Investigating the Properties of Water

Investigating the Properties of Water Part 1: How much water will a coin hold? After conducting the experiment, it was concluded that a clean, dry 10-cent coin could hold 28 drops of water. However, when a thin layer of dish soap was added onto the coin’s surface, it was discovered that the coin could only hold 10 drops of water before overflowing. In both cases, when the face of the coin is fully covered in water, the droplets begin to build upwards, forming a dome shape. This occurrence can be explained by cohesion and surface tension. Water molecules possess two positively charged hydrogen atoms and one negatively charged oxygen atom, thus producing an unusually strong cohesion with one another. This type of intermolecular force is known as hydrogen bonding, and, when imbalanced, forms surface tension. In order to remain balanced, the water molecules must exert forces in all directions on other molecules. However, since the molecules at the top cannot exert a force upwards as there are no molecules above them, these molecules become imbalanced. When imbalanced, the molecules pull inwards. This creates surface tension, and it results in a decrease in surface area. Eventually, though, the gravity on the water molecules will overtake these hydrogen bonds and the dome of water will burst. The act of breaking surface tension can also be done with surfactants. Surfactants are compounds that weaken the surface tension of liquids. They obstruct cohesive forces, including hydrogen bonds, and decrease surface tension with ease. When dish soap was applied to the coin, the water molecules were interrupted by the surfactant, resulting in a quicker break of surface tension. Condition of coin Amount of water droplets before overflow Dry, clean dime 28 drops Dime with soap 10 drops Fig. 1: Coin with no soap at 27 drops Part 2: Water Drop Shapes When placing droplets of water on a ceramic plate and wax paper, it was observed that the droplet was flat and spread out, whilst the droplet on wax paper formed a dome shape. The difference in these drop shapes was due to adhesion, cohesion, and hydrophobic interactions. Water molecules are highly cohesive, meaning they tend to attract one another. Additionally, wax is nonpolar and hydrophobic, so when the water droplet was placed on the wax paper, the water molecules were not attracted to the wax but rather to each other. The hydrophobic interaction between the water and wax molecules allowed for an increase in surface tension and decrease in surface area. The ideal shape for minimal surface area is a sphere, but gravity upon the molecules makes a perfect sphere impossible, thus a dome shape is formed. This cannot occur on ceramic plates, however, because the water molecules are able to adhere to the plate a lot better. The adhesion between the two disrupts the water droplet’s surface tension and causes it to flatten. Fig. 2: Water drop on ceramic plate Fig. 3: Water drop on wax paper Part 3: The Climbing Properties of Water When the coffee filter was placed inside the barely-filled glass, the water started to move up the coffee filter immediately. By 5 minutes, the water-soluble ink had already gone half way up the filter, and after 15 minutes, the ink reached its way up to the top of the coffee filter. This effect can be explained by capillary action and adhesion. The ink used was water-soluble, meaning that it has polar molecules that could form hydrogen bonds with the water molecules easily. The ink, coupled with the coffee filter, allowed for the water molecules to engage in adhesion more than cohesion (when the water molecules link with each other), resulting in capillary action. As the water was carried up the coffee filter because of capillary action, the ink went along and faded as the molecules continued to spread out with the water molecules. Fig. 4: Filter after 2 minutes Fig. 5: Filter after 15 minutes Time of coffee filter in water Ink measurements on coffee filter 2 minutes 1.7 cm 5 minutes 3.2 cm 10 minutes 5.4 cm 15 minutes 6.0 cm Part 4: Can Water Float? When ice cubes were placed into 2 cm of water and 2 cm of rubbing alcohol, it was discovered that the ice cube in water floats whilst the ice cube in rubbing alcohol sinks. This occurs because ice becomes less dense than water when frozen. When water is frozen, the molecules expand, but since water is polar, it allows for the hydrogen bonds to hold onto the molecules. The spacing between these molecules makes it less dense than water. However, even with this lessened density, it is still denser than alcohol, therefore it sinks when placed in rubbing alcohol. Fig. 6: Ice in water Fig. 7: Ice in rubbing alcohol Part 5: Solubility This experiment revealed that ¼ cup of water could dissolve 9 teaspoons of sugar, while ¼ cup of vegetable oil could not dissolve any teaspoons of sugar. The sugar was able to dissolve in water because of hydrogen bonding and intermolecular forces of attraction. Sugar molecules, also known as sucrose molecules, consist of 12 carbon atoms, 22 hydrogen atoms, and 11 oxygen atoms. These atoms are held together by covalent bonds, and the molecules connect with each other by way of glycosidic bonds. When the sugar is stirred in water, the water molecules (H 2O) form a type of intermolecular force called hydrogen bonds with the sucrose molecules, and the glycosidic bonds are disrupted. Since water molecules and sucrose molecules are both polar, they attract to each other with ease. Nonetheless, covalent bonds are stronger than hydrogen bonds, so the carbon, hydrogen, and oxygen atoms within each sucrose molecule stay connected. Eventually, the water becomes a saturated solution; all the water molecules have taken a sucrose molecule, thus leaving the excess sugar molecules undissolved. Whilst water can take in large amounts of sugar, oil is quite the opposite because oil molecules are nonpolar and hydrophobic. This means that these molecules do not attract or attach to polar molecules such as water and sucrose. When hydrophobic molecules interact - or rather lack an interaction - with water molecules, it can be described as a hydrophobic interaction. Solvent Number of tablespoons of sugar dissolved Water 9 Vegetable oil 0