Final answer:
CO₂ is collected in a gas jar by upward displacement of water due to its lower density and low solubility in water. The water displacement technique is utilized, and Dalton's Law helps to ensure that the measured gas pressure is accurate, accounting for atmospheric pressure and water vapor pressure.
Step-by-step explanation:
CO₂ is collected in a gas jar by upward displacement of water because it is less dense than water and does not dissolve significantly in water. This method is known as the water displacement technique. When CO₂ gas is produced during a chemical reaction in a reaction flask, it travels through rubber tubing and into an inverted bottle filled with water. As CO₂ enters the bottle, it displaces the water because of its lower density, causing the water to move downwards and allowing the gas to accumulate at the top of the bottle. This process continues until the water is fully displaced and the bottle is filled with CO₂. The collected gas volume can be measured and, using the concept of Dalton's Law, the pressure of the collected gas can be equated to atmospheric pressure, which is measurable with a barometer. Additionally, the vapor pressure of water must be considered to get the true pressure of the gas.