How many nitrogen molecules are there in a 7 liter vessel filled with nitrogen with a density of 2 kg / m3?

We give the values from given in the SI system:
V = 7 l = 0.007 m³
1. Let’s write down the formula to determine the mass, through the specific gravity:
m = ρ * V
2. Determine the mass of nitrogen:
m = ρ * V = 2 * 0.007 = 0.014 kg.
3. Let’s write down an expression to determine the amount of a substance:
ν = m / M = N / Na, where m is the mass of the substance, M is the molar mass of the substance, N is the number of particles, Na is Avogadro’s constant Na = 6.023 * 10 ^ 23 1 / mol.
4. Let us express N from this expression:
N = m * Na / M
M (N2) = 2 * 0.014 = 0.028 kg / mol. (using the periodic table).
N = m * Na / M = 0.014 * 6.023 * 10 ^ 23 / 0.028 = 3.01 * 10 ^ 23.
Answer: there are 3.01 * 10 ^ 23 nitrogen molecules in the vessel.