Question

The maximum size the balloon can get before popping (or flying off the flask) is 6.00 L at 1.00 atm of pressure and a temperature of 45°C. What maximum concentration of hydrochloric acid can be used (to just keep the balloon from popping) if 65.0 mL of HCl is added to 9.00 g of magnesium?

Answer 1

Answer:

The maximum concentration of HCl that can be used is 7.08 M

Explanation:

The reaction that takes place is:

• 2HCl(aq) + Mg → MgCl₂ + H₂

The available moles of Mg are:

• 9.00 g Mg ÷ 24.3 g/mol = 0.370 mol

H₂ gas is produced and fills the balloon. We use PV=nRT to calculate the maximum moles of H₂ that can be produced before the balloon pops off:

• 1.00 atm * 6.00 L = n * 0.082 atm·L·mol⁻¹·K⁻¹ * 318.16 K

• n = 0.230 mol H₂

Now that we know that we have more than enough moles of Mg to produce 0.230 moles of H₂, we know that HCl is the limiting reactant.

We calculate the required moles of HCl:

• 0.230 mol H₂ * $\frac{2molHCl}{1molH_{2}}$ = 0.460 mol HCl

Now we use C = n/V to calculate the concentration of HCl:

• C = 0.460 mol HCl / 0.065 L = 7.08 M