Question

A sample of air is collected in the morning at an ambient temperature of 25°C. The concentration of carbon monoxide (CO) in this sample is 30 ppmv (ppm by volume). The same sample is analysed later in the afternoon when the sample temperature is 35°C. The analysis results will show the CO concentration as _______.

• A. < 29 ppmv
• B. > 30 ppmv
• C. = 30 ppmv
• D. 29 ppmv

Hint:

When measuring gas concentrations, the value in ppmv typically remains constant if the volume of the gas is measured at the same standard conditions, despite temperature variations.

Answer 1

The Correct Option is C

The concentration of gases like carbon monoxide (CO) is typically expressed in parts per million by volume (ppmv). The concentration in ppmv is generally independent of the temperature, provided the sample is measured in the same way.
However, if the temperature changes, the volume of the gas can change according to the ideal gas law. This change in volume would lead to a change in the concentration if measured by volume. Since the question asks for the concentration at a different temperature (from 25°C to 35°C), we need to understand that the concentration by volume, given the same number of CO molecules, remains constant.
Thus, the correct answer is that the concentration of CO remains the same at 30 ppmv despite the temperature change.
Final Answer: \[ \boxed{30 \, \text{ppmv}}. \]