Based on the lab conditions below, determine the answer to all questions highlig
ID: 85921 • Letter: B
Question
Based on the lab conditions below, determine the answer to all questions highlighted in yellow.
To investigate the difference between hydrophilic and hydrophobic substances, let's investigate that old adage that "oil and water don't mix". Start by pouring a small amount of tap water into the bottom of a tall glass container (suitable for swirling) to create a layer large enough for you to see clearly (I would recommend at least 1 inch deep). Then, pour in just enough cooking oil to create another layer that at least stretches all the way across the glass: notice that this layer forms on TOP of the water layer. {Why?} Next, swirl the glass to mix the oil and water as thoroughly as possible. {What do you see now?} Let the glass sit undisturbed long enough for the layers to separate again. {Why don't they stay together?} Take a SIDE-VIEW picture of your water-and-oil when they are completely separated. Optional, but cool: now, add 3-4 drops of food coloring. {Where does the food coloring go?} Swirl the glass again to thoroughly mix the layers together and distribute the food coloring as completely as possible. {Where is the food coloring now? Based on what you see, is food coloring hydrophobic or hydrophilic?} If you don't have food coloring, but want to see a similar effect (or do both!), add some table salt to the container and see where the salt goes. Finally (not optional!), add about the same amount of dish soap to your mixture as there is oil in it. Swirl to mix thoroughly. {What is different now, with the soap added to the mix, versus the water-and-oil only situation?} Take a SIDE-VIEW picture of your soap, water, and oil mixture when it is mixed. Soaps and detergents are unique molecules, with the property of being amphipathic, which means they are hydrophobic at one end, and hydrophilic at the other... so they can form a link between water and oil that allows us to do things like wash anything oily off our dishes, and ourselves! You should be able to dump this down your kitchen drain now, but run some hot water as you do it, to be sure you don't create a clog with the oil.Explanation / Answer
Oil is less dense than water and hence it doesn't mix but forms a layer on top of water. The cohesive forces between the water molecules or between the oil molecules are more than the adhesive forces between oil and water and hence they separate out.
On mixing the oil and water layers which are stable become unstable and you can see individual broken down globules floating around. When left undisturbed the layers reform. They do not stay mixed because of the density difference and the cohesive forces.
Food coloring is hydrophilic or water loving and hence is immisible in oil and stays undissolved in the oil layer and with time eventually moves down into the water layer
If it is shaken, the drops move down into the water portion
On adding detergent, the oil and water layers mix. Detergents have a polar hydrophilic head which interacts with the water layer and a long hydrophobic tail which interacts with the oil layer and hence mixing can occur forming an emulsion.
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