8. A volume of 7.5 L of hydrogen gas at STP was produced from the single-replacement

reaction of zinc with nitric acid. Calculate the mass of zinc needed for this reaction.

20.60 g

Explanation:

We are given;

Volume of hydrogen gas produced at STP as 7.5 L

Required to determine the mass of zinc needed for the reaction.

We are going to first write the equation for the reaction;

Zn (s) + 2HNO₃ (aq) → Zn (NOₐ) ₂ + H₂ (g)

Now, we determine the number of moles of Hydrogen gas.

we know that 1 mole of a gas occupies 22.4 L at STP

Therefore;

Moles of Hydrogen = 7.05 L : 22.4 L/mol

= 0.315 moles

Then, we determine the number of moles of Zinc that reacted

From the reaction 1 mole of zinc reacts to produce 1 mole of hydrogen.

Therefore,

Moles of Zinc = Moles of Hydrogen

Thus, moles of zinc = 0.315 moles But, molar mass of zinc is 65.38 g/mol

Hence;

Mass of Zinc = 0.315 moles * 65.38 g/mol

= 20.60 g

Thus, the mass of zinc that reacted 20.60 g