How many molecules of hydrogen gas are present in a 750 ml
container at STP?

1.99 x 10²² molecules H2

Explanation:First we will solve for the moles of H2 using Ideal gas law PV= nRT then derive for moles ( n ).

At STP, pressure is equal to 1 atm and Temperature is 273 K.

Convert volume in mL to L:

750 mL x 1 L / 1000 mL

= 0.75 mL

n = PV/ RT

= 1 atm ( 0.75 L ) / 0.0821 L.atm/ mole.K ( 273 K)

= 3.3x10-² moles H2

Convert moles of H2 to atoms using Avogadro's Number.

3.3x10-² moles H2/ 6.022x10²³ atoms H2 / 1 mole H2

= 1.99x10²² atoms H2