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Why the surface of water in a measuring cylinderis curved? That is called a meniscus. It comes from the Greek word for “crescent”. It is a curve in the surface of a molecular substance and is produced in response to the surface of the container or another object. It can be either concave or convex. A convex meniscus occurs when the molecules have a stronger attraction to each other than to the container. This may be seen between mercury and glass in barometers. A concave meniscus occurs when the molecules of the liquid attract those of the container. This can be seen between water and an unfilled glass. Capillary action acts on concave menisci to pull the liquid up, increasing the amount of energetically favorable contact area between liquid and container. Adhesion between the liquid and the container ﻿encourages as much liquid as possible to be in contact with the container. Some containers may attract water molecules much less. Many kinds of plastics, called "hydrophobic", (e.g. teflon) have very small adhesive forces with water, and if you make a container out of these you will get a convex meniscus with water, too. Mercury has very small adhesive forces with most container materials, and strong cohesive forces. Little drops of mercury will form into almost spheres when spilled on most surfaces (gravity will bend them out of shape). While water and other liquids is made up of electrically polar molecules. How to read a meniscus correctly? Measure the meniscus at eye level from the center of the meniscus. In the case of water and most liquids, the meniscus is concave. Mercury produces a convex meniscus.

**ACE 2** __** Differences between evaporation and boiling **__ -Evaporation happens at any temperature, boiling happens only at the boiling point. - Evaporation takes place only at the surface, boiling takes place throughout the liquid. - Boiling takes energy in to occur, while evaporation lets only the molecules with the highest kinetic energy out, leaving the rest of the water with lowest kinetic energy. - Boiling happens when heat is added from the bottom and evaporation is when heat is added from the top. For instance, when you boil water in a pot, it is being heated from the bottom, so air bubbles form at the bottom and rise through the liquid, to the top. It would be evaporation if the heat was added from the top (no bubbles would form). ~ __** How does it occur? **__ Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. Evaporation is a type of transition; it is the process by which molecules in a liquid state (e.g. water) spontaneously become gaseous (e.g. water vapour). Generally, evaporation can be seen by the gradual disappearance of a liquid from a substance when exposed to a significant volume of gas. With sufficient heat added from the top, the liquid would turn into vapour quickly. When the molecules collide, they transfer energy to each other in varying degrees, based on how they collide. Sometimes the transfer is so one-sided for a molecule near the surface that it ends up with enough energy to escape. Boiling is the rapid vaporization of a liquid which typically occurs when a liquid is heated to its boiling point. Boiling takes place throughout the liquid. Boiling takes in heat energy to occur. Boiling happens when heat is added from the bottom. ~ Thank you. Please click the link below to download the files.