Question

A piece of sodium metal reacts completely with water as follows 2Na(s) + 2H2O(l)+2NaOH(aq)+ H2(g) The hydrogen gas generated is collected over water at 25.0oC. The volume of the gas is 246 mL measured at 1.00 atm. Calculate the number of grams of sodium used in the reaction. (Vapor pressure of water at 25°C 0.0313 atm.)

Answer 1

Balanced equation:
2 Na(s) + 2 H₂O(l) ===> 2 NaOH(aq) + H₂(g)
Reaction type: single replacement

Vapor pressure of water at 25°C 0.0313 atm

PV = nRT

P = 1 = 0.0313 = 0.9687 atm

V = 246 ml or 0.246 Liter

n = Moles

R = 0.0821 L atm K-1 Mol-1

T = 273 + 25 = 298 K

calculate the Moles of H2

n = PV / RT

n = 0.9687 atm x 0.246 Liter / 0.0821 L atm K-1 Mol-1 x 298 K

n = 0.00974 Moles

Moles of Na reacted = 0.00974 Moles

Mass of sodium Used = 0.00974 x 22.989 = 0.222 gm