I need help finding the unknown metal.

Question

Suppose you react 0.06916g of an unknown that forms one mole of hydrogen gas for each mole of metal. If you collect 38.98 mL of dry hydrogen at 298 K and P_atm = 689 torr, calculate the molar mass of the metal. If the unknown may be any metal in the periodic table, what is the identity of your unknown?

Answer 1

Let M = unknown metal

one mole M generates one mole H₂

We can find the moles of H₂ gas generated by using the ideal gas law PV = nRT and solve for n (moles)

n = PV/RT = (698 torr)(0.03898 L)/(62.36 L*torr/K*mol)(298K) = 0.001464 moles H₂ gas

Since 1 mole H₂ gas comes from 1 mole of metal (M), we know we must have 0.001464 moles of M

Molar mass = g/mole = 0.06916 / 0.001464 moles = 47.2 g/mole

The closest match in the periodic table would be titanium (atomic mass 47.9), but titanium doesn't react to produce hydrogen gas. The closest metal that does react with acid to produce H₂ gas would be calcium (atomic mass 40.08).