Final answer:
To convert 74.2 cm of Hg to atmospheres, you can use the equation (74.2 cm of Hg) × (1 atm / 760 mm of Hg) × (136 / 1) = 0.1 atm.
Step-by-step explanation:
In a mercury barometer, a value of 74.2 cm of Hg was obtained. To convert this measurement to atmospheres, we need to understand that atmospheric pressure at sea level is approximately 760 mm of Hg or 1 atm.
Since the density of mercury is 13.6 times greater than water, a mercury barometer only needs to be about 136 times shorter than a water barometer to measure atmospheric pressure. Therefore, 74.2 cm of Hg is equivalent to:
74.2 cm of Hg × (1 atm / 760 mm of Hg) × (136 / 1) = 0.1 atm
So, 74.2 cm of Hg is equal to 0.1 atmospheres.