Viscosity, Surface Tension and Temperature | Science project | ddttrh.info
A discussion of cohesive forces and surface tension is included, as well as surface acting agents Engineering Connection more energy to maintain due to the molecular forces associated with surface tension. Learning Objectives. It explains the basic properties of liquids, and explores how intermolecular forces determine their behavior. The concepts of cohesion, adhesion, and viscosity. Is there any relation between surface tension and viscosity? The purpose of my science fair project is to prove that as temperature increases, viscosity and surface tension The strength of surface tension depends on intermolecular forces.
Consider the ease with which you can pour yourself a glass of water, as compared to the relative challenge of pouring thick, slow-moving motor oil into an engine. The difference is their viscosityor resistance to flow. Motor oil is quite viscous ; water, not so much. Remember, water molecules form strong hydrogen bonds with each other.
Pentane, on the other hand, made up of just hydrogen and carbon atoms, is nonpolar, so the only types of intermolecular forces it can form are the relatively weak London dispersion forces. The weaker intermolecular forces mean that the molecules can more easily move past each other, or flow — hence, lower viscosity.
But both water and pentane are relatively small molecules. For example, compare pentane to motor oil, which is a complex mixture of large hydrocarbons much larger than little pentane, and some with dozens or even hundreds of carbons in a chain. Both liquids are nonpolar, and so have relatively weak intermolecular forces ; the difference is the size.
Surface Tension Basics - Lesson - TeachEngineering
The big, bendy motor oil hydrocarbons can literally get tangled with their neighbors, which slows the flow. Group A consists of large molecules in a tangled blob a viscous liquid and Group B consists of smaller molecules with fewer entanglements a less viscous liquid.
Returning to our original comparison of motor oil versus water, even though water has such strong intermolecular forcesthe much larger size of the molecules in the motor oil makes the oil more viscous. This is the case because temperature affects both of the factors that determine viscosity in the first place. It also makes the molecules move around more, so those big molecules that got tangled up when they were cold become more dynamic and are more able to slide past each other, allowing the liquid to flow more easily.
Comprehension Checkpoint Motor oil pours more slowly than the solvent pentane because motor oil is made up of a. Complex liquids When you think of water, you might think of its chemical formulaH2O. This formula describes a pure liquid composed only of H2O molecules, with absolutely no other components. The reality, though, is that the vast majority of liquids we encounter are complex mixtures of many compounds.
Solutions are made of a liquid solvent in which one or more solutes are dissolved. Solutes can be solidsliquidsand gases. There are many, many common solutions that use water as the solvent, including salt water and pretty much any type of flavored drink.
Carbon dioxide CO2 gas is a common gaseous solute in carbonated drinks, and ethanol is a liquid solute in any alcoholic drink.
Although solutions are mixtures of multiple compounds, the properties discussed in the previous section still apply. Not all solutes dissolve in all solvents. You can dissolve huge amounts of some solutes in some liquidsand other solutes are only marginally soluble in any solvent. For example, oil-based and therefore nonpolar paints require a non-polar solvent such as turpentine for clean up; they will not dissolve in water, which is polar.
Table salt or sugar, on the other hand, both polar solidseasily dissolve at high concentrations in water. More complex solutions include emulsionscolloidsand suspensions. Mayonnaise, for example, is an emulsion of oil, egg yolk, and vinegar or lemon juice, which is made by very vigorous mixing.
Colloids and suspensions both consist of insoluble particles in a liquid. And a suspension, on the other hand, is a liquid that contains larger insoluble particles that will eventually separate.
Milk is a useful example of the difference between these two. Fresh milk is a suspension. Remember the separation of vinegar and oil in salad dressing?
The milk separation process is similar, with the oily fat separating from the water. The milk at most grocery stores, on the other hand, is a colloid. Comprehension Checkpoint Which statement is true about solutes? Solutes are always liquids. Solutes can be solids, liquids, or gases. But in addition to this already wide variety, there are some substances that blur the distinction between liquid and solid. For example, as a kid you may have played with oobleck, a mixture of water and starch that gets its name from a Dr.
Oobleck is a slimy substance that can flow between your fingers if you hold it gently in your hands but becomes hard and firm, almost solid, if you squeeze it. For a more technical example, consider the material used in LCD television displays and other electronic screens. These ink droplets are first charged and then directed into position by charged deflection plates. The surface tension of the ink is vital for this process to work: In a continuous inkjet printer, a jet of ink forms droplets that are deflected to the correct position.
By using an ink with metallic particles, circuits can printed onto a variety of substrates. Specially designed inkjet devices paint automobiles and apply decorations to irregular or rounded objects. Ink jet printing has already begun to replace screen printing in textiles and ceramics because of advantages in speed, choice of design, and ease of use.
Inkjet printing is also used to create 3D prototypes of computer-generated objects. Changing Surface Tension Figure 6. Surfactants are added to paints and inks to lower surface tension so they flow freely, and used in the oil industry to aid in extraction.Surface Tension (Intermolecular Forces)
Xchng, and Eric Kounce, Wikimedia Commons http: JPG Under certain conditions, it is desirable to lower the surface tension. A high surface tension encourages a liquid to bead rather than spread evenly across a surface. For this reason surface-active agents, or surfactants, are used for various applications to lower the surface tensions of liquids. Inks and paints see Figure 6 are everyday examples in which lowering surface tension is useful in making liquids spread.
Using surfactants to lower surface tension is also used in the oil industry. Surface tension causes oil to become trapped in the pores of the containing rock due to a phenomenon called capillary action. By adding surfactants to the oil deposit, it helps the oil release from the pores and become available for extraction see Figure 6. Finally, certain semi-aquatic insects release surfactants for locomotion. The released surfactant lowers the surface tension behind them, and the insects are pulled forward by the stronger surface tension in the untreated water ahead of them.
The property of the surface of a liquid that allows it to resist an external force. This property is caused by cohesion of like molecules and explains many of the behaviors of liquids.
Associated Activities Surface Tension Lab - Students design and test water and soap solutions for making bubbles. They experiment with additives to their best "recipes" to enhance the bubbles. In a math homework, students perform calculations that explain why soap bubbles form spheres. Ask the students and discuss as a class: How do water bugs walk on the surface of the water? The water molecules are pulled inwards and create a slightly thicker film on the surface that acts like a springy membrane.
The water bug can walk on top of this surface. We call this phenomenon surface tension. Why do soap bubbles form spheres instead of cubes? Students will find out during this lesson and associated activity. This is the result of a relationship between the volume of air inside the bubble and the surface area of the soap film of the bubble. The surface tension tries to minimize the surface area.
11.4: Intermolecular Forces in Action: Surface Tension, Viscosity, and Capillary Action
For the same volume of air, a sphere has a smaller surface area than a cube. What happens when a soap bubble pops? The trapped air is released and the surface tension pulls the water into water droplets. Why does a stream of water form droplets as it falls? Again, the water droplets have a smaller surface area than the column of water, so the surface tension causes the water to form droplets.
Ask students to imagine that they are water molecules and describe what is happening to them in the situations below. Have them draw illustrations to go along with their descriptions. You are in the middle of a water drop. You are on the surface of a water drop. You are in a soap bubble. This is a bit tricky and a good challenge to see if students really understand. A soap bubble is actually made of two surfaces, inside and outside of the bubble. Both surfaces are trying to make the bubble as small as possible, hence the spherical shape, but the air trapped inside the bubble means the bubble cannot squeeze down into a simple water droplet.
To reinforce ideas about surface tension, have students form two circles, one inside the other. Arrange for equal or close to equal numbers of students in both circles. Have students in each circle face their "partners" in the other circle. Have the students of one circle to explain one of the concepts listed below to their partners in the other circle, and then the partners explain the concepts back to them.
Between questions, have the two circles move in opposite directions so that partners are changed. If students have trouble explaining a concept, change partners and repeat the same question.
What is surface tension? Why does surface tension try to minimize surface area? What do they do? Additional Multimedia Support See short, high-speed camera videos of inkjet printers posted to youtube by user imagexpertinc, at: References Bush, John W. Biolocomotion at the Interface. Includes a discussion on how insects move on the surface of the water including water-walking, meniscus climbing and Marangoni [surfactant] propulsion.
Science in the Box, Proctor and Gamble. Accessed August 17, Explanation of surfactants http: Capillarity and Wetting Phenomena: