Question

1. A mass of 135 g of an element is known to contain 3.01 × 1024 atoms. What is the element?

2. A young male adult takes in about 0.0005 m3 of fresh air during a normal breath. Fresh air contains approximately 21 % oxygen. Assuming that the pressure in the lungs is 9715 Pa, and air is an ideal gas at a temperature of 298 K, what is the number of oxygen molecules

Answer 1

1) m = 135 g

No. of atoms = 3.01 * 10^24

therefore, number of moles = no. of atoms present /Avogadro number

no. of moles = 3.01*10^24/(6.02*10^23)

no. of moles = 5 moles

therefore, 5 moles weigh 135 g

hence, weight of 1 mole = 135/5 = 27 g

Now, we know that Aluminium has a molecular mass of 27 g , therefore the element is ALUMINIUM

2) using ideal gas equation

PV = nRT

9715 * (21% of 0.0005) = n * 8.314 *298

n = 0.0004117 moles of oxygen

Therefore, number of oxygen molecules = 0.0004117 * 6.02 * 10^23

= 2.48 * 10^ 20 molecules of oxygen

Please ask your doubts or queries in the comment section below.

Please kindly upvote if you are satisfied with the solution.

Thank you.