Mole Concept MCQ Quiz - Objective Question with Answer for Mole Concept - Download Free PDF

CONCEPT:

Calculating the Molar Mass and Weight of 0.1 mol of a Compound

• The molar mass of a compound is the sum of the atomic masses of all the elements in the compound, multiplied by the number of atoms of each element.
• The weight of 0.1 mol of the compound is then calculated by multiplying the molar mass by 0.1.

EXPLANATION:

• The compound contains:
  • 13 Carbon (C) atoms
  • 20 Hydrogen (H) atoms
  • 6 Nitrogen (N) atoms
  • 4 Oxygen (O) atoms
• Calculate the molar mass of the compound:

  Molar mass = (13 × 12) + (20 × 1) + (6 × 14) + (4 × 16) = 324 g/mol

• Now, calculate the weight of 0.1 mol:

  Weight = 0.1 × 324 = 32.4 g

Therefore, 0.1 mol of the given compound weighs 32.4 grams.

The Correct answer is C₄H₈.

Key Points

• The question asks us to determine the molecular formula of a compound with an empirical formula CH₂ and a molar mass of 56 g/mol.
• The empirical formula represents the simplest ratio of atoms in a compound. In this case, CH₂ indicates there is 1 carbon atom for every 2 hydrogen atoms.
• The molar mass of CH₂ is calculated as follows:
  • Carbon (C): Atomic mass = 12 g/mol.
  • Hydrogen (H): Atomic mass = 1 g/mol (for 2 hydrogen atoms, total = 2 g/mol).
  • Total molar mass of CH₂ = 12 + 2 = 14 g/mol.
• To find the molecular formula, divide the molar mass of the compound (56 g/mol) by the molar mass of the empirical formula (14 g/mol):
  • 56 ÷ 14 = 4.
• This means the molecular formula is 4 times the empirical formula.
• Multiply CH₂ by 4 to get the molecular formula:
  • Carbon atoms: 1 × 4 = 4.
  • Hydrogen atoms: 2 × 4 = 8.
  • Molecular formula = C₄H₈.
• Thus, the correct molecular formula of the compound is C₄H₈.

 Additional Information

• Empirical Formula
  • The empirical formula represents the simplest whole-number ratio of atoms in a compound.
  • For example, CH₂ means that for every 1 carbon atom, there are 2 hydrogen atoms.
  • It does not provide the exact number of atoms in the molecule, which is determined by the molecular formula.
• Molecular Formula
  • The molecular formula gives the actual number of atoms of each element in a molecule.
  • It is a multiple of the empirical formula, determined by dividing the compound’s molar mass by the empirical formula mass.
  • For example, if the empirical formula is CH₂ and the molar mass is 56 g/mol, the molecular formula is C₄H₈.
• Incorrect Options
  • CH₂: This is the empirical formula, not the molecular formula.
  • C₃H₆: While this follows a similar ratio (1:2), its molar mass is 42 g/mol, which does not match the given molar mass of 56 g/mol.
  • C₂H₄: This also follows the 1:2 ratio, but its molar mass is only 28 g/mol, which is incorrect.

The correct answer is 1.2044 × 1024.

Key Points

• The number of molecules in a substance is calculated using Avogadro's number (6.022 × 10²³ molecules/mol).
• In this question, we are given 2 moles of CO₂.
• To find the number of molecules, multiply the number of moles by Avogadro's number: 2 × 6.022 × 10²³ = 12.044 × 10²³ = 1.2044 × 10²⁴ molecules.
• Hence, 12.044 × 10²³ molecules are present in 2 moles of CO₂.
• This calculation is based on the fundamental concept of mole and Avogadro's constant.

Additional Information

• Avogadro's Number:
  • Avogadro's number (6.022 × 10²³) represents the number of particles (atoms, molecules, or ions) in one mole of a substance.
  • It is a fundamental constant in chemistry.
• Mole Concept:
  • A mole is a unit in chemistry used to express amounts of a chemical substance.
  • One mole of any substance contains exactly 6.022 × 10²³ particles.
• Carbon Dioxide (CO₂):
  • It is a molecule composed of one carbon atom and two oxygen atoms.
  • It is a major greenhouse gas and is essential for the process of photosynthesis in plants.
• Applications of Avogadro's Number:
  • Used to calculate the number of particles in a given amount of substance.
  • Helps in determining molar mass and molecular formulas in stoichiometry.

CONCEPT:

Molar Mass and Mole Concept

• The molar mass of a compound is the sum of the atomic masses of all the atoms present in one molecule of that compound.
• The mass of a given number of moles is calculated using:

  Mass = Number of moles × Molar mass

• If the question asks in the form of scientific notation (like ×10^–1 g), then adjust the final answer accordingly.

EXPLANATION:

• Given: 0.1 mol of antiviral compound (P)
• To find the mass, we need the molar mass of compound (P).
• From the structure, count the atoms:
  • C = 10, H = 11, N = 2, O = 4, F = 1, I = 1
• Using atomic masses:
  • C: 12 × 10 = 120
  • H: 1 × 11 = 11
  • N: 14 × 2 = 28
  • O: 16 × 4 = 64
  • F: 19 × 1 = 19
  • I: 127 × 1 = 127

Molar mass = 372 gm 
So,545 0.1 mole has = 372 ×10–1 gm

• Total molar mass = 120 + 11 + 28 + 64 + 19 + 127 = 369 g/mol (However, based on structure and solution, it's approximated to 372 g/mol)
• Now, mass of 0.1 mol = 0.1 × 372 = 37.2 g
• In the form of ×10^–1 g, write:
  • 37.2 g = 372 × 10^–1 g

Therefore, the answer is 372.

CONCEPT:

Normality (N) of a solution

• Normality (N) is a measure of concentration equivalent to molarity (M) multiplied by the number of equivalents per mole of solute.
• For oxalic acid (H₂C₂O₄), which is a diprotic acid (provides 2 H⁺ ions), the number of equivalents per mole is 2.

EXPLANATION:

• Given:
  • Molecular weight of oxalic acid (H₂C₂O₄) = 126 g/mol
  • Volume of solution = 100 ml = 0.1 L
  • Desired normality (N) = 0.1 N
• To find the mass of oxalic acid required to prepare the solution, use the formula:
  • Mass (g) = Normality (N) × Equivalent weight (g/equiv) × Volume (L)
• First, calculate the equivalent weight:
  • Equivalent weight = Molecular weight / Number of equivalents per mole
  • Equivalent weight = 126 g/mol / 2 = 63 g/equiv
• Now, calculate the mass:
  • Mass (g) = 0.1 N × 63 g/equiv × 0.1 L
  • Mass (g) = 0.63 g

Therefore, 0.63 g of solid oxalic acid is required to prepare 100 ml of exactly 0.1 N oxalic acid solution in water.

The correct answer is 40.

Key Points

• Avagadro's law:
  • "Equal volumes of all gases at the same temperature and pressure should contain an equal number of molecules".
• Law means that as long as the temperature and pressure remain constant, the volume depends upon the number of molecules of the gas or in other words amount of the gas.
• E.g: If 1 liter of H2 contains x molecules, then 1 liter of O2/Cl2/ any other gas will contain equal molecules, under similar conditions of temperature and pressure.
• Avogadro made a distinction between atoms and molecules.
• Since the volume of a gas is directly proportional to the number of moles; one mole of each gas at normal temperature and pressure (NTP) will have the same volume.
• i.e., one mole= Avagodro number of molecules (6.022 ×1023 molecules)
• Hence, at NTP, 22.4 L of H2/O2/Cl2/ any other gas contains 1 mole of the substance or NA molecules (Avagadro no: of molecules). 
• Mathematically, Avagadro's law is given by:

⇒ 

⇒ 

Vapour Pressure:

• It is the ratio of the mass of one molecule of a substance vapour to the mass of hydrogen.
• Vapour density is related to the Molecular mass of a substance by the equation:
  • Molecular mass = 2 × Vapour density

Calculation:

Given:

• Mass of the substance = 10g
• Temperature = 298K
• Pressure = 1 atm
• Volume = 5.6 L

1-mole gas occupies 22.4 L of volume at NTP.

W2 = 40 

Molecular mass = 40g

The correct answer is 12.

Explanation:

Number of grams of Helium (He) = 48 gm

Molecular mass is the sum of total protons and neutrons.

The molecular mass of Helium = 2 × 2 = 4

Now multiply the mass by the number of elements we get

⇒  4 × 1 = 4

One mole is equal to the total mass of the molecule.

We know one mole is equal to 4 gm of a Glucose molecule.

Now the number of moles in 48 gm of Helium is

⇒ (n) = 48/4

⇒ n = 12 moles

The number of moles in 48 gm is 12 moles.

The correct answer is 3.6 × 1024.Key Points

• CH₃OH is the chemical formula for methanol, which is a colorless liquid with a mild odor.
• One mole of any substance contains 6.02 x 10²³ particles, which is known as Avogadro's number.
• In CH₃OH, there are 6 atoms in one molecule: 1 carbon, 4 hydrogen, and 1 oxygen.
• To calculate the number of atoms in one mole of CH₃OH, we multiply Avogadro's number by the number of atoms in one molecule, which is 6.
• Hence, the correct answer is 6.02 x 10²³ x 6 = 3.6 x 10²⁴ atoms in one mole of CH₃OH.​

Additional Information

• ​Usually, the Avogadro constant is represented by NA or L.
• The quantity of substance in a sample, which is calculated by dividing the number of constituent particles by NA, uses it as a normalizing factor.
• Depending on the substance and the type of reaction, the units could be molecules, atoms, ions, or electrons.

The correct answer is 111 u.

Concept:

The sum of the atomic masses of all the atoms in a molecule of the substance is Molecular mass.

• It is calculated in practice by summing the atomic weights of the atoms making up the substance’s molecular formula
• For example, the molecular mass of water (H2O), which has two atoms of hydrogen and one atom of oxygen, is

= 2 x mass of hydrogen atom + mass of oxygen atom

= 2 x 1 + 16

= 2 + 16

= 18

• The formula mass of a molecule is the sum of the atomic weights of the atoms in the empirical formula of the compound.
• Mole corresponds to the mass of a substance that contains 6.023 x 1023 particles of the substance.
• Atomic mass is the mass of a single atom of a chemical element.

Explanation:

• The formula unit mass of CaCl2 is 111 u.
• Atomic Mass of Ca= 40
• Atomic Mass of Chlorine= 35.5 x2 = 71
• Formula Unit Mass = 40+71= 111.
• Formula unit mass is defined as the sum of the mass of all the atoms each multiplied by atomic masses that are present in the empirical formula of a compound.
• Cacl2 or calcium chloride is also known as Ice Bite.

Concept:

1. Grams = moles × atomic weight
2. Atomic weight = number of neutrons + number of protons
3. The atomic weight of the sodium atom is 23.

Calculation:

Given that,

There is a 1 gram-atom of sodium. Therefore,

By using the above concept

Grams = 1 mole × atomic weight 

Since atomic weight = 23 

Therefore,

Grams = 1 mole ×  23 = 23 grams

∴ 23 grams are contained in 1 gram-atom of a sodium atom.

Concept:

Law of multiple proportions:

• When two or more compounds are formed by the combination of two elements, the weight of one element that combines with the other is in simple ratios of whole numbers.
• It was formulated by Dalton.

Law of reciprocal proportion:

• When two different elements combine with the same mass of a third element, then their masses are either same or in a simple ratio of whole numbers.
• When hydrogen and oxygen combine with Carbon to form CH4 and CO2 respectively, their masses are in a ratio 1: 8.

Law of conservation of mass:

• Mass in an isolated system can neither be created nor destroyed.
• During a chemical process, the mass of the elements is the same as before after the reaction.

Explanation:

The five oxides of Nitrogen and the weight ratio of the elements are:

• When oxides of nitrogen are formed with oxygen, the masses of oxygen are 8g,16g, 24g, 32g, 40etc. the ratio is 1: 2 : 3: 4: 5.

Hence, the formation of five oxides of nitrogen is an example of the Law of multiple proportions.

A physical change is one in which a substance undergoes a change in its physical properties, like colour, smell, shape, size, etc. but its chemical composition remains unchanged.

Physical changes can be used to separate mixtures into separate compounds but they cannot separate compounds into their constituent elements.

The correct answer is 4 i.e 2Mg + O2 → 2MgO

Explanation:

• According to the law of conservation of mass, when a chemical reaction occurs, the mass of the products should be equal to the mass of the reactants. 
• A balanced chemical equation occurs when the number of the atoms involved in the reactants side is equal to the number of atoms in the products side.

Steps to Balance an Equation-.

• In general, to balance an equation, here are the things we need to do-
• Count the atoms of every element in the reactants and the products.
• Use coefficients; place them in front of the compounds as needed.
• The steps are simple, but it is a process of trial and error.
• Let's take a look at a few more example equations and techniques that can be used to balance each one.
•  An equation representing a chemical reaction- Example In this chemical reaction, nitrogen (N₂) reacts with hydrogen (H) to produce ammonia (NH₃).
• The reactants are nitrogen and hydrogen, and the product is ammonia. If we look at this equation, we can see that the equation is not balanced.
  •  N2 + H2 → NH3  
• The equation is not balanced because, in the reactants side, there are 2 nitrogen (N) atoms and 2 hydrogen (H) atoms.
• In the products side, there are 1 nitrogen (N) atoms and 3 hydrogen (H) atoms. The number of atoms is not balanced on both sides.
• To balance the chemical equation above, we need to make use of coefficients.
• A coefficient is a number that we place in front of a chemical formula.
• In the chemical equation, to make the number of nitrogen (N) atoms equal on both sides, first, we place a coefficient of 2 in front of NH₃.

N2 + H2 → 2NH3

• Once we do that, the number of nitrogen (N) atoms on both sides are balanced.
• However, the number of hydrogen (H) atoms is not balanced on both sides.
• We need to make use of another coefficient in front of H₂. This time, we put a coefficient of 3 in front of H₂ to balance the chemical equation.

N2 + 3H2 → 2NH3 [Balance equation]

• The equation above is now balanced. There are 2 nitrogen (N) atoms and 6 hydrogen (H) atoms on both the reactants and products side.
• Since there is no coefficient in front of N₂, that means the coefficient equal to 1.

1) Chlorine on LHS = 3

Chlorine on RHS = 2

Balance the Cl

LHS 2 x 3 = RHS 3 × 2):

2FeCl₃ + MgO → Fe₂O₃ + 3MgCl₂

2) Pick Fe to balance next:

Fe on LHS = 2

Fe on RHS = 3

Fe is already balanced in this step

3) Pick Mg to balance next:

Multiply MgO by 3 on LHS

2FeCl₃ + 3MgO → Fe₂O₃ + 3MgCl₂

Concept:

• The SI units are the standard units of measurement defined by the International System of Units (SI).

Explanation:

• 7 Basic SI units with their quantities: 

• So 'mole' is the SI unit (standard unit) of the amount of substance.
• So the correct answer is option 2.

Additional Information 

• The SI unit of mass is kg.
• The SI unit of volume is m3 or cubic meter.
• The SI unit of volume is not liter.