CHEMISTRY SEPTEMBER 22, 2014 Lab 01 – Safety Inspection

SCIENCE STARTER You have 3 minutes Work silently and individually

OBJECTIVE SWBAT give evidence of cohesion and surface tension in a liquid.

AGENDA – Science Starter – Demonstration – Review of concept of surface tension and cohesion

REMINDER LAB SAFETY AWARENESS POSTER

DEMONSTRATION CAN YOU CENTER ME?

COHESION Water molecules are attracted to other water molecules. The oxygen end of water has a negative charge and the hydrogen end has a positive charge. The hydrogens of one water molecule are attracted to the oxygen from other water molecules. This attractive force is what gives water its cohesive properties.

SURFACE TENSION Surface tension is the name we give to the cohesion of water molecules at the surface of a body of water. The cohesion of water molecules forms a surface “film” or “skin.” Some substances may reduce the cohesive force of water, which will reduce the strength of the surface “skin” of the water.

DEMONSTRATION Magic of an inverse glass of water

ADHESION Water molecules are cohesive to other surfaces. When the cohesive forces between the liquid molecules are greater than the adhesive forces between the liquid and the walls of the container, the surface of the liquid is convex ( ∩). When the cohesive force between the liquid molecules are less than the adhesive forces between the liquid and the walls of the container, the surface of the liquid is concave.

ADHESION VS COHESION

AIR PRESSURE There is a pressure difference between the room and the inside of the glass bottle. This difference cause a net force upward that cancel out the weight of the water.

CAPILLARY ACTION Capillary action is the result of cohesive and adhesive forces. When a liquid flows through a narrow space, the cohesive and adhesive forces act together to lift it against the natural force of gravity.

EXPLORE Given: – An empty container – A container of water – Rolled up paper napkin with one end in the container of water and the other end in the empty container. – Predict what you think will happen and why.