Chapter 2 Active Reading Section 2.2 Water and Solutions Answer Key Chemistry of Life
Chapter ii: Introduction to the Chemical science of Life
2.ii Water
By the stop of this section, y'all volition exist able to:
- Describe the properties of water that are disquisitional to maintaining life
Sentry a video about why we need oxygen and how information technology causes problems for living things.
Practise you e'er wonder why scientists spend fourth dimension looking for water on other planets? It is because h2o is essential to life; even minute traces of it on another planet can indicate that life could or did exist on that planet. Water is one of the more abundant molecules in living cells and the one nearly critical to life as nosotros know it. Approximately 60–70 percent of your trunk is made up of h2o. Without it, life simply would not exist.
H2o Is Polar
The hydrogen and oxygen atoms within water molecules course polar covalent bonds. The shared electrons spend more than time associated with the oxygen atom than they do with hydrogen atoms. In that location is no overall charge to a water molecule, but there is a slight positive charge on each hydrogen atom and a slight negative accuse on the oxygen atom. Because of these charges, the slightly positive hydrogen atoms repel each other and course the unique shape. Each water molecule attracts other h2o molecules because of the positive and negative charges in the unlike parts of the molecule. Water also attracts other polar molecules (such as sugars), forming hydrogen bonds. When a substance readily forms hydrogen bonds with water, it tin deliquesce in water and is referred to as hydrophilic ("h2o-loving"). Hydrogen bonds are non readily formed with nonpolar substances like oils and fats . These nonpolar compounds are hydrophobic ("h2o-fearing") and will non dissolve in water.
Water Stabilizes Temperature
The hydrogen bonds in water allow it to absorb and release heat free energy more than slowly than many other substances. Temperature is a measure of the movement (kinetic energy) of molecules. Every bit the motion increases, energy is higher and thus temperature is higher. Water absorbs a cracking bargain of energy before its temperature rises. Increased energy disrupts the hydrogen bonds betwixt water molecules. Considering these bonds can be created and disrupted rapidly, water absorbs an increase in free energy and temperature changes only minimally. This means that water moderates temperature changes within organisms and in their environments. Equally energy input continues, the residual between hydrogen-bond germination and destruction swings toward the destruction side. More bonds are cleaved than are formed. This process results in the release of individual h2o molecules at the surface of the liquid (such equally a trunk of water, the leaves of a plant, or the pare of an organism) in a process called evaporation. Evaporation of sweat, which is 90 pct water, allows for cooling of an organism, because breaking hydrogen bonds requires an input of free energy and takes estrus away from the trunk.
Conversely, as molecular motility decreases and temperatures drib, less energy is present to break the hydrogen bonds between water molecules. These bonds remain intact and begin to form a rigid, lattice-like structure (east.k., ice) (Figure two.eight a). When frozen, ice is less dense than liquid water (the molecules are farther apart). This means that water ice floats on the surface of a trunk of h2o (Figure ii.8 b). In lakes, ponds, and oceans, ice will form on the surface of the water, creating an insulating barrier to protect the fauna and found life beneath from freezing in the water. If this did not happen, plants and animals living in water would freeze in a block of ice and could not motility freely, making life in cold temperatures hard or incommunicable.
Water Is an Fantabulous Solvent
Because water is polar, with slight positive and negative charges, ionic compounds and polar molecules can readily deliquesce in it. Water is, therefore, what is referred to as a solvent—a substance capable of dissolving another substance. The charged particles will form hydrogen bonds with a surrounding layer of h2o molecules. This is referred to as a sphere of hydration and serves to keep the particles separated or dispersed in the water. In the case of table salt (NaCl) mixed in water, the sodium and chloride ions separate, or dissociate, in the h2o, and spheres of hydration are formed around the ions. A positively charged sodium ion is surrounded by the partially negative charges of oxygen atoms in water molecules. A negatively charged chloride ion is surrounded past the partially positive charges of hydrogen atoms in h2o molecules. These spheres of hydration are as well referred to as hydration shells. The polarity of the h2o molecule makes information technology an effective solvent and is important in its many roles in living systems.
Water Is Cohesive
Take you ever filled up a glass of water to the very top and then slowly added a few more than drops? Before it overflows, the water actually forms a dome-similar shape above the rim of the glass. This water can stay higher up the glass considering 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 there is no more room in the drinking glass. Cohesion gives rise to surface tension, the capacity of a substance to withstand rupture when placed nether tension or stress. When you drop a small fleck of paper onto a droplet of water, the paper floats on elevation of the h2o droplet, although the object is denser (heavier) than the water. This occurs because of the surface tension that is created past the water molecules. Cohesion and surface tension proceed the water molecules intact and the item floating on the tiptop. It is even possible to "float" a steel needle on superlative of a glass of h2o if you place information technology gently, without breaking the surface tension.
These cohesive forces are also related to the water'south belongings of adhesion, or the attraction between water molecules and other molecules. This is observed when h2o "climbs" upwardly a harbinger placed in a glass of water. You will find that the water appears to be college on the sides of the harbinger than in the centre. This is because the water molecules are attracted to the straw and therefore adhere to information technology.
Cohesive and adhesive forces are important for sustaining life. For case, because of these forces, h2o can period up from the roots to the tops of plants to feed the plant.
Concept in Action
To learn more well-nigh water, visit the U.South. Geological Survey Water Science for Schools: All About H2o! website.
Buffers, pH, Acids, and Bases
The pH of a solution is a measure of its acerbity or alkalinity. You have probably used litmus paper, paper that has been treated with a natural h2o-soluble dye so information technology tin can be used equally a pH indicator, to exam how much acid or base (alkalinity) exists in a solution. You might have even used some to make certain 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. High 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 exist measured on the pH scale (Figure two.11). Therefore, the more hydrogen ions present, the lower the pH; conversely, the fewer hydrogen ions, the higher the pH.
The pH scale ranges from 0 to fourteen. A change of one unit of measurement on the pH scale represents a change in the concentration of hydrogen ions by a cistron of 10, a alter in ii units represents a change in the concentration of hydrogen ions by a gene of 100. Thus, minor changes in pH represent large changes in the concentrations of hydrogen ions. Pure water is neutral. It is neither acidic nor basic, and has a pH of vii.0. Anything below 7.0 (ranging from 0.0 to six.nine) is acidic, and anything higher up 7.0 (from vii.one to fourteen.0) is alkaline. The claret in your veins is slightly alkaline (pH = 7.4). The surround in your tummy is highly acidic (pH = 1 to 2). Orange juice is mildly acidic (pH = approximately iii.5), whereas blistering soda is basic (pH = 9.0).
Acids are substances that provide hydrogen ions (H+) and lower pH, whereas bases provide hydroxide ions (OH–) and raise pH. The stronger the acid, the more readily it donates H+. For example, hydrochloric acid and lemon juice are very acidic and readily requite 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– chop-chop when placed in water, thereby raising the pH.
Most cells in our bodies operate within a very narrow window of the pH scale, typically ranging only from vii.2 to 7.half-dozen. If the pH of the torso is exterior of this range, the respiratory organization malfunctions, equally do other organs in the body. Cells no longer role properly, and proteins will break down. Deviation outside of the pH range can induce coma or even crusade expiry.
And then how is it that nosotros tin can ingest or inhale acidic or basic substances and not die? Buffers are the cardinal. Buffers readily absorb backlog H+ or OH–, keeping the pH of the body carefully maintained in the aforementioned narrow range. Carbon dioxide is part of a prominent buffer organization in the human body; it keeps the pH within the proper range. This buffer organisation involves carbonic acid (H2CO3) and bicarbonate (HCO3 –) anion. If too much H+ enters the body, bicarbonate will combine with the H+ to create carbonic acid and limit the decrease in pH. Likewise, if too much OH– is introduced into the organization, carbonic acrid will rapidly dissociate into bicarbonate and H+ ions. The H+ ions can combine with the OH– ions, limiting the increase in pH. While carbonic acrid is an of import product in this reaction, its presence is fleeting because the carbonic acid is released from the body as carbon dioxide gas each time we breathe. Without this buffer organisation, the pH in our bodies would fluctuate as well much and nosotros would fail to survive.
Department Summary
Water has many backdrop 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 first-class solvent. The hydrogen bonds between water molecules give water the ability to hold heat better than many other substances. As the temperature rises, the hydrogen bonds between water continually interruption 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 low pH value. A solution with a high number of hydroxide ions is bones and has a high pH value. The pH scale ranges from 0 to 14, with a pH of 7 being 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 conditions.
acid: a substance that donates hydrogen ions and therefore lowers pH
adhesion: the attraction between h2o molecules and molecules of a different substance
base of operations: a substance that absorbs hydrogen ions and therefore raises pH
buffer: a solution that resists a modify in pH past absorbing or releasing hydrogen or hydroxide ions
cohesion: the intermolecular forces between water molecules acquired past the polar nature of h2o; creates surface tension
evaporation: the release of water molecules from liquid water to form water vapor
hydrophilic: describes a substance that dissolves in water; h2o-loving
hydrophobic: describes a substance that does non dissolve in water; h2o-fearing
litmus newspaper: filter paper that has been treated with a natural water-soluble dye and so it can be 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
solvent: a substance capable of dissolving another substance
surface tension: the cohesive strength at the surface of a torso of liquid that prevents the molecules from separating
temperature: a measure of molecular motion
References
Humphrey, West., Dalke, A. and Schulten, K., "VMD—Visual Molecular Dynamics", J. Molec. Graphics, 1996, vol. 14, pp. 33-38. http://www.ks.uiuc.edu/Inquiry/vmd/
Media Attribution
- Figure two.7 by Gautam Dogra
- Figure 2.viii
- ice lattice by Jane Whitney
- (b) by Carlos Ponte
- Figure ii.x by Cory Zanker
- Figure ii.xi by Edward Stevens
Source: https://opentextbc.ca/biology/chapter/2-2-water/
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