Liquid Basics• Liquids are an in-between state of matter.• They can be found between the solid and gas states. They are not made up of the same molecules.• Often called a condensed phase because their particles are close together.• They will always take the shape of the container it occupies.• Example: If some water (H2O) is poured into a cup, it will fill up the bottom of the cup first and then fill the rest. The water will also take the shape of the cup.• The top part of a liquid will usually have a flat surface. That flat surface is the result of gravity pulling on the molecules.• Example: Putting an ice cube (solid) into a cup will leave a cube in the middle of the cup because it is a solid. The shape of the solid cube wont change until the ice becomes a liquid.
• Liquids are also difficult to compress.• (When something is compressed, a certain amount of material is measured out and forced into a smaller space.)• Solids are very difficult to compress and gases are very easy. Liquids are in the middle, but tend to be difficult.• When something is compressed, the atoms are forced together. When the pressure goes up, substances are compressed. Liquids already have their atoms close together, so they are hard to compress.• Many shock absorbers in cars compress liquids in sealed tubes.
Specific Liquid Properties• Viscosity - The resistance of a liquid to flow is called its viscosity.• Surface Tension - The result of attraction between molecules of a liquid which causes the surface of the liquid to act as a thin elastic film under tension. Surface tension causes water to form spherical drops.• Vapor Pressure - The pressure that a solid or liquid exerts when it is in equilibrium with its vapor at a given temperature.• Boiling Point - When vapor pressure equals atmospheric pressure.• Freezing Point – It is the temperature at which the liquid form of the substance becomes a solid.• Capillary action – It occurs when the attraction of a liquid’s molecules for themselves differs from their attraction for a solid that the liquid contacts.• Miscibility – It is a measure of how easily different liquids will dissolve when mixed together.• Osmosis – It occurs when molecules of the initial liquid pass through a membrane, but molecules of the dissolved substance d do not.
Viscosity• Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress.• Viscosity sometimes is also "thickness" or "internal friction".• For example, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity.• Put simply, the less viscous the fluid is, the greater its ease of movement (fluidity).• Viscosity describes a fluids internal resistance to flow and may be thought of as a measure of fluid friction.• For example, high-viscosity felsic magma will create a tall, steep stratovolcano, because it cannot flow far before it cools, while low-viscosity mafic lava will create a wide, shallow-sloped shield volcano.
• Here is a simulation of substances with different viscosities.• As observed, the substance above demonstrates that it has lower viscosity than the substance below as two objects are dropped into them.
Surface Tension• Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force.• For example, in the floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface.• This property is caused by cohesion of similar molecules, and is responsible for many of the behaviors of liquids.• Surface tension has the dimension of force per unit length, or of energy per unit area.
• Water molecules want to cling to each other. At the surface, however, there are fewer water molecules to cling to since there is air above (thus, no water molecules). This results in a stronger bond between those molecules that actually do come in contact with one another, and a layer of strongly bonded water. This surface layer (held together by surface tension) creates a considerable barrier between the atmosphere and the water.
Vapor Pressure• Vapor pressure is the pressure exerted by vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system.• The equilibrium vapor pressure is an indication of a liquids evaporation rate. It relates to the tendency of particles to escape from the liquid (or a solid).• The vapor pressure of any substance increases non-linearly with temperature.• The boiling point of a liquid is the temperature at which the vapor pressure equals the ambient atmospheric pressure.
Boiling Point• The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.• Example: A liquid in a vacuum has a lower boiling point than when that liquid is at atmospheric pressure.• A liquid at high-pressure has a higher boiling point than when that liquid is at atmospheric pressure.• In other words, the boiling point of a liquid varies depending upon the surrounding environmental pressure. For a given pressure, different liquids boil at different temperatures.• Sometimes a liquid can be superheated—that is, heated above its usual boiling point without changing into vapor.• Superheating occurs when vapor bubbles inside a liquid don’t have an appropriate surface on which to form.
Freezing Point• The freezing point of a substance is the temperature at which the liquid form of the substance becomes a solid. The molecules of a liquid arrange into a more ordered structure as the liquid freezes. The freezing point of a substance is essentially the same as its melting point—that is, the point at which a solid becomes a liquid.• In ice, each water molecule is solidly packed into a lattice, surrounded by four molecules equally distant from each other. This structure is actually less dense than the molecular patterns that can occur in the liquid form of water, which is why ice floats on water.
Capillary Action• This occurs when the attraction of a liquid’s molecules for themselves differs from their attraction for a solid that the liquid contacts.• For example: Water will climb up a paper towel if the edge of the towel touches a puddle, and it will climb up a thin glass tube if the tube is dipped in water.• The water in the paper towel example climbs the towel because the water molecules are more attracted to the paper than they are to each other.
• Water molecules, for instance, are more attracted to glass than they are to one another. Water will therefore climb up a narrow glass tube that is dipped into a beaker of water, because the water would rather be in contact with the glass than with itself. Mercury molecules, on the other hand, are more attracted to each other than they are to glass. Mercury will avoid contact with a narrow glass tube that is dipped into a beaker of mercury.
Miscibility• Miscibility is a measure of how easily different liquids will dissolve when mixed together.• Miscibility depends on the polarity of a liquid’s molecules.• For example, water will mix with alcohol because they are both polar liquids, so their molecules attract one another. But water will not mix well with oil, which is a nonpolar liquid. Oil floats on top of water because the polar water molecules are much more strongly attracted to each other than to the oil molecules.• The rule for determining miscibility is that ―like dissolves like.‖ Polar liquids are miscible with other polar liquids, while nonpolar liquids are miscible with other nonpolar liquids.
Osmosis• Osmosis occurs when molecules of the initial liquid pass through a membrane, but molecules of the dissolved substance do not.• The molecules of the initial liquid can pass through the membrane because they are relatively small.• Osmosis tends to equalize the concentration of the solutions on both sides of a membrane. The membrane in this case is called semipermeable, because it allows one part of the mixture to pass through but not another.
• The experiment shown above demonstrates the process of osmosis. Water flows through a semipermeable membrane into a sugar solution, diluting the solution. The sugar molecules cannot pass through the membrane, so the water outside remains pure.