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51. One mole of H₂SO₄ should completely react with two moles of NaOH. How does Avogadro’s number help to explain it?

One mole of H₂SO₄ produces two moles of H⁺ ions (2N_A) while one mole of NaOH produces only one mole of OH^– ions (1N_A), therefore, one mole of H₂SO₄ can neutralize two moles of NaOH. The reaction is as follows.
H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

OR
1 mole of H₂SO, when completely ionizes produces two moles of H ions or 2 x 6.02 x 10²³ ions. Two moles of NaOH also produce two moles of OH- ions or 2 x 6.02 x 1023 ions. When these solutions are mixed together, they have an equal number of H+ and OH- ions and the solution becomes neutral.

52. Differentiate between ion and molecular ion?

Ion

Ions are those species which carry either positive or negative charge/charges. Whenever an atom of an element loses one or more electrons positive ions are formed, these are called cations. For example, Na+, Ca2+, Mg2+ etc. But when a neutral atom picks up one or more electrons, a negative ion is produced which is called an anion. For example, F^–, CI^–, Br^–, S^2- etc.

Molecular Ion

When a molecule loses or gain an electron to form a molecular ion e.g., CH4⁺, CO⁺, N₂⁺ etc.

53. Define cation and anion.

Cation:

Whenever an atom of an element loses one or more electrons positive ions are
formed these are called cations. For example, Na⁺, Ca²⁺, Mg²⁺ etc.

Anion:

when a neutral atom picks up one or more electrons a negative ion is produced which is called an anion. For example, F^–, CI^–, Br^–, S^2- etc.

54. What are isotopes? Why do they have the same chemical but different physical properties?

Atoms of the same elements can possess different atomic masses but the same atomic numbers, such atoms of an element are called isotopes. For example, carbon has three isotopes written as C-12, C-13 and C-14.

Isotopes of an element have the same chemical properties and the same position in the periodic table, but due to different atomic masses, have different physical properties.

55. What is the percentage yield? Give its significance.

A chemist is usually interested in the efficiency of a reaction. The efficiency of a reaction is expressed by comparing the actual and theoretical yields in the form of percentage yield.

56. Differentiate between actual (Experimental) yield and theoretical yield?

Yield

The amount of the products obtained in a chemical reaction is called the yield of that reaction.

Theoretical yield or calculated yield.

The amount of the products calculated from the balanced chemical equation represents the theoretical yield or calculated yield. The theoretical yield is the maximum amount of the product that can be produced by a given amount of a reactant, according to the balanced chemical equation.

Experimental yield or Actual yield.

The amount of the product which is actually obtained after performing an experiment is called experimental yield or actual yield.

57. Define mole and molar volume?

Mole
The atomic mass of an element or molecular mass of a molecule and the formula mass of a formula unit expressed in grams is called gram atomic mass, gram molecular mass and gram formula unit mass respectively. These are also called gram moles or simply moles.

Molar Volume
One mole of a gas at standard temperature and pressure (STP) occupies a volume of 22.414 dm³ is called molar volume and it is true only when the gas is ideal.

58. How many oxygen atoms are present in 4.8g of Ozone (O =16 a.m.u)?

59. What is the function of an ionization Chamber in a Mass Spectrometer?

Vapours are allowed to enter the ionization chamber where fast-moving electrons are thrown upon them. The atoms of isotopic elements present in the form of vapours are ionized. These positively charged ions of isotopes of an element have different masses depending upon the nature of the isotopes present in them.

If you want to prepare the theory section of Chapter 1 (Chemistry notes) Then it is here