Question

Number of molecules and moles in 2.8375 litre of O₂ at STP.

Answer 1

Number of moles = 0.1266 moles 
Number of molecules = 0.7625 × 10²³

Answer 2

At STP (Standard Temperature and Pressure), the temperature is 273.15 K and the pressure is 1 atm.
The molar volume of any ideal gas at STP is 22.4 \(\frac{L}{mol}\). 
Therefore, we can use the following formula to calculate the number of moles of O₂ :
⇒ n = \(\frac{V}{V_M}\) , 
where n is the number of moles, 
V is the volume of the gas (2.8375 L)
\(V_M \)is the molar volume of the gas at STP (22.4 \(\frac{L}{mol}\)).
n = \(\frac{2.8375}{22.4}\) \(\frac{L}{mol}\)
n = 0.1266 mol
We can use the Avogadro's number (6.022 x \(10^{23}\)) to calculate the number of molecules:
Number of molecules = n x \(N_A\)
where N_A is Avogadro's number.
Number of molecules = 0.1266 mol x 6.022 x 10²³\(\frac{L}{mol}\)
Number of molecules = 7.614 x 10²² molecules
Therefore, there are 0.1266 moles and 7.614 x 10²² molecules of O₂ in 2.8375 L of \(O_2\) at STP.
Number of moles = 0.1266 moles 
Number of molecules = 0.7625 × 10²³