Which Best Explains the High Surface Tension of Water

Which Best Explains the High Surface Tension of Water.

Chapter 2: Introduction to the Chemistry of Life

two.two Water

By the end of this section, yous will be able to:

  • Draw the backdrop of water that are critical to maintaining life

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Practice y’all ever wonder why scientists spend time looking for h2o on other planets? Information technology is considering water is essential to life; even minute traces of it on another planet tin bespeak that life could or did exist on that planet. H2o is one of the more than abundant molecules in living cells and the ane most disquisitional to life as we know it. Approximately 60–seventy percent of your torso is made upwardly of water. Without it, life simply would not exist.

Water Is Polar

The hydrogen and oxygen atoms inside h2o molecules grade polar covalent bonds. The shared electrons spend more than time associated with the oxygen cantlet than they do with hydrogen atoms. In that location is no overall charge to a water molecule, but in that location is a slight positive charge on each hydrogen cantlet and a slight negative charge on the oxygen atom. Because of these charges, the slightly positive hydrogen atoms repel each other and form the unique shape. Each water molecule attracts other h2o molecules because of the positive and negative charges in the dissimilar parts of the molecule. H2o also attracts other polar molecules (such as sugars), forming hydrogen bonds. When a substance readily forms hydrogen bonds with water, it can dissolve in water and is referred to as
(“water-loving”). Hydrogen bonds are not readily formed with nonpolar substances like oils and fats . These nonpolar compounds are
(“water-fearing”) and volition non deliquesce in h2o.

Figure 2.7 As this macroscopic image of oil and h2o shows, oil is a nonpolar compound and, hence, will not dissolve in water. Oil and h2o do not mix.

Water Stabilizes Temperature

The hydrogen bonds in water allow it to absorb and release heat energy more slowly than many other substances.
is a measure of the movement (kinetic energy) of molecules. As the move increases, free energy is higher and thus temperature is higher. H2o absorbs a nifty deal of energy before its temperature rises. Increased energy disrupts the hydrogen bonds between water molecules. Because these bonds can be created and disrupted rapidly, water absorbs an increase in energy and temperature changes only minimally. This means that h2o moderates temperature changes inside organisms and in their environments. Equally free energy input continues, the balance between hydrogen-bond formation and destruction swings toward the destruction side. More bonds are broken than are formed. This process results in the release of individual h2o molecules at the surface of the liquid (such as a body of water, the leaves of a plant, or the skin of an organism) in a process called
evaporation. Evaporation of sweat, which is xc percent h2o, allows for cooling of an organism, because breaking hydrogen bonds requires an input of energy and takes heat away from the body.

Conversely, equally molecular move decreases and temperatures drop, less energy is present to break the hydrogen bonds betwixt water molecules. These bonds remain intact and begin to form a rigid, lattice-like structure (e.thou., ice) (Effigy 2.8
a). When frozen, ice is less dumbo than liquid water (the molecules are farther autonomously). This ways that ice floats on the surface of a body of water (Effigy two.8
b). In lakes, ponds, and oceans, ice volition grade on the surface of the water, creating an insulating barrier to protect the animal and institute life below from freezing in the water. If this did not happen, plants and animals living in water would freeze in a cake of ice and could not move freely, making life in cold temperatures difficult or impossible.

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Part A shows the lattice-like molecular structure of ice. Part B is a photo of ice on water.
Figure 2.viii (a) The lattice construction of ice makes information technology less dense than the freely flowing molecules of liquid water. Ice’s lower density enables information technology to (b) float on water. (credit a: modification of work by Jane Whitney; credit b: modification of work by Carlos Ponte)

Water Is an Excellent Solvent

Considering water is polar, with slight positive and negative charges, ionic compounds and polar molecules can readily dissolve in it. H2o is, therefore, what is referred to as a
solvent—a substance capable of dissolving another substance. The charged particles will grade hydrogen bonds with a surrounding layer of water molecules. This is referred to as a sphere of hydration and serves to keep the particles separated or dispersed in the water. In the instance of table salt (NaCl) mixed in water, the sodium and chloride ions split, or dissociate, in the water, and spheres of hydration are formed effectually the ions. A positively charged sodium ion is surrounded past the partially negative charges of oxygen atoms in h2o molecules. A negatively charged chloride ion is surrounded by the partially positive charges of hydrogen atoms in water molecules. These spheres of hydration are as well referred to as hydration shells. The polarity of the water molecule makes it an effective solvent and is important in its many roles in living systems.

Illustration of spheres of hydration around sodium and chlorine ions.
Figure two.ix When salt (NaCl) is mixed in water, spheres of hydration form around the ions.

Water Is Cohesive

Accept you ever filled upwards a glass of water to the very summit and so slowly added a few more drops? Earlier it overflows, the h2o actually forms a dome-similar shape above the rim of the glass. This water tin can stay to a higher place the drinking glass because of the property of
cohesion. In cohesion, water molecules are attracted to each other (considering of hydrogen bonding), keeping the molecules together at the liquid-air (gas) interface, although at that place is no more room in the glass. Cohesion gives rise to
surface tension, the chapters of a substance to withstand rupture when placed under tension or stress. When yous drop a small scrap of paper onto a droplet of water, the paper floats on summit of the water droplet, although the object is denser (heavier) than the water. This occurs because of the surface tension that is created by the water molecules. Cohesion and surface tension proceed the water molecules intact and the item floating on the acme. It is even possible to “float” a steel needle on summit of a glass of water if you lot identify information technology gently, without breaking the surface tension.

Picture of a needle floating on top of water because of cohesion and surface tension.
Effigy 2.10 The weight of a needle on top of water pulls the surface tension downwardly; at the same fourth dimension, the surface tension of the water is pulling it up, suspending the needle on the surface of the h2o and keeping it from sinking. Notice the indentation in the h2o around the needle.

These cohesive forces are besides related to the water’southward property of
adhesion, or the attraction betwixt water molecules and other molecules. This is observed when water “climbs” upwards a harbinger placed in a glass of water. You will notice that the water appears to be college on the sides of the straw than in the middle. This is because the water molecules are attracted to the harbinger and therefore adhere to it.

Cohesive and adhesive forces are important for sustaining life. For instance, considering of these forces, water tin can flow up from the roots to the tops of plants to feed the plant.

Buffers, pH, Acids, and Bases

The pH of a solution is a measure of its acidity or alkalinity. You accept probably used
litmus paper, paper that has been treated with a natural water-soluble dye so information technology can be used as a pH indicator, to test how much acid or base (alkalinity) exists in a solution. You might accept even used some to make sure the water in an outdoor swimming pool is properly treated. In both cases, this pH test measures the amount of hydrogen ions that exists in a given solution. Loftier concentrations of hydrogen ions yield a low pH, whereas low levels of hydrogen ions result in a high pH. The overall concentration of hydrogen ions is inversely related to its pH and can be measured on the
pH calibration
(Figure 2.xi). Therefore, the more than hydrogen ions nowadays, the lower the pH; conversely, the fewer hydrogen ions, the higher the pH.

The pH calibration ranges from 0 to 14. A change of one unit on the pH scale represents a alter in the concentration of hydrogen ions by a factor of 10, a change in ii units represents a modify in the concentration of hydrogen ions by a factor of 100. Thus, small changes in pH stand for large changes in the concentrations of hydrogen ions. Pure water is neutral. It is neither acidic nor basic, and has a pH of 7.0. Anything beneath 7.0 (ranging from 0.0 to vi.ix) is acidic, and annihilation in a higher place vii.0 (from 7.1 to 14.0) is alkaline. The blood in your veins is slightly element of group i (pH = seven.4). The environment in your stomach is highly acidic (pH = 1 to 2). Orange juice is mildly acidic (pH = approximately 3.5), whereas baking soda is basic (pH = 9.0).


The pH scale with representative substances and their pHs.
Figure 2.11 The pH scale measures the amount of hydrogen ions (H+) in a substance.

are substances that provide hydrogen ions (H+) and lower pH, whereas
provide hydroxide ions (OH) and raise pH. The stronger the acrid, the more than readily it donates H+. For example, hydrochloric acid and lemon juice are very acidic and readily give up H+
when added to water. Conversely, bases are those substances that readily donate OH. The OH
ions combine with H+
to produce water, which raises a substance’s pH. Sodium hydroxide and many household cleaners are very element of group i and give up OH
rapidly when placed in water, thereby raising the pH.

Near cells in our bodies operate within a very narrow window of the pH calibration, typically ranging simply from 7.2 to 7.6. If the pH of the body is outside of this range, the respiratory arrangement malfunctions, equally do other organs in the body. Cells no longer function properly, and proteins will interruption downwards. Deviation outside of the pH range tin induce coma or even cause expiry.

Then how is information technology that we tin ingest or inhale acidic or bones substances and not die? Buffers are the cardinal.
readily absorb backlog H+
or OH, keeping the pH of the body carefully maintained in the same narrow range. Carbon dioxide is part of a prominent buffer system in the homo body; it keeps the pH inside the proper range. This buffer organisation involves carbonic acrid (HiiCO3) and bicarbonate (HCO3
) anion. If also much H+
enters the body, bicarbonate volition combine with the H+
to create carbonic acid and limit the decrease in pH. Too, if too much OH
is introduced into the arrangement, carbonic acid will apace dissociate into bicarbonate and H+
ions. The H+
ions can combine with the OH
ions, limiting the increase in pH. While carbonic acid is an important production in this reaction, its presence is fleeting because the carbonic acid is released from the trunk as carbon dioxide gas each time we breathe. Without this buffer system, the pH in our bodies would fluctuate besides much and we would neglect to survive.

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Section Summary

Water has many properties that are critical to maintaining life. It is polar, allowing for the formation of hydrogen bonds, which allow ions and other polar molecules to deliquesce in water. Therefore, water is an fantabulous solvent. The hydrogen bonds betwixt water molecules requite water the power to hold heat ameliorate than many other substances. As the temperature rises, the hydrogen bonds between water continually break and reform, allowing for the overall temperature to remain stable, although increased energy is added to the system. Water’s cohesive forces let for the property of surface tension. All of these unique properties of water are important in the chemistry of living organisms.

The pH of a solution is a measure of the concentration of hydrogen ions in the solution. A solution with a high number of hydrogen ions is acidic and has a depression pH value. A solution with a high number of hydroxide ions is basic and has a loftier pH value. The pH scale ranges from 0 to 14, with a pH of 7 beingness neutral. Buffers are solutions that moderate pH changes when an acid or base is added to the buffer system. Buffers are important in biological systems because of their ability to maintain constant pH weather condition.

a substance that donates hydrogen ions and therefore lowers pH

the attraction betwixt water molecules and molecules of a different substance

a substance that absorbs hydrogen ions and therefore raises pH

a solution that resists a change in pH by arresting or releasing hydrogen or hydroxide ions

the intermolecular forces between water molecules caused by the polar nature of water; creates surface tension

the release of water molecules from liquid water to form h2o vapor

describes a substance that dissolves in water; water-loving

describes a substance that does not dissolve in water; h2o-fearing

litmus paper:
filter paper that has been treated with a natural water-soluble dye and so it can exist used as a pH indicator

pH scale:
a scale ranging from 0 to 14 that measures the approximate concentration of hydrogen ions of a substance

a substance capable of dissolving another substance

surface tension:
the cohesive forcefulness at the surface of a body of liquid that prevents the molecules from separating

a mensurate of molecular move


Humphrey, W., Dalke, A. and Schulten, Yard., “VMD—Visual Molecular Dynamics”,
J. Molec. Graphics, 1996, vol. 14, pp. 33-38. http://www.ks.uiuc.edu/Research/vmd/

Media Attribution

  • Figure 2.7 by Gautam Dogra
  • Figure 2.viii
    • water ice lattice past Jane Whitney
    • (b) by Carlos Ponte
  • Figure two.10 by Cory Zanker
  • Figure ii.11 past Edward Stevens

Which Best Explains the High Surface Tension of Water

Source: https://opentextbc.ca/biology/chapter/2-2-water/

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