A flask containing 12 g of a gas of relative molecular mass 120 at a pressure of 100 atm was evacuated by means of a pump until the pressure was 0.01 atm. Which of the following is the best estimate of the number of molecules left in the flask ( N 0=6 × 1023 mol -1) ?

Question

A flask containing 12 g of a gas of relative molecular mass 120 at a pressure of 100 atm was evacuated by means of a pump until the pressure was 0.01 atm. Which of the following is the best estimate of the number of molecules left in the flask ( N 0=6 × 1023 mol -1) ? (A) 6 × 1019 (B) 6 × 1018 (C) 6 × 1017 (D) 6 × 1013

Tardigrade Admin · Accepted Answer

P1 V1=n1 R T1 P2 V2=n2 R T2 (n2/n1)=(P2/P1) n2=0.1 × (0.01/100)=10-5 mol =6 × 1018 molecules

$6 \times 1 0^{19}$

$6 \times 1 0^{18}$

$6 \times 1 0^{17}$

$6 \times 1 0^{13}$

$P_{1} V_{1} = n_{1} R T_{1}$
$P_{2} V_{2} = n_{2} R T_{2}$
$\frac{n _{2}}{n _{1}} = \frac{P _{2}}{P _{1}}$
$n_{2} = 0.1 \times \frac{0.01}{100} = 1 0^{- 5} m o l$
$= 6 \times 1 0^{18}$ molecules

Q. A flask containing 12g of a gas of relative molecular mass 120 at a pressure of 100atm was evacuated by means of a pump until the pressure was 0.01atm. Which of the following is the best estimate of the number of molecules left in the flask (N0​=6×1023mol−1) ?

6×1019

6×1018

6×1017

6×1013

P1​V1​=n1​RT1​ P2​V2​=n2​RT2​ n1​n2​​=P1​P2​​ n2​=0.1×1000.01​=10−5mol =6×1018 molecules

$6 \times 1 0^{19}$

$6 \times 1 0^{18}$

$6 \times 1 0^{17}$

$6 \times 1 0^{13}$

$P_{1} V_{1} = n_{1} R T_{1}$
$P_{2} V_{2} = n_{2} R T_{2}$
$\frac{n _{2}}{n _{1}} = \frac{P _{2}}{P _{1}}$
$n_{2} = 0.1 \times \frac{0.01}{100} = 1 0^{- 5} m o l$
$= 6 \times 1 0^{18}$ molecules