The Disappearing Liquid Grade Level: 2 Strand: Earth and Space Systems Topic: Air and Water in the Environment Specific Expectations: General: •
demonstrate an awareness of the forms in which water and air are present in the environment, and describe ways in which living things are affected by water and air Specific: • recognize that water exists in three states on earth (e.g., solid – visible as ice; liquid ‐ visible as rain or as water in lakes, streams, etc.; gas – present but invisible as water vapour); • identify the factors that cause things to dry quickly or slowly (e.g., air temperature; amount of moisture in the air; amount of wind); • recognize evidence of the water cycle (e.g., observe water in a closed container and water in an open container; observe puddles evaporating after a rainstorm) Materials Needed: •
•
•
•
rubbing alcohol plastic cups eye droppers use of each students hand Procedure: •
•
•
Have each student hold up one of their hands with the back of the hand facing upwards in a horizontal state Have each student take the eye dropper with one hand and drop some of colourless liquid on to the back of their other hand, or they can use a cotton ball to rub on if eyedroppers are not available Have students observe and hypothesize about what is happening Scientific Explanation: When a liquid such as alcohol disappears, it is being transformed into its vapour state (gas). This process is known as evaporation and it occurs when liquid molecules gain enough energy to escape the surface of the liquid layer. Alcohol in its liquid state is volatile or in a state in which it is highly changeable and therefore can evaporate quickly. Thus, alcohol drops placed on the back of the hand are able to evaporate within a few seconds to a minute. In order for this evaporation to occur and a liquid to change into a vapor (gas) energy is required, and in this case that energy comes in the form of heat. Therefore, the alcohol is heated with the body temperature of the hand. However, if heat is not available to a liquid, it will then withdraw heat from its surrounding environment. Similarly, when the drop of alcohol is placed on the hand it spreads out to gain more surface area which also increases its evaporation rate. In addition to temperature in the form of heat and surface area, wind can also increase the evaporation rate of any liquid. In conclusion, the alcohol molecules become highly energized by the temperature of the body and its increased surface area (expands in area when dropped on hand) thereby giving the molecules enough energy to escape the surface layer of liquid and become a vapor (gas). References: http://www.edu.gov.on.ca/eng/curriculum/elementary/scientec18curr.pdf http://tiger.coe.missouri.edu/~pgermann/DiscEvent/Heat_Transfer/Evaporation/evaporation.h
tml http://www.k12science.org/curriculum/drainproj/evaporation.html http://www.wikipedia.org/ Opportunities and other consideration: •
Real Life applications ƒ Can relate this activity to perspiration. You can explain that when a person engages in physical activity such as running, there is a buildup of energy. This buildup of energy causes the person to become hot and they perspire which then causes the liquid to vapourize, which releases heat and cools the person down. However, on a humid day the air is saturated with vapour molecules so when you sweat or perspire it is unlikely that it will evaporate causing you to feel hotter. ƒ You can tell children to go home and get their parents to boil water in a kettle and they can observe the vapour when it starts to boil. Glossary: Liquid: is one of the four principle states of matter. A liquid is a fluid that can freely form a distinct surface at the boundaries of its bulk material. Vapour: is the gas phase component of another state of matter (e.g. liquid or solid) which does not completely fill its container. When a liquid has completely evaporated it is said that the system has been completely transformed to the gas phase. Gas: is one of the four major states of matter, consisting of freely moving atoms or molecules without a definite shape. Volatile: means something changing or changeable. Evaporation: is the process of water molecules gaining enough energy to escape the surface of the water layer. Names of Presenters: Ashley Schneider and Carolyn Iacino Section 4