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Q1. The mass of substance depends on the number of
The mass of a substance depends on the number of particles (atoms, molecules, or ions) it contains. For example, the more atoms an element has, the greater its mass. This is why the mole concept is useful—it connects the number of particles to the mass of a substance. Protons, electrons, and charges affect atomic structure, but the overall mass depends on the number of particles.
Q2. The unit mole was officially accepted in the year
The unit mole was officially accepted in the year 1967. The mole became an SI base unit during the 14th General Conference on Weights and Measures (CGPM) in 1971, but it was formally proposed and accepted in 1967. This standardised the mole as a unit for measuring the amount of substance.
Q3. The number of moles in 52 g of He is
The number of moles in 52 g of He is 13. The molar mass of helium (He) is 4 g/mol (atomic mass of He is 4 u). Number of moles = Given mass / Molar mass = 52 g / 4 g/mol = 13 moles. This shows how the mole concept helps convert mass to moles.
Q4. 6.022 × 10²³ molecules of N₂ represent
6.022 × 10²³ molecules of N₂ represent one mole. This is Avogadro’s number, and it is the number of particles in one mole of any substance. Whether it is molecules of N₂, atoms of carbon, or ions, one mole always contains 6.022 × 10²³ entities.
Q5. One mole of water contains
One mole of water contains 6.022 × 10²³ molecules of water. This is Avogadro’s number. It is the number of water molecules in 18 g of water (since the molecular mass of water is 18 u). This is a fundamental constant in chemistry.
Q6. The word “mole” is derived from the Latin word
The word “mole” is derived from the Latin word “moles,” which means a heap or pile. This is fitting because a mole represents a large collection (heap) of particles—6.022 × 10²³ of them. The word “molecule” comes from the same root, meaning a small mass or heap.
Q7. The Latin word “moles” means
The Latin word “moles” means a heap or pile. This is the origin of the word “mole” in chemistry. It signifies a collection of a very large number of particles, just as a heap consists of many individual pieces. The mole is essentially a convenient way to count a huge number of atoms or molecules.
Q8. The molar mass of helium is
The molar mass of helium is 4 g/mol. Helium has an atomic mass of 4 u (atomic number 2, with 2 protons and 2 neutrons). Therefore, one mole of helium atoms weighs 4 grams. This makes helium one of the lightest elements.
Q9. A substance can be considered as a heap of
A substance can be considered as a heap of atoms or molecules. Matter is made up of atoms and molecules, and the mole is a way to count these microscopic entities as a macroscopic heap. A mole of any substance is a collection (heap) of 6.022 × 10²³ particles.
Q10. One mole is equal to
One mole is equal to the relative atomic or molecular mass of a substance expressed in grams. For example, the atomic mass of carbon is 12 u, so one mole of carbon weighs 12 grams. This relationship is why moles are so useful in chemistry.
Q11. 8 g of O₂ molecules correspond to
8 g of O₂ molecules correspond to 0.25 mole. The molar mass of O₂ is 32 g/mol (since the atomic mass of oxygen is 16 u, O₂ = 16 × 2 = 32 u). Number of moles = 8 g / 32 g/mol = 0.25 mol. This is a common calculation using the mole concept.
Q12. The atomic mass of helium (He) is
The atomic mass of helium (He) is 4 u (approximately 4.0026 u). Helium has an atomic number of 2 and is a noble gas with 2 protons and 2 neutrons. Its atomic mass is essential for calculating the molar mass of helium, which is 4 g/mol.
Q13. 100 g of sodium has
100 g of sodium has more atoms than 100 g of iron. Sodium has a lower atomic mass (23 u) compared to iron (56 u). For the same mass, the substance with lower atomic mass has more atoms because each atom is lighter. Therefore, 100 g of sodium contains more atoms than 100 g of iron.
Q14. The mass of 0.5 mole of nitrogen atoms is
The mass of 0.5 mole of nitrogen atoms is 7 g. The atomic mass of nitrogen is 14 u, so one mole of nitrogen atoms weighs 14 g. Half a mole weighs 0.5 × 14 = 7 g. Note that this is for nitrogen atoms (N), not nitrogen molecules (N₂).
Q15. A mole is called the chemist’s
A mole is called the chemist’s counting unit. Just as a dozen is 12 items, a mole is 6.022 × 10²³ particles. It allows chemists to count atoms and molecules on a macroscopic scale by weighing them. It is essentially a convenient way to count a very large number of particles.
Q16. If one mole of carbon weighs 12 g, then one atom of carbon weighs
If one mole of carbon weighs 12 g, then one atom of carbon weighs 12 ÷ 6.022 × 10²³ g. Since one mole contains Avogadro’s number of atoms, the mass of a single atom is the molar mass divided by Avogadro’s number. This is an extremely small mass, approximately 1.99 × 10⁻²³ g.
Q17. 18 g of water contains
18 g of water contains one mole of water molecules. The molecular mass of water (H₂O) is 18 u (2 × 1 + 16 = 18). Therefore, the molar mass of water is 18 g/mol. So 18 g of water is exactly 1 mole, which contains 6.022 × 10²³ water molecules.
Q18. Chemists need the number of atoms and molecules mainly for
Chemists need the number of atoms and molecules mainly for carrying out reactions. In chemical reactions, the ratio of reactants and products is determined by the number of atoms and molecules, not just their masses. The mole concept helps chemists determine the exact amounts of substances needed for reactions.
Q19. Mole helps in converting
The mole helps in converting mass to the number of particles. By knowing the molar mass of a substance, we can convert a given mass into the number of moles, and from moles to the actual number of atoms or molecules using Avogadro’s number. This is one of the most important applications of the mole concept.
Q20. The Avogadro number is
The Avogadro number is 6.022 × 10²³. This number represents the number of particles (atoms, molecules, ions) present in one mole of any substance. It is a fundamental constant in chemistry and is named after the Italian scientist Amedeo Avogadro.
Q21. The mole concept is mainly used in
The mole concept is mainly used in chemistry. It is essential for chemical calculations involving reactions, stoichiometry, and the composition of compounds. While it is also used in other sciences, chemistry relies on the mole concept more extensively than any other subject.
Q22. The number of particles is calculated by
The number of particles is calculated by multiplying the number of moles (n) by Avogadro’s number (NA). The formula is: Number of particles = n × NA. For example, if you have 2 moles of water, the number of water molecules is 2 × 6.022 × 10²³ = 1.2044 × 10²⁴.
Q23. The molar mass of nitrogen atom is
The molar mass of a nitrogen atom is 14 g/mol. Nitrogen has an atomic mass of 14 u (atomic number 7, with 7 protons and 7 neutrons). So one mole of nitrogen atoms weighs 14 grams. Nitrogen gas (N₂) has a molar mass of 28 g/mol.
Q24. The symbol of Avogadro number is
The symbol of Avogadro number is NA (with A as a subscript). This notation is used to represent the Avogadro constant, which has a value of 6.022 × 10²³ mol⁻¹. The ‘A’ stands for Avogadro. This symbol is used in various chemical calculations.
Q25. Number of moles is calculated using the formula
The number of moles is calculated using the formula n = m ÷ M, where ‘m’ is the given mass of the substance and ‘M’ is the molar mass. This is the fundamental equation of the mole concept. It allows us to convert from mass to moles and vice versa.
Q26. The word “mole” was introduced by
The word “mole” was introduced by the German chemist Wilhelm Ostwald. He used the term “mol” to describe the amount of substance in chemistry. Avogadro gave the concept, but it was Ostwald who introduced the word ‘mole’ to represent it.
Q27. The number of particles from mass is calculated using
The number of particles from mass is calculated using the formula: Number of particles = (Mass × Avogadro number) ÷ Molar mass. This combines the mass-to-mole conversion (mass ÷ molar mass) and the mole-to-particles conversion (moles × Avogadro number). This is useful for finding the actual number of atoms or molecules in a given mass.
Q28. The atomic mass of sodium (Na) is
The atomic mass of sodium (Na) is 23 u (approximately 22.99 u). Sodium has an atomic number of 11 and is a soft, highly reactive metal. Its atomic mass is used to calculate the molar mass of sodium (23 g/mol) and its compounds.
Q29. The number of molecules in 0.1 mole of carbon atoms is
The number of molecules in 0.1 mole of carbon atoms is 6.022 × 10²². Since one mole contains 6.022 × 10²³ atoms, 0.1 mole contains 0.1 × 6.022 × 10²³ = 6.022 × 10²² atoms. Carbon exists as atoms, not molecules (in diamond and graphite), but if referring to carbon atoms, this is the correct calculation.
Q30. The relation between mass and number of particles is done using the
The relation between mass and the number of particles is done using the mole concept. The mole concept provides a bridge between the microscopic world (atoms and molecules) and the macroscopic world (grams and kilograms). Through molar mass and Avogadro’s number, we can convert between mass and number of particles.
Q31. The mass of 0.5 mole of N₂ gas is
The mass of 0.5 mole of N₂ gas is 14 g. The molar mass of N₂ is 28 g/mol (since nitrogen’s atomic mass is 14 u, N₂ = 14 × 2 = 28 u). Therefore, 0.5 mole of N₂ weighs 0.5 × 28 = 14 g. This is a common calculation using the mole concept for gaseous substances.
Q32. The molar mass of nitrogen atom is
The molar mass of a nitrogen atom is 14 g/mol. The atomic mass of nitrogen is 14 u. Therefore, one mole of nitrogen atoms weighs 14 grams. The molar mass of nitrogen molecules (N₂) is 28 g/mol, but the molar mass of the atom is 14 g/mol.
Q33. The molar mass of O₂ molecule is
The molar mass of an O₂ molecule is 32 g/mol. Oxygen has an atomic mass of 16 u. Since O₂ is a diatomic molecule, its molecular mass is 16 × 2 = 32 u. Therefore, one mole of O₂ molecules weighs 32 grams. This is the oxygen we breathe.
Q34. The atomic mass of iron (Fe) is
The atomic mass of iron (Fe) is 56 u (approximately 55.85 u). Iron has an atomic number of 26 and is a transition metal. Its atomic mass is essential for calculating the molar mass of iron and its compounds. 56 u makes iron about twice as heavy as aluminium (27 u).
Q35. The molar mass of nitrogen molecule (N₂) is
The molar mass of a nitrogen molecule (N₂) is 28 g/mol. Nitrogen has an atomic mass of 14 u, and since N₂ consists of two nitrogen atoms, its molecular mass is 14 × 2 = 28 u. Therefore, one mole of N₂ molecules weighs 28 grams.
Q36. 18 u of water contains
18 u of water contains one molecule of water. The molecular mass of water (H₂O) is 18 u. Therefore, a single molecule of water has a mass of 18 u. This is the microscopic mass of one water molecule. One mole of water molecules weighs 18 grams.
Q37. 46 g of sodium contains how many atoms?
46 g of sodium contains 1.2044 × 10²⁴ atoms. The atomic mass of sodium is 23 u, so its molar mass is 23 g/mol. Number of moles = 46 g / 23 g/mol = 2 moles. Number of atoms = 2 × 6.022 × 10²³ = 1.2044 × 10²⁴ atoms. This shows how the mole concept helps count atoms.
Q38. The mass of 6.022 × 10²³ N₂ molecules is
The mass of 6.022 × 10²³ N₂ molecules is 28 g. This is because 6.022 × 10²³ molecules represent one mole of N₂. The molar mass of N₂ is 28 g/mol (since N₂ = 2 × 14 = 28 u). Therefore, one mole of N₂ molecules weighs 28 grams.
Q39. The SI unit of amount of substance is
The SI unit of amount of substance is the mole (mol). It is one of the seven base SI units. The mole is defined as the amount of substance that contains as many entities (atoms, molecules, ions) as there are atoms in 0.012 kg of carbon-12. This unit is essential for all chemical calculations.
Q40. 12.044 × 10²³ He atoms are equal to
12.044 × 10²³ He atoms are equal to 2 moles. One mole contains 6.022 × 10²³ atoms. Therefore, 12.044 × 10²³ / 6.022 × 10²³ = 2 moles. This calculation shows how to convert from the number of atoms to moles using Avogadro’s number.
Q41. The word “mole” was introduced around the year
The word “mole” was introduced around the year 1896 by Wilhelm Ostwald. He used the term to describe the amount of substance in chemistry. Before this, the concept existed but did not have a specific name. 1896 was the year Ostwald introduced the term in his textbook.
Q42. Avogadro number is named after
The Avogadro number is named after the Italian scientist Amedeo Avogadro. He proposed in 1811 that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. Although he did not calculate the number, his work led to the discovery of Avogadro’s number.
Q43. 3.011 × 10²³ nitrogen atoms represent
3.011 × 10²³ nitrogen atoms represent 0.5 mole. One mole contains 6.022 × 10²³ atoms. Therefore, 3.011 × 10²³ / 6.022 × 10²³ = 0.5 mol. This means half a mole of nitrogen atoms contains this many atoms.
Q44. Mole provides a simple way to report
The mole provides a simple way to report large numbers of particles. Since atoms and molecules are extremely small, counting them individually is impossible. The mole allows chemists to work with manageable numbers (like 1 mole instead of 6.022 × 10²³ particles) while still representing huge quantities of particles.
Q45. One mole of any substance contains
One mole of any substance contains the same number of particles—6.022 × 10²³. Whether it is a mole of carbon atoms, water molecules, or sodium ions, the number of particles is always Avogadro’s number. However, the mass, volume, and density of one mole vary from substance to substance.
Q46. The symbol used for number of moles is
The symbol used for the number of moles is ‘n’. This is the standard notation in chemistry. For example, if you have 2 moles of a substance, you write n = 2 mol. ‘m’ is used for mass, ‘M’ for molar mass, and ‘N’ for the number of particles.
Q47. The mass of 3.011 × 10²³ nitrogen atoms is
The mass of 3.011 × 10²³ nitrogen atoms is 7 g. This is half a mole of nitrogen atoms (since 3.011 × 10²³ is half of Avogadro’s number). The atomic mass of nitrogen is 14 u, so one mole weighs 14 g. Half a mole weighs 0.5 × 14 = 7 g.
Q48. Number of moles from particles is given by
The number of moles from particles is given by n = N ÷ NA, where N is the number of particles and NA is Avogadro’s number. This formula allows you to convert from the number of particles to moles. For example, if you have 6.022 × 10²³ molecules, n = 6.022 × 10²³ / 6.022 × 10²³ = 1 mole.
Q49. The number of moles can also be calculated using
The number of moles can be calculated using a given number of particles (atoms, molecules, or ions). The formula is n = Number of particles ÷ Avogadro’s number. Similarly, moles can be calculated from mass using n = m ÷ M. Both methods are commonly used.
Q50. The relationship between mass, mole and number is shown by
The relationship between mass, mole, and number is shown by the mole concept. The mole concept connects these three quantities: mass (in grams) can be converted to moles using molar mass, and moles can be converted to the number of particles using Avogadro’s number. This forms the foundation of stoichiometry in chemistry.