Exactly of a completely unknown mono-equivalent basic substance requires exactly of a standard acid — Mole Concept and Some Basic Concepts of Chemistry Chemistry Question
Question
Exactly $2.0\text{ g}$ of a completely unknown mono-equivalent basic substance requires exactly $100\text{ mL}$ of a $0.4\text{ N}$ standard acid solution to reach the theoretical endpoint of neutralization. Calculate the exact equivalent weight of this unknown base.
💡 Solution & Explanation
Step 1: Apply the fundamental Law of Chemical Equivalence. At the neutralization endpoint, the number of gram equivalents of the base must exactly equal the number of gram equivalents of the acid. Step 2: Formulate the equivalents. Equivalents of the unknown base = $\frac{\text{Mass}}{\text{Equivalent Weight}} = \frac{2.0}{E}$. Equivalents of the acid = $\text{Normality} \times \text{Volume in Liters} = 0.4 \times \left(\frac{100}{1000}\right) = 0.4 \times 0.1 = 0.04\text{ eq}$. Step 3: Equate and solve for E. $\frac{2.0}{E} = 0.04 \Rightarrow E = \frac{2.0}{0.04} = 50$.