A container is filled with 0.25 liter of water and 0.75 liter of oil. At first the oil and water appear to mix, but after 10 minutes the oil and water separate as shown. This separation occurs because the
oil -
A. has a greater volume than the water
B. has a greater mass than the water
C. is less soluble than the water
D. is less dense than the water
Hey

Explanation:

Water molecules are polar molecules. That means one end of the molecule has a positive charge and the other end has a negative charge. This allows water molecules to bond together. Oil molecules, on the other hand, are non-polar.

Have you ever dissolved salt in water? How about sugar or coffee grounds? These things mix easily with water because they also have polar molecules. They’re able to bond with the water molecules.

However, non-polar molecules only mix well with other non-polar molecules. This explains why oil doesn’t mix well with water. Their molecules aren’t able to bond.

So what happens when you try to mix oil and water? The water molecules attract each other, and the oil molecules stick together. That causes oil and water to form two separate layers. Water molecules pack closer together, so they sink to the bottom, leaving oil sitting on top of the water.

Have you ever shaken a bottle that contained both oil and water? If so, you know that the two did mix for a short time. That’s because you caused emulsion. You forced the liquids to mix with each other. However, that mixing doesn’t last long! If you look at the bottle again after a minute or so, you’ll see that the water and oil have separated once again.

You can get oil and water to mix together for longer periods. You just have to add an emulsifier. That’s a molecule with one end that has one polar end and one non-polar end. Egg yolks are common emulsifiers. So is soap! It attracts oil on one end and water on the other. That’s what it does when it cleans your hands!

The next time you’re in a restaurant, look for a container of oil and vinegar dressing sitting on the table. Is all the oil at the top? That’s because the vinegar is mixed with water. Give it a good shake and watch what happens!

synovial joints are characterized by the presence of a joint cavity. the walls of this space are formed by the articular capsule, a fibrous connective tissue structure that is attached to each bone just outside the area of the bone’s articulating surface. the bones of the joint articulate with each other within the joint cavity.

friction between the bones at a synovial joint is prevented by the presence of the articular cartilage, a thin layer of hyaline cartilage that covers the entire articulating surface of each bone. however, unlike at a cartilaginous joint, the articular cartilages of each bone are not continuous with each other. instead, the articular cartilage acts like a teflon® coating over the bone surface, allowing the articulating bones to move smoothly against each other without damaging the underlying bone tissue. lining the inner surface of the articular capsule is a thin synovial membrane. the cells of this membrane secrete synovial fluid (synovia = “a thick fluid”), a thick, slimy fluid that provides lubrication to further reduce friction between the bones of the joint. this fluid also provides nourishment to the articular cartilage, which does not contain blood vessels. the ability of the bones to move smoothly against each other within the joint cavity, and the freedom of joint movement this provides, means that each synovial joint is functionally classified as a diarthrosis.

outside of their articulating surfaces, the bones are connected together by ligaments, which are strong bands of fibrous connective tissue. these strengthen and support the joint by anchoring the bones together and preventing their separation. ligaments allow for normal movements at a joint, but limit the range of these motions, thus preventing excessive or abnormal joint movements. ligaments are classified based on their relationship to the fibrous articular capsule. an extrinsic ligament is located outside of the articular capsule, an intrinsic ligament is fused to or incorporated into the wall of the articular capsule, and an intracapsular ligament is located inside of the articular capsule.

at many synovial joints, additional support is provided by the muscles and their tendons that act across the joint. a tendon is the dense connective tissue structure that attaches a muscle to bone. as forces acting on a joint increase, the body will automatically increase the overall strength of contraction of the muscles crossing that joint, thus allowing the muscle and its tendon to serve as a “dynamic ligament” to resist forces and support the joint. this type of indirect support by muscles is very important at the shoulder joint, for example, where the ligaments are relatively weak.

additional structures associated with synovial joints

a few synovial joints of the body have a fibrocartilage structure located between the articulating bones. this is called an articular disc, which is generally small and oval-shaped, or a meniscus, which is larger and c-shaped. these structures can serve several functions, depending on the specific joint. in some places, an articular disc may act to strongly unite the bones of the joint to each other. examples of this include the articular discs found at the sternoclavicular joint or between the distal ends of the radius and ulna bones. at other synovial joints, the disc can provide shock absorption and cushioning between the bones, which is the function of each meniscus within the knee joint. finally, an articular disc can serve to smooth the movements between the articulating bones, as seen at the temporomandibular joint. some synovial joints also have a fat pad, which can serve as a cushion between the bones.

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