A convex meniscus occurs when the molecules have a stronger attraction to each other than to the container, as with mercury and glass. to hog silicon's electrons. Mercury produces a convex meniscus. The partially positive Water meniscus is convex, mercury menisucs is concave A concave meniscus, which is what you normally will see, occurs when the molecules of the liquid are attracted to those of the container. So, I fill the water right over here. Surface tensions of several liquids are presented in Table \(\PageIndex{2}\). Direct link to Ernest Zinck's post The mercury atoms are str, Posted 7 years ago. Direct link to SHIVANK VATSAL 's post At 6:52, how are MORE of , Posted 4 years ago. Meniscus. The tube experiences a downward force of magnitude 2r, where is the surface tension of the liquid. As you may have noticed, when water is in such a thin glass tube, it does not have a flat surface at the top. you spill some water, or you spill some milk. So why do, Posted 5 years ago. But once it came up, came in contact with the glass surface right The strong adhesive forces between the water and the glass, pull the sides of the water upwards along the glass forming a concave shaped meniscus. This, what I am circling and you stick it in the water, you will observe something very cool. The air pressure on the upper or concave side of the meniscus is the atmospheric pressure P. We know that the pressure on the convex side of the free surface is less than that on the concave side. are the glass molecules. Alternatively for mercury, the cohesive forces are stronger than the adhesive forces which allows the the meniscus to bend away from the walls of the capillary tube. Conversely, a convex meniscus occurs when the particles in the liquid have a stronger attraction to each other than to the material of the container. Cohesive forces between like molecules are responsible for a liquids viscosity (resistance to flow) and surface tension (elasticity of a liquid surface). we call capillary action. The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. For a flat meniscus, make sure the liquid is level. When mercury is placed in a graduated cylinder, the cohesive forces in the mercury are stronger than the adhesive forces between the mercury and the glass. For a convex meniscus, this is the uppermost or top point of the liquid. When liquid water is confined in a tube, its surface (meniscus) has a concave shape because water wets the surface and creeps up the side. Science Photo Library (SPL) To say, "Hey this is a meniscus." Capillary action is the basis for thin layer chromatography, a laboratory technique commonly used to separate small quantities of mixtures. Measure the meniscus at eye level from the center of the meniscus. Helmenstine, Anne Marie, Ph.D. "How to Read a Meniscus in Chemistry." So this is the glass right over here. So this right over here, that over there, that is co-, that is cohesion. (In other words, Water meniscus is convex, mercury menisucs is concave A meniscus can go up or down. And I would say, "Yes, In contrast, water exhibits a concave meniscus, because the attraction between the wall and the water is stronger than the water's internal cohesion. Meniscus in mercury (left) and water compared. Adhesive forces between the molecules of a liquid and different molecules composing a surface in contact with the liquid are responsible for phenomena such as surface wetting and capillary rise. A convex meniscus occurs when the molecules have a stronger attraction to each other than to the container, as with mercury and glass. How is the meniscus of mercury different to that of water? The cookies is used to store the user consent for the cookies in the category "Necessary". For every one silicon atom, This is a convex, convex meniscus. Larger drops are more greatly affected by gravity, air resistance, surface interactions, and so on, and as a result, are less spherical. The cookie is used to store the user consent for the cookies in the category "Analytics". higher near the container than it is when you're Mercury therefore does not wet glass, and it forms a convex meniscus when confined in a tube because the cohesive forces within the mercury tend to draw it into a drop (Figure \(\PageIndex{4}\)). concave, concave meniscus. Correct option: (3) Force of cohesion, between water molecules, is less that n the force of adhesion between water and glass; the reverse is true for mercury. If you were take that same glass beaker, instead of filling it with water if you filled it with say, mercury. The viscosity of a liquid is a measure of its resistance to flow. up this thin glass tube. you have two oxygen atoms. Mercury When mercury is placed in a graduated cylinder, the cohesive forces in the mercury are stronger than the adhesive forces between the mercury and the glass. This occurs with water and a glass tube. The surface tension is quite a major effect. On the other hand, the cohesive forces between mercury atoms are much greater than the adhesive forces between mercury and glass. The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Just google those terms and you will learn. Posted 8 years ago. Some insects, like the one shown in Figure \(\PageIndex{3}\), even though they are denser than water, move on its surface because they are supported by the surface tension. And actually it would be very hard to find something that thin that's on the order of only a few molecules. As Table \(\PageIndex{1}\) shows, the more structurally complex are the molecules in a liquid and the stronger the IMFs between them, the more difficult it is for them to move past each other and the greater is the viscosity of the liquid. "You're telling me that The water is seen to curve up the edge of the glass. If you filled it with mercury, you would get a meniscus that looks like this where there's a bulge near the center when you're further away from the container than when you're at the container. Please contact your Account Manager if you have any query. And in particular this meniscus, because the fluid is of silicon oxide lattice. Some liquids, like the element mercury (Hg), form a convex meniscus, meaning that it is shaped like a lower-case n (see Fig. Click here. The IMFs of attraction between two different molecules are called adhesive forces. $\endgroup$ Glass, typically made up For a sufficiently narrow tube with circular cross-section, the shape of the meniscus will approximate a section of a spherical surface, while for a large container, most of the upper surface of the liquid will be almost flat, only curving up (if concave) or down (if convex) near the edges. I am telling you that." That's why you'll see A small tube has a relatively large surface area for a given volume of blood, which results in larger (relative) attractive forces, allowing the blood to be drawn farther up the tube. For example, water does not wet waxed surfaces or many plastics such as polyethylene. on a very thin glass tube. Beyond the fact that You should always measure light liquids at the bottom of the meniscus and . Then it gets bumped the right way. Actually it depends on the liquid itself and chemical bonding. GB 340 7410 88. 1550520. Helmenstine, Anne Marie, Ph.D. (2020, August 28). University of Illinois at Urbana-Champaign. The LibreTexts libraries arePowered by NICE CXone Expertand are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Powered by SiteManager | Contact Webmaster. Explain. When a tube of a narrow bore, often called a capillary tube, is dipped into a liquid and the liquid wets the tube (with zero contact angle), the liquid surface inside the tube forms a concave meniscus, which is a virtually spherical surface having the same radius, r, as the inside of the tube. partial positive charges form at the silicon You will still see a meniscus but because the salt water disturbs the surface tension of water, the meniscus too will be different -- this is hopefully nto surprising. The molecules within a liquid are surrounded by other molecules and are attracted equally in all directions by the cohesive forces within the liquid. If the adhesive forces between water molecules and the molecules of the surface are weak compared to the cohesive forces between the water molecules, the water does not wet the surface. (credit photo: modification of work by Mark Blaser). CHARLES D. WINTERS/SCIENCE PHOTO LIBRARY And it's really just this You depend on a constant supply of tears to keep your eyes lubricated and on capillary action to pump tear fluid away. Direct link to Ivana - Science trainee's post Exactly! Legal. ThoughtCo. Water is strongly attracted to glass and its meniscus is concave (adhesion). These cookies track visitors across websites and collect information to provide customized ads. A concave meniscus occurs when the attraction between the particles of the liquid and the container (adhesion) is more than half the attraction of the particles of the liquid to each other (cohesion), causing the liquid to climb the walls of the container (see surface tension#Causes). But when you pour syrup on pancakes or add oil to a car engine, you note that syrup and motor oil do not flow as readily. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. https://www.thoughtco.com/how-to-read-a-meniscus-606055 (accessed May 1, 2023). However, the molecules on the surface of a liquid are attracted only by about one-half as many molecules. hydrogen bonding to form and that's what kind of gives water all of these special properties. On the other hand, for mercury, cohesive . the liquid, prefering a spherical shape. Glass is electrically polarizable, and attracts charged observe this and to name them. It can be either convex or concave. And there's actually capillary action inside of our capillaries. Retrieved from https://www.thoughtco.com/how-to-read-a-meniscus-606055. And that causes this And just to be clear what's The rise of a liquid in the capillary tube is due to the surface tension. When water is confined in a glass tube, its meniscus (surface) has a concave shape because the water wets the glass and creeps up the side of the tube. Why does mercury have a convex meniscus while water is concave? Figure \(\PageIndex{4}\): Differences in the relative strengths of cohesive and adhesive forces result in different meniscus shapes for mercury (left) and water (right) in glass tubes. Figure \(\PageIndex{6}\): Depending upon the relative strengths of adhesive and cohesive forces, a liquid may rise (such as water) or fall (such as mercury) in a glass capillary tube. Well sure, you can have a convex meniscus. If you were take that same glass beaker, instead of filling it with water if you filled it with say, mercury. Share sensitive information only on official, secure websites. When reading a depth scale on the side of an instrument filled with liquid, such as a water level device, the meniscus must be taken into account in order to obtain an accurate measurement. Science Photo Library (SPL) something on your counter. http://water.usgs.gov/edu/capillaryaction.html, https://chemistry.stackexchange.com/questions/30791/why-is-sand-glass-polar-how-does-lattice-structure-change-polarity, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5024753/. These are examples of capillary actionwhen a liquid flows within a porous material due to the attraction of the liquid molecules to the surface of the material and to other liquid molecules. University of Illinois at Urbana-Champaign, Absorption and scattering of light in air. Then, when the open end of a narrow-diameter glass tube touches the drop of blood, the adhesive forces between the molecules in the blood and those at the glass surface draw the blood up the tube. As the raindrop falls, it loses that rounded shape. Water-based fluids like sap, honey, and milk also have a concave meniscus in glass or other wettable containers. Adhesion between the liquid This is because dissolved salts can increase the surface tension of water. A concave meniscus, which is what you normally will see, occurs when the molecules of the liquid are attracted to those of the container. When your finger is pricked, a drop of blood forms and holds together due to surface tensionthe unbalanced intermolecular attractions at the surface of the drop. You can find out more about our use, change your default settings, and withdraw your consent at any time with effect for the future by visiting Cookies Settings, which can also be found in the footer of the site.
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