease the surface tension of the liquid. Surface tension is a property of the liquid that describes the force per unit length acting on the surface. In the absence of surfactants, the surface tension tends to minimize the surface area of the liquid. However, when surfactants are added to the liquid, they adsorb at the liquid-air interface, disrupting the cohesive forces of the liquid molecules at the surface. This leads to a reduction in surface tension, causing the liquid to spread more easily and lowering the resistance to deformation of the liquid surface.

#### Energy needed to stop a reaction is referred to as

Activation energy is the minimum amount of energy that reactant molecules must possess to undergo a chemical reaction. It represents the energy barrier that reactants must overcome to reach the transition state, where new bonds are formed and old bonds are broken. Once the reactants reach the transition state and overcome the activation energy, the reaction proceeds spontaneously, and products are formed.

#### Using a sample that is white, you can see that there is absorption.

In optics and color perception, white light is composed of all colors of the visible spectrum. When light encounters a sample that appears white, it means that the sample is reflecting all the wavelengths of visible light and absorbing none. As a result, there is no absorption of any specific color or wavelength, and the absorption is 0%.

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

The relation between the amount of energy absorbed by a substance and its concentration is indeed given by Beer's law, also known as the Beer-Lambert law. Beer's law states that the absorbance (A) of a solution is directly proportional to the concentration (c) of the absorbing solute and the path length (l) of the light through the solution.

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

Concentration is a measure of the quantity of solute present in a given amount of solvent or solution. It describes how much of the solute is distributed in a specific volume of the solution. Concentration can be expressed in various units, such as moles per liter (mol/L or M), grams per liter (g/L), or percentage (%).

#### Choose the inaccurate composition percentage expression.

The expression m/d% is not a standard representation for percentage composition and is not commonly used in chemistry.

#### Which one compresses more easily?

In the gaseous state, the particles are widely spaced and have high kinetic energy, allowing them to move freely and independently. When pressure is applied to a gas, the volume of the gas can be significantly reduced because the gas particles can be easily compressed closer together. This is due to the large empty spaces between gas particles.

#### Pa is the SI unit for pressure. equivalent to

The Pascal is a derived unit of pressure in the International System of Units (SI). It is defined as the pressure exerted by a force of one Newton acting on an area of one square meter. Mathematically, it can be expressed as: 1 Pa = 1 N/m²

Pressure is a measure of force applied per unit area and is commonly used to describe various phenomena, such as atmospheric pressure, blood pressure, and pressure in engineering and physics applications.

#### The rate at which phenolphthalein fades in basic solution is

Phenolphthalein fading in basic solution does not follow second-order kinetics. The reaction is generally considered to be first-order with respect to phenolphthalein concentration. The fading of the pink color of phenolphthalein in a basic solution occurs due to its decomposition, which is typically described by first-order kinetics.

#### Choose the answer that has nothing to do with homogeneous mixture.

In the example "solution of sand in water," sand is not uniformly distributed throughout the water, and it forms a heterogeneous mixture. When sand is added to water, it does not dissolve or form a solution but rather remains separate, forming a suspension or a mixture with visible boundaries between the sand particles and water. Therefore, the example provided does not relate to a homogeneous mixture.

#### When an unsaturated solution is overconcentrated, it transforms into

When an unsaturated solution is concentrated up to its limit, it changes into a saturated solution. An unsaturated solution is a solution in which the solute is dissolved in the solvent, and more solute can still be dissolved at a given temperature. As more solute is added to the unsaturated solution, it can dissolve without causing any precipitation or saturation.

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

To calculate the percentage of the solution, we need to determine the total mass of the solution, which is the sum of the mass of solute (NaCl) and the mass of the solvent (H2O).

Given:
Mass of NaCl (solute) = 2 g

Mass of H2O (solvent) = 20 g

Total mass of the solution = Mass of NaCl + Mass of H2O

Total mass of the solution = 2 g + 20 g = 22 g

Now, we can calculate the percentage of the solution:

Percentage of solution = (Mass of NaCl / Total mass of the solution) × 100

Percentage of solution = (2 g / 22 g) × 100

Percentage of solution ≈ 9.09%

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

To prepare a 25 ml of 0.06 M solution from a 0.1 M stock solution, we can use the dilution formula:

C1V1 = C2V2

Where:

C1 = Initial concentration of the stock solution (0.1 M)

V1 = Volume of the stock solution required (unknown, we are trying to find this)

C2 = Final concentration of the diluted solution (0.06 M)

V2 = Final volume of the diluted solution (25 ml)

Now, plug in the values:

(0.1 M) V1 = (0.06 M) (25 ml)

Solving for V1:

V1 = (0.06 M) (25 ml) / 0.1 M

V1 = 15 ml

So, to prepare 25 ml of a 0.06 M solution, you need to take 15 ml of the 0.1 M stock solution and then add water to bring the total volume up to 25 ml. Therefore, the correct answer is 15 ml.