Stoichiometry (VSAQs)

Chemistry-1 | 5. Stoichiometry – VSAQs:
Welcome to VSAQs in Chapter 5: Stoichiometry. This page includes the important FAQs for Very Short Answer Questions. Each answer is provided in simple English and follows the exam format. This approach helps you focus on key details and secure top marks in your final exams.

VSAQ-1 : Calculate the Oxidation numbers of Oxygen in (i) O2 F2 (ii) OF2

Oxidation Numbers of Oxygen

  1. In O₂, the oxidation number of oxygen is 0 because it exists in its elemental form, and elemental oxygen always has an oxidation state of 0.
  2. In OF₂, the oxidation number of oxygen is -2. This is because fluorine (F) is more electronegative than oxygen, and in compounds, fluorine has an oxidation state of -1. Since there are two fluorine atoms in OF₂, they contribute a total of -2 to the molecule. To maintain overall charge neutrality, the oxidation state of oxygen is +2.

VSAQ-2 : Calculate the Oxidation numbers of chromium in (i) Cr2 O72 (ii) K2 Cr2 O7

Oxidation Numbers of Chromium

  1. In Cr₂O₇²⁻, chromium has an oxidation number of +6.
  2. In K₂Cr₂O₇, chromium has an oxidation number of +7.

VSAQ-3 : Calculate the Oxidation numbers of Mn in (i) KmnO4 (ii) K2 MnO4 (iii) MnO4^(-2)

  1. In KMnO₄, manganese (Mn) has an oxidation number of +7.
  2. In K₂MnO₄, manganese (Mn) has an oxidation number of +6.
  3. In MnO₄²⁻, manganese (Mn) has an oxidation number of +7.

VSAQ-4 : Assign Oxidation number to the underlined elements in (i) NaHSO4 (ii) H4 (P2 ) O7

  1. In NaH₂SO₄, sulfur (S) has an oxidation number of +6.
  2. In H₄(P₂O₇), phosphorus (P) has an oxidation number of +5.

VSAQ-5 : How many number of moles of glucose are present in 540 grams of glucose.

There are 3 moles of glucose present in 540 grams of glucose.

VSAQ-6 : How many no. of CaCO3 moles are present 200gms of CaCO3?

There are 2 moles of CaCO₃ (calcium carbonate) present in 200 grams of CaCO₃.

VSAQ-7 : Calculate the weight of 0.1 mole of Sodium carbonate.

The weight of 0.1 mole of sodium carbonate (Na₂CO₃) is 10.6 grams.

VSAQ-8 : The empirical formula of a compound is CH2O Its molecular weight is 90. Calculate the molecular formula of the compound.

The molecular formula of the compound is C₃H₆O₃.

VSAQ-9 : Calculate the molarity of NaOH in the solution prepared by dissolving 4 g in enough water to form 250 ml of the solution.

Molarity of NaOH Solution

  1. Calculate the number of moles of NaOH: Moles = Mass (g) / Molar mass (g/mol)The molar mass of NaOH (sodium hydroxide) is approximately 40 g/mol.Moles of NaOH = 4 g / 40 g/mol = 0.1 moles
  2. Calculate the volume of the solution in liters: Volume (L) = 250 ml / 1000 ml/L = 0.25 L
  3. Calculate the molarity (M) using the formula: Molarity (M) = Moles / Volume (L)Molarity (M) = 0.1 moles / 0.25 L = 0.4 M

So, the molarity of the NaOH solution is 0.4 M.

VSAQ-10 : What are disproportionation reactions? Give an example.

  1. Definition: These reactions involve a substance undergoing simultaneous oxidation and reduction, forming two different compounds with varying oxidation states.
  2. Example: Hydrogen peroxide (H₂O₂) decomposing into water (H₂O) and oxygen (O₂) is a disproportionation reaction.