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

Concept:

Normality:

• It is defined as the number of grams equivalent per litre of solution.
• Also known as equivalent concentration.
• Normality = Number of gram equivalents / [volume of solution in litres]

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\({\rm{Normality}} = \frac{{{\rm{Gram\;equivalents}}}}{{{\rm{volume\;of\;solution\;in\;liter}}}}\)

\({\rm{No}}.{\rm{\;of\;gram\;equivalents}} = \frac{{{\rm{Given\;weight}}}}{{{\rm{Equivalent\;weight}}}}\)

\({\rm{And\;equivalent\;weight}} = \frac{{{\rm{Molecular\;weight}}}}{{{\rm{Valency}}}}\)

The Normality of a mixture of solutions is given by N₁v₁ + N₂V₂ + N₃V₃ + ..... = N_rV_r, where N₁, N₂, N₃ are the normality of the components and V₁, V₂, V₃ are their respective volumes.

N_r is the final normality and V_r is the volume of the resultant mixture or the solution.

Calculation:

Given:

Strength N₁ of H₂SO₄ = 10N

Volume V₁ of H2SO4 = 50 mL

Strength N1 of HCl = 12 N

Volume V₂ of HCl = 25 mL

Strength N₃ of HNO3 = 5N

Volume V₃ of HNO3 = 40 mL

Volume of the mixture = V_r = 1000 mL

Normality of the mixture = N_r =?

We know, The Normality of a mixture of solutions is given by N1V1 + N2V2 + N3V3 + ..... = NrVr

Hence,

10 × 50 + 12 × 25 + 5 × 40 = 1000 × N_r

or, N_r ×  1000 = (500 + 300 + 200) = 1000

or, N_r = 1000/1000 = 1.

Hence, the Normality of the final mixture is 1N.

Concept:

• Normality:
  • It is defined as the number of grams equivalent per liter of solution.
  • Also known as equivalent concentration.

​\({\rm{Normality}} = \frac{{{\rm{Gram\;equivalents}}}}{{{\rm{volume\;of\;solution\;in\;liter}}}}\)

\({\rm{No}}.{\rm{\;of\;gram\;equivalents}} = \frac{{{\rm{Given\;weight}}}}{{{\rm{Equivalent\;weight}}}}\)

\({\rm{And\;equivalent\;weight}} = \frac{{{\rm{Molecular\;weight}}}}{{{\rm{Valency}}}}\)

• Normality is inversely proportional to temperature.
• Unit of normality is g. equivalent. lit-1.

Molality:

• It is defined as the number of moles of solute per kilogram of solvent.
• Unit of Molality is the mole. Kg-1.

​\({\rm{Molality}} = \frac{{{\rm{Moles\;of\;Solute}}}}{{{\rm{Kilogram\;of\;solvent}}}}\)

Molarity:

• It is defined as the moles of a solute per liters of a solution.
• It is also known as the molar concentration of a solution.
• The unit of Molarity is the mole. lit-1.
• It is given by:

\(\frac{{Number\;of\;moles\;of\;solute}}{{Mass\;of\;solvent\left( {in\;g} \right)}} \times 1000\)

• Molarity is inversely proportional to volume.
• Molarity is inversely proportional to temperature.

Calculation:

Given:

Amount of NaOH = w  = 40g

Amount of solvent = 1000 gm H2O

• Molar mass(M) of NaOH = 23 + 16 + 1 = 40 
• ​Hence, no of moles of NaOH = 

\({w\over M} = {40 \over 40 } = 1\)

Hence, 1 mole of solute is present in 1000g of solvent. Hence, the solution is one molal.

Hence, a solution made of by dissolving 40 gm of NaOH in 1000 gm H2O is 1 molal.

The correct answer is 6.022 × 10²³.

Key Points

• Avogadro's constant, also known as Avogadro's number, is named after the Italian scientist Amedeo Avogadro.
• It is defined as the number of constituent particles (usually atoms or molecules) that are contained in one mole of a substance.
• The value of Avogadro's constant is 6.022 × 10²³ mol^-1.
• Avogadro's constant is a fundamental constant in chemistry and physics that allows chemists to count the number of atoms, ions, or molecules in a given sample.

Additional Information

• Avogadro's Law:
  • Avogadro's law states that equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.
  • This law provides the relationship between the volume of a gas and the amount of substance of the gas present.
• The Mole Concept:
  • The mole is a unit of measurement for the amount of substance in the International System of Units (SI).
  • One mole contains exactly 6.02214076 × 10²³ elementary entities (Avogadro's constant).
  • This concept is used to convert between the number of particles and the amount of substance.
• Importance in Chemistry:
  • Avogadro's constant is crucial for understanding and working with chemical reactions, as it allows chemists to determine the number of particles involved.
  • It is essential for calculations involving the ideal gas law, stoichiometry, and other chemical principles.
• Historical Context:
  • Amedeo Avogadro (1776-1856) was an Italian scientist who made significant contributions to molecular theory.
  • Avogadro's hypothesis, proposed in 1811, led to the eventual development of the concept of the mole and Avogadro's constant.

The correct option is: 2

Explanation: To determine the empirical formula of the acid, we perform the following steps:

Step 1: Calculate the moles of carbon from CO₂:

• The molecular weight of CO₂ is 44.01 g/mol.
• The moles of CO₂ produced:\( [ \text{Moles of CO}_2 = \frac{1.023 \text{ g}}{44.01 \text{ g/mol}} \approx 0.02325 \text{ mol}]\)
• Each mole of CO₂ corresponds to 1 mole of carbon: \([ \text{Moles of C} = \text{Moles of CO}_2 = 0.02325 \text{ mol} ]\)

Step 2: Calculate the moles of hydrogen from H₂O:

• The molecular weight of H2O is 18.02 g/mol.
• The moles of H₂O produced: \([ \text{Moles of H}_2\text{O} = \frac{0.418 \text{ g}}{18.02 \text{ g/mol}} \approx 0.0232 \text{ mol} ]\)
• Each mole of H₂O corresponds to 2 moles of hydrogen: \([ \text{Moles of H} = 2 \times \text{Moles of H}_2\text{O} = 2 \times 0.0232 \text{ mol} = 0.0464 \text{ mol} ]\)

Step 3: Calculate the mass of carbon and hydrogen:

• Mass of carbon:\( [ \text{Mass of C} = \text{Moles of C} \times \text{Atomic weight of C} \)

        = \(0.02325 \text{ mol} \times 12.01 \text{ g/mol} \approx 0.2791 \text{ g} ]\)​

• Mass of hydrogen:\( [ \text{Mass of H} = \text{Moles of H} \times \text{Atomic weight of H} \)
• \(0.0464 \text{ mol} \times 1.01 \text{ g/mol} \approx 0.0469 \text{ g} ]\)

Step 4: Calculate the mass of oxygen:

• Total mass of the acid sample = 0.454 g
• Mass of oxygen = Total mass - Mass of carbon - Mass of hydrogen: \([ \text{Mass of O} = 0.454 \text{ g} - 0.2791 \text{ g} - 0.0469 \text{ g} \approx 0.128 \text{ g} ]\)
• Moles of oxygen:\( [ \text{Moles of O} = \frac{\text{Mass of O}}{\text{Atomic weight of O}} = \frac{0.128 \text{ g}}{16.00 \text{ g/mol}} = 0.008 \text{ mol} ]\)

Step 5: Determine the empirical formula:

• Moles of C: 0.02325
• Moles of H: 0.0464
• Moles of O: 0.008

Normalize the moles by the smallest number of moles calculated:

• \( [ \text{Ratio of C} = \frac{0.02325}{0.008} \approx 2.91 \approx 3 ] \)
• \([ \text{Ratio of H} = \frac{0.0464}{0.008} \approx 5.8 \approx 6 ]\)
• \( [ \text{Ratio of O} = \frac{0.008}{0.008} = 1 ]\)

The simplified molar ratio is approximately: C : H : O = 3 : 6 : 1

Thus, the empirical formula of the acid is\( ( \text{C}_3\text{H}_6\text{O} ).\)

The correct answer is 18 g.

Key Points

Explanation:

• 0.1 mole of C₆H₁₂O₆ = Molecular mass of C6H12O6 in grams
  • 0.1 (Mass of 6C + Mass of 12H + Mass of 6O)
  • 0.1 (12 × 6 + 1 × 12 + 16 × 6)
  • 0.1 (72 + 12 + 96)
  • 18 grams

• The correct answer is option 4, i.e., 1 mole of Carbon will contain the same number of atoms as present in 1 mole of Helium.
• Out of the given options, the correct statement is: 1 mole of Carbon will contain the same number of atoms as present in 1 mole of Helium.
• A mole is the SI unit of measurement for the amount of substance. 
• 1 mole = 6.022 x 10²³
• 1 mole of any particle has 6.022 x 1023 of that particle. For eg: 1 mole of atom = 6.022 x 1023 atoms, 1 mole of molecule = 6.022 x 1023 molecule, etc.
• 6.022 x 1023 is known as the Avagadro number.
• A mole does not depend on the atomic number, it's just a unit.
• Thus, 1 mole of Carbon and 1 mole of Helium will contain the same number of atoms i.e. 6.022 x 1023 atoms.

Step 1: Finding Atomic Mass:

The atomic mass of hydrogen = 1u

The atomic mass of oxygen = 16u

Molecular mass of water (H2O) = 2 × 1 + 1 × 16 = 18 u

Hence, the Molecular mass of 2 molecules of water = 36 u

Step 2: Concept of Avagadro Constant:

One mole of water contains 6.023 × 10²³ water molecules.

Now,

Mass of water molecule for 36 u = \(\frac{36}{6.023\times 10^{23}}\) = 5.98 × 10-23 g

Concept:

• The total number of moles of a compound divided by the total number of moles of all constituents gives us mole fraction.
• Mathematically, it can be expressed as:

\({X_1} = \;\frac{{no.\;of\;moles\;of\;sustance\;1}}{{total\;number\;of\;moles\;in\;the\;solution}}\)

Calculate Mole Fractions
For each component (A, B, C), the mole fraction \(X\) is calculated as:
\( X_{\text{A}} = \frac{\text{moles of A}}{\text{total moles}} = \frac{0.2}{0.6} = \frac{1}{3} \)
\( X_{\text{B}} = \frac{\text{moles of B}}{\text{total moles}} = \frac{0.2}{0.6} = \frac{1}{3}\)
\( X_{\text{C}} = \frac{\text{moles of C}}{\text{total moles}} = \frac{0.2}{0.6} = \frac{1}{3} \)

Sum of all mole fraction of all = 1/3 +1/3 + 1/3 = 1

• The total mole fraction of a solution always adds up to 1.

\(\sum {X_i = 1} \)

Mole fraction unit is very useful in relating some physical properties of solutions, says vapour pressure with the concentration of the solution and quite useful in describing the calculations involving gas mixtures.

Formula -

Mole Fraction = Moles of one component / Total moles of all component 

X_A+X_B+X_C = (N_A/ N_A+N_B+N_C) + (N_B/ NA+NB+N_C) + (N_C/ NA+NB+N_C) = 1

The correct answer is Increase.

Concept:

• Molarity:
  • It is defined as the moles of a solute per litres of a solution.
  • It is also known as the molar concentration of a solution.
• Molality:
  • It is defined as the number of moles of solute per kilogram of solvent.
• Mole fraction:
  • It is the ratio of moles of a component with the total moles of solute and solvent.
• Mass%:
  • It is the percentage of the mass of solute or solvent w.r.t total mass of solution.
• Formulas:

Explanation:

• Molarity depends on the volume of the solution.
• And volume is directly proportional to temperature.
• And when we increase the temperature the volume will increase.
• So the increase in volume leads to a decrease in Molarity as Molarity is inversely proportional to the volume of solution.

​Additional Information

Notes:

• Normality:
  • It is defined as the number of gram equivalent per litre of solution.
  • Also known as equivalent concentration.
  • Normality = Number of gram equivalents / [volume of solution in litres]
• Normality is inversely proportional to temperature.
• ​Volume is directly proportional to temperature.
• Molarity is inversely proportional to volume.
• Molarity is inversely proportional to temperature.
• Molality is not dependent on temperature.

The correct answer is 35.2 g.

Key PointsAtomic mass of sulphur =32

Mass of 1.1 mol of sulphur = 32*1.1= 35.2 g

Explanation:

• Combustion is a chemical reaction in which a substance reacts quickly with oxygen and produces heat.
• The original substance is referred to as the fuel, and the source of oxygen is referred to as the oxidizer.
• The fuel can take the form of a solid, liquid, or gas.

The Combustion equation for glucose is given as follows;

C₆H₁₂O₆ +6O₂ → 6CO₂  + 6H₂O

From the above balanced equation we can see that,

For complete combustion of 1 mole of glucose we need 6 mole of oxygen gas.

Hence, The number of moles of oxygen gas used in the complete combustion of 1 mole of glucose is 6

The correct answer is 13.

Concept:

• Mole: One mole is the amount of a substance that contains as many particles or entities as there are atoms in exactly 12 g (or 0.012 kg) of the 12C isotope.

Calculation:

• The number of moles in 52 g of He is 1
• \(Number~of~ moles = {Mass~ of~ substance \over Mass~ of~ one ~mole}\)
• The molar mass of helium gas is 4g/mol.
• Given the number of moles of substance=52g
• \(Number of moles = {52 \over 4}\)

The number of moles= 13g.

Hence the moles present in the 52g of He are 13Additional Information

• Helium:
  • It is a noble gas.
  • It is used for filling balloons and other lighter aircraft.
  • Helium (He), when mixed with O₂, is used by deep-sea divers for breathing and for respiratory patients.

Concept:

Mole Concept -

•  The quantity one mole of a substance signifies 6.022 × 1023 number of particles of that substance which may be atoms, molecules, or ions.
• The quantity is a universal constant like Dozen, Gross, etc., and is known as Avogadro number, denoted by NA. after the scientist Amedeo Avogadro.
• Examples- In one mole of H2, there are 6.022 × 1023 molecules of hydrogen, and the number of atoms is 2 × 6.022 × 1023, as one molecule of hydrogen contains two-atom each.
• The mass of one mole of a substance is called its Molar Mass (M) or Atomic mass expressed in grams.
• The volume occupied by a mole of gas is 22.4 L at NTP, called its Molar Volume.
• The no. of moles (n) is calculated as =

Number of particles / Avogadro’s number.

To summarise, we can say, 

Calculation:

Given: 

Mass of Oxygen molecule O₂ = 8g

• Molar mass of O₂ = 16 + 16 = 32g
• The number of moles of O₂ in 8g of O₂ =

8/32 = .25 moles 

• 1 mole contains =  6.022 × 1023 number of O2 molecules.
• Then .25 mole will contain =  

6.022 × 1023 × .25 = 1.51 × 1023

Hence, the number of particles in 8g of O2 molecules is 1.51 × 1023.

Given:

Mass of common salt (solute) = 41 g

Mass of water (solute) = 320 g

Formula Used:

Concentration of solution = (mass of solute / mass of solution) × 100

calculation:

according to the question

mass of solution = mass of solute + mass of solute

⇒ (41 + 320) g

⇒ 361 g

Now,

Concentration of solution = (mass of solute/mass of solution) × 100

(41/361 × 100)%

⇒ 11.357% ~ 11.36%

The required solution is 11.36%