Question

12) 50.0 ml butane gas at STP contains how many molecules?​

Answer 1

We have to find the no of molecules in 50 ml of butane at STP.

solution : at Standard temperature and pressure,

T = 0°C = 273K

P = 1 atm

V = 50 ml = 0.05 litre [ given ]

Using formula, PV = nRT

Where n is no of moles of substance.

so, 1 × 0.05 = n × 0.082 × 273

⇒n = 0.05/(0.082 × 273) = 0.00223

Now no of molecules of butane = no of moles of butane × Avogadro's number

= 0.00223 × 6.023 × 10²³

= 0.01345 × 10²³

= 1.345 × 10²¹

Therefore the number of molecules of butane gas is 1.345 × 10²¹ (approx)