Part A itm 22 , Binary compounds of alkali metals and hydrogen react with water

Question

Part A

itm 22 , Binary compounds of alkali metals and hydrogen react with water to liberate hydrogen gas. The hydrogen gas from the reaction of a sample of sodium hydride with an excess of water fills a volume of 0.500 L above the water. The temperature of the gas is 35 C and the total pressure is 765 mmHg .

a) Find the mass of hydrogen gas liberated.

b) Find the mass of sodium hydryide that reacted.

Part B

Itm 21 ,

a) The decomposition of 4.41 atm of HCl undergoes a decomposition by the following reaction:

2HCl(g)H2(g)+Cl2(g)

Determine the partial pressure of H2. (Assume 100% decomposition)

b) Determine the partial pressure of Cl2. (Assume 100% decomposition)

c) If this reaction were to take place, what would the total pressure of the system be upon complete decomposition of HCl.

Explanation / Answer

Part A.

a) PV = nRT

n = PV/RT

we have,

n = moles = ?

P = 765 mmHg = 1.00658 atm

V = 0.5 L

T = 35 oC = 35 + 273 = 308 K

R = 0.08205 L.atm/K.mol

Feed values,

n = 1.00658 x 0.5/0.08205 x 308

   = 0.02 mols

moles = g/molar mass

mass of H2 gas liberated = 0.02 x 2.06 = 0.0412 g

b) 2 moles of NaH gives off 1 mole of H2 gas

mass of sodium hydride reacted = (0.02/2) x 24 = 0.24 g

Part B.

a) 2 moles of HCl gives 1 mole of H2

So, 4.41 atm HCl would give = 2.205 atm of H2 gas

b) 2 moles of HCl gives off 1 mole of Cl2

partial pressure of Cl2 = 2.205 atm

c) Total pressure of the system after complete decomposition of HCl would be,

Pressure = 4.41 atm

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