Calculation of Equivalent Mass of Metal

Given:
- Mass of metal = 3g
- Volume of hydrogen gas liberated = 2800 cm³
- Pressure = STP

Step 1: Calculation of moles of hydrogen gas
- Using the ideal gas equation: PV = nRT
- At STP, pressure (P) = 1 atm, volume (V) = 2800 cm³, temperature (T) = 273 K, and R = 0.0821 L atm/mol K
- n = PV/RT = (1 atm x 2800 cm³) / (0.0821 L atm/mol K x 273 K)
- n = 0.108 mol

Step 2: Calculation of equivalent mass of metal
- The equivalent weight of a substance is the amount of it that reacts with or replaces one mole of hydrogen ions (H⁺) in an acid-base reaction
- In this case, the metal reacts with HCl to produce H₂ gas
- The balanced chemical equation is: 2HCl + M → MCl₂ + H₂
- Therefore, one mole of metal (M) reacts with two moles of HCl to produce one mole of H₂
- From the given information, 3g of metal reacts with 2800 cm³ of H₂ gas at STP
- Using the molar mass of H₂ (2 g/mol), we can calculate the number of moles of H₂ produced: n(H₂) = 2800 cm³ x (1 L/1000 cm³) x (1 mol/22.4 L) = 0.125 mol
- Since one mole of metal reacts with one-half mole of H₂, the number of moles of metal is: n(M) = 0.125 mol/2 = 0.0625 mol
- The equivalent weight of the metal is then calculated as: equivalent weight = (mass of metal) / (moles of metal)
- equivalent weight = 3g / 0.0625 mol = 48 g/mol

Step 3: Conclusion
- The equivalent weight of the metal is calculated to be 48 g/mol.