Sodium hydride reacts with excess water to produce aqueous sodium hydroxide and hydrogen gas: NaH (s) + H₂O (l) → NaOH (aq) + H₂ (g)
A sample of NaH weighing ________ g will produce 982 mL of gas at 28.0 °C and 765 torr,when the hydrogen is collected over water.The vapor pressure of water at this temperature is 28 torr.

Question

Quizplus · Accepted Answer

First, calculate the pressure of dry hydrogen gas: 765 torr - 28 torr = 737 torr. Convert this to atm: 737/760 = 0.970 atm. Use the ideal gas law (PV=nRT) to find moles of H2: n = PV/RT = (0.970 atm)(0.982 L)/(0.0821 L·atm/mol·K)(301 K) = 0.0397 mol H2. Since the reaction is 1:1, moles of NaH = moles of H2 = 0.0397 mol. The molar mass of NaH is 24.0 g/mol, so mass = 0.0397 mol × 24.0 g/mol = 0.9528 g, which rounds to 0.925 g.

Sodium Hydride Reacts with Excess Water to Produce Aqueous Sodium