For every 1°C increase in temperature, the multiplying factor for pCO2 is:

• A. 7
• B. 3
• C. 1.5
• D. 0.5

Answer: (B)

pCO2 is very sensitive to temperature changes because the CO2-bicarbonate system and CO2 solubility in plasma shift as temperature rises. As temperature increases, CO2 becomes less soluble in the liquid phase, and the equilibria that keep dissolved CO2 in balance with the gaseous phase push pCO2 higher in order to maintain that balance. In many teaching resources, this practical correction is approximated by a multiplying factor of about 3 for each 1°C rise. That’s why the correct choice is the factor of 3 — it reflects a relatively strong temperature effect on pCO2 in this context.

The other options imply either an even larger or smaller effect or a reversal (pCO2 decreasing) with temperature, which does not align with how CO2 solubility and the carbonate system respond to warming in these calculations. Keep in mind this is a rough, context-specific rule of thumb used for instructional purposes, not an exact universal constant.