Chemistry Gases MDCAT 2012
PMDC Verified Question 63 of 65
The number of molecules in 22.4 \( \text{dm}^3 \) of \( \text{H}_2 \) gas at 0°C and 1 atm are:
A
\( 6.02 \times 10^{24} \)
B
\( 6.02 \times 10^{25} \)
C
\( 6.02 \times 10^{23} \)
D
\( 6.02 \times 10^{22} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: \( 6.02 \times 10^{23} \)
Concept:

Standard Temperature and Pressure (STP) conditions are defined as 0??C (273.15 K) and 1 atm. At STP, 1 mole of any ideal gas occupies exactly 22.414 \( ext{dm}^3 \).

Solution:

  • The given volume is 22.4 \( ext{dm}^3 \) at STP, which corresponds to exactly 1 mole of \( ext{H}_2 \) gas.
  • According to Avogadro's concept, 1 mole of any substance contains Avogadro's number of entities (molecules).
  • Therefore, the number of molecules = \( 1 ext{ mole} imes (6.02 imes 10^{23} ext{ molecules/mole}) = 6.02 imes 10^{23} \).


Why other options are incorrect:

  • Options A, B & D: These represent incorrect orders of magnitude (\(10^{24}, 10^{25}, 10^{22}\)) rather than the standard Avogadro constant (\(6.02 imes 10^{23}\)).

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