(solved)Question 1.13 of NCERT Class XI Chemistry Chapter 1

Question 1.13
NCERT Class XI Chemistry

Pressure is determined as force per unit area of the surface. The SI unit of pressure, pascal is as shown below: 1Pa = 1N m-2. If mass of air at sea level is 1034 g cm-2, calculate the pressure in pascal.

Solution in Brief
(detailed solution given after the video below)

mass of air column is given as 1034 grams per sq. cm, or 10340 kg per sq.m. The gravitational force on this air column is (10340 x 9.8) N per sq.m = 101332 N per sq. m = 1.0 x 10^5 Pa. The result is rounded off to 2 decimal places because 9.8 is least precise with 2 SF.

Answer is 101332 Pa, or in 2 SF: 1.0 x 10^5 Pa.

Video Explanation
(detailed solution given after this video)

Please watch this youtube video for a quick explanation of the solution:

Solution in Detail

$ \begin{aligned} &\text{mass of air } = \frac{1034 \text{ grams}}{\text{cm}^2}\\\\ & = \frac{1034 \times 10^{-3}\text{ kg}}{(10^{-2}\text{ m})^2}\\\\ & = 10340 \text{ kg m}^{-2}\\\\ &\text{pressure is due to gravitational weight}\\\\ &\therefore \text{Pressure } = 10340 \times g \text{ N m}^{-2}\\ &\text{take g} = 9.8 \text{ ms}^{-2}\\ &\therefore \text{Pressure } = 10340 \times 9.8 \text{ N m}^{-2}\\\\ &\text{SF in } 10340 \text{ are } 5 \text{ and SF in } 9.8 \text{ are 2}\\ &\therefore \text{SF in product will be } 2\\\\ &\therefore \text{Pressure } = 101332 \text{ N m}^{-2}\\ &= 1.0 \times 10^5 \text{ Pa (SF are 2)}\:\underline{Ans} \end{aligned} $