A 0.2500 g sample of an alloy reacts with to form hydrogen gas: 2Al(s) + 6H+(aq) 2Al3+(aq) + 3H2(g) Zn(s) + 2H+(aq) Zn2+(aq) + H2(g) The hydrogen produced has a volume of 0.147 L at 25ºC and 755 mm Hg. What is the percentage of zinc in the alloy

The mass percent of zinc in the alloy is 78.68 %

Explanation:

We are given:

Mass of sample of alloy = 0.2500 g

Let the mass of aluminium be 'x' grams and mass of zinc will be (0.2500 - x)  g

To calculate the amount of hydrogen gas produced, we use the equation given by ideal gas which follows:

where,

P = pressure of the gas = 755 mmHg  

V = Volume of the gas = 0.147 L

T = Temperature of the gas =

R = Gas constant =

n = number of moles of hydrogen gas = ?

Putting values in above equation, we get:

To calculate the number of moles, we use the equation:

   .....(1)

Molar mass of aluminium = 27 g/mol

Putting values in equation 1, we get:

The chemical equation follows:

By Stoichiometry of the reaction:

2 moles of aluminium produces 3 moles of hydrogen gas

So, moles of aluminium will produce = of hydrogen gas

Molar mass of zinc = 65.4 g/mol

Putting values in equation 1, we get:

The chemical equation follows:

By Stoichiometry of the reaction:

1 mole of zinc produces 1 moles of hydrogen gas

So, moles of zinc will produce = of hydrogen gas

To calculate the mass percentage of zinc in alloy, we use the equation:

Mass of zinc = (0.2500 - x) = [0.2500 - 0.0533] = 0.1967 g

Mass of alloy = 0.2500 g

Putting values in above equation, we get:

Hence, the mass percent of zinc in the alloy is 78.68 %