PREDICTYou are at the beach and you just get out of the water. The sand starts to cover your feet. What does this sand feel like?

What does hydro mean? What does phobic mean?In cooking, where might a hydrophobic surface be used?

What is hydrophobic sand? What will happen when you mix hydrophobic sand with water?

Step 1:Feel the hydrophobic sand you are given. How does it differ in texture compared to sand you encounter at the beach?

Step 2: Pour some of the hydrophobic sand into the provided beaker filled with water. Make sure some sand sits on the top. What do you notice about the sand in the water? How is this different from the beach sand?

Observe

Step 3: Using the scoopula provided, push the scoopula vertically, about ½ inch, into the sand (which is sitting on the surface of the water). What happens to the scoopula? Does it feel wet or dry when taken out of the water?

Step 4: Stir the sand with the scoopula. What happens to the sand?

Step 5: Using your hand, reach into the water and touch the sand. Does it feel different then the sand that covers your feet at the beach?

ExplainUse the information you have gathered from your observations to explain what is happening.

The Chemistry:The term hydrophobic means “water fearing” and the term hydrophilic means “water loving”. Therefore, hydrophobic substances repel water, and hydrophilic substances absorb water. Water is made of oxygen and hydrogen atoms. Because of the size, structure, and covalent bonding of the oxygen and hydrogen atoms, water is a polar molecule. Regular sand is made up of covalent bonds of silicon and oxygen atoms (regular sand is not pure silica because it contains other mineral impurities). When you put regular sand into water, the partial positive and partial negative charges of the silica and water attract each other. Therefore, the sand absorbs the water. Magic Sand is made of pure silica and is coated with methyl (CH3) groups. These groups make Magic Sand a non–polar substance and a neutral molecule. Therefore, Magic Sand is not attracted to the partial charges of polar solvent water.

The Biology:Each grain of Magic Sand can be compared to a cell. A cell has a semi-permeable membrane, which allows molecules or ions, such as particles, electrolytes, and water to flow in and out of the cell (depending on the cell’s environment). Cells are suspended in interstitial fluid (similar to the grains of Magic Sand suspended in water). There is typically some fluid within the cells. The interstitial fluid moves in and out of the cells to maintain homeostasis (balance of density) within and outside the cell.