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Properties of Water

Grades 9-10 | Argumentative | Source-Based

Source Lexile®: 1160L-1170L

Learning Standards

 

 

 

Prompt:  Today you will read two passages and examine an additional graphic about water. Write an argumentative essay in which you make a claim about which is the most important property of water. Be sure to include an overview of all three properties of water and a description of how each property relates to the structure of water. Cite evidence and examples from the passages and the graphic to support your claim.

 

 

 

Source 1

Excerpt from A Short History of Nearly Everything

by Bill Bryson

 

  1. Imagine trying to live in a world dominated by dihydrogen oxide, a compound that has no taste or smell and is so variable in its properties that it is generally benign but at other times swiftly lethal. Depending on its state, it can scald you or freeze you. In the presence of certain organic molecules it can form carbonic acids so nasty that they can strip the leaves from trees and eat the faces off statuary. In bulk, when agitated, it can strike with a fury that no human edifice could withstand. Even for those who have learned to live with it, it is an often murderous substance. We call it water.
     
  2. Water is everywhere. A potato is 80 percent water, a cow 74 percent, a bacterium 75 percent. A tomato, at 95 percent, is little but water. Even humans are 65 percent water, making us more liquid than solid by a margin of almost two to one. Water is strange stuff. It is formless and transparent, and yet we long to be beside it. It has no taste and yet we love the taste of it. We will travel great distances and pay small fortunes to see it in sunshine. And even though we know it is dangerous and drowns tens of thousands of people every year, we can't wait to frolic in it.
     
  3. Because water is so ubiquitous we tend to overlook what an extraordinary substance it is. Almost nothing can be used to make reliable predictions about the properties of other liquids and vice versa. If you knew nothing of water and based your assumptions on the behavior of compounds most chemically akin to it-hydrogen selenide or hydrogen sulphide notably--you would expect it to boil at minus 135 degrees Fahrenheit and to be a gas at room temperature.
     
  4. Most liquids when chilled contract by about 10 percent. Water does too, but only down to a point. Once it is within whispering distance of freezing, it begins--perversely, beguilingly, extremely improbably--to expand. By the time it is solid, it is almost a tenth more voluminous than it was before. Because it expands, ice floats on water-" an utterly bizarre property," according to John Gribbin. If it lacked this splendid waywardness, ice would sink, and lakes and oceans would freeze from the bottom up. Without surface ice to hold the heat in, the water's warmth would radiate away, leaving it even chillier and creating yet more ice. Soon even the oceans would freeze and almost certainly stay that way for a very long time, probably forever--hardly the conditions to nurture life. Thankfully for us, water seems unaware of the rules of chemistry or laws of physics.
     
  5. Everyone knows that water's chemical formula is H2O, which means that it consists of one largish oxygen atom with two smaller hydrogen atoms attached to it. The hydrogen atoms cling fiercely to their oxygen host, but also make casual bonds with other water molecules. The nature of a water molecule means it engages in a kind of dance with other water molecules, briefly pairing and then moving on, like the ever-changing partners in a quadrille1, to use Robert Kunzig's nice phrase. A glass of water may not appear very lively, but every molecule in it is changing partners billions of times a second. That's why water molecules stick together to form bodies like puddles and lakes, but not so tightly that they can't be easily separated as when, for instance, you dive into a pool of them. At any given moment only 15 percent of them are actually touching.
     
  6. In one sense the bond is very strong-it is why water molecules can flow uphill when siphoned and why water droplets on a car hood show such a singular determination to bead with their partners. It is also why water has surface tension. The molecules at the surface are attracted more powerfully to the like molecules beneath and beside them than to the air molecules above. This creates a sort of membrane strong enough to support insects and skipping stones. It is what gives the sting to a belly flop.
     
  7. I hardly need point out that we would be lost without it. Deprived of water, the human body rapidly falls apart. Within days, the lips vanish "as if amputated, the gums blacken, the nose withers to half its length, and the skin so contracts around the eyes as to prevent blinking." Water is so vital to us that it is easy to overlook that all but the smallest fraction of water on Earth is poisonous to us-deadly poisonous- because of the salt within it.
     
  8. We need salt to live, but only in small amounts, and seawater contains way more about seventy times more-salt than we can safely metabolize. A typical liter of seawater will contain only 2.5 teaspoons of common salt- the kind we sprinkle on food-but larger amounts of other elements, compounds, and other dissolved solids, which are collectively known as salts. The proportions of these salts and minerals in our tissues is uncannily similar to seawater--we sweat and cry seawater, as Margulis and Sagan have put it--but curiously we cannot tolerate them as an input. Take a lot of salt into your body and your metabolism very quickly goes into crisis. From every cell, water molecules rush off like so many volunteer firemen to try to dilute and carry off the sudden intake of salt. This leaves the cells dangerously short of the water they need to carry out their normal functions. They become, in a word, dehydrated. In extreme situations, dehydration will lead to seizures, unconsciousness, and brain damage. Meanwhile, the overworked blood cells carry the salt to the kidneys, which eventually become overwhelmed and shut down. Without functioning kidneys you die. That is why we don't drink seawater.
     
  9. There are 320 million cubic miles of water on Earth and that is all we're ever going to get. The system is closed: practically speaking, nothing can be added or subtracted. The water you drink has been around doing its job since the Earth was young. By 3.8 billion years ago, the oceans had (at least more or less) achieved their present volumes.
     
  10. The water realm is known as the hydrosphere and it is overwhelmingly oceanic. Ninety-seven percent of all water on Earth is in the seas, the greater part of it in the Pacific, which covers half the planet and is bigger than all the landmasses put together. Although the Pacific holds just over half of all the ocean water (51.6 percent to be precise); the Atlantic has 23.6 percent and the Indian Ocean 21.2 percent, leaving just 3.6 percent to be accounted for by all other seas. The average depth of the ocean is 2.4 miles, with the Pacific on average about a thousand feet deeper than the Atlantic and Indian Oceans. Altogether 60 percent of the planet's surface is ocean more than a mile deep. As Philip Ball notes, we would better call our planet not Earth but Water.
     
  11. Of the 3 percent of Earth's water that is fresh, most exists as ice sheets. Only the tiniest amount--0.036 percent--is found in lakes, rivers, and reservoirs, and an even smaller part--just 0.001 percent--exists in clouds or as vapor. Nearly 90 percent of the planet's ice is in Antarctica, and most of the rest is in Greenland. Go to the South Pole and you will be standing on nearly two miles of ice, at the North Pole just fifteen feet of it. Antarctica alone has six million cubic miles of ice- enough to raise the oceans by a height of two hundred feet if it all melted. But if all the water in the atmosphere fell as rain, evenly everywhere, the oceans would deepen by only an inch.

 

Source: Bryson, Bill (2003). A Short History of Nearly Everything, USA: Broadway Books.
 


  1. Quadrille - a square dance typically performed by four couples 
     

 

 

 

Source 2

The Distribution of Water on Earth

 

PropertiesofWater_Source2_Image1.png

 

 

 

Source 3

The Properties of Water

 

  1. Water (H2O) is fundamental to the existence of life as we know it. Indeed, it is so familiar to us that we take its properties for granted. What makes water so important? What is the relationship between water and other biomolecules? In order to answer these questions we need to take a close look at water and at some of the properties of its electrons, which have a profound influence on its character.
     
  2. As you probably learned in elementary school, a single molecule of water consists of two hydrogen atoms covalently bound to one oxygen atom. This arrangement does not sound very exciting; however, a closer examination of the bonds within the water molecule reveals something unique. Specifically, water is a polar molecule, meaning that it has different electrical properties on opposite ends; specifically, it has two partial positive charges in association with the two H-atoms, and two partial negative charges associated with the oxygen atom.

 

PropertiesofWater_Source3_Image1.png

alt_text Figure 1. The polar nature of a water molecule and hydrogen bonds between water molecules.

 

  1. To understand these properties, you need to know that not all covalent bonds (those bonds that involve the sharing of electrons) are equal. Specifically, oxygen is highly electronegative and tends to pull electrons close to it when forming covalent bonds with hydrogen. This creates an unequal distribution around each O-H bond; therefore, the hydrogen has a partial positive charge (and conversely, the oxygen has a slightly negative character). Importantly, the partial negative charges on one water molecule can interact with the partial positive charges on another water molecule to form a hydrogen bond (as shown in Figure 1 with dotted lines). Hydrogen bonds contribute to many of the unique features of water.


    PropertiesofWater_Source3_Image2.png


    Figure 2. Surface tension of water. A stonefly stands on water.

     

  2. The state in which liquid water molecules are stuck together, via hydrogen bonding, or H-bonding, gives water a physical property termed cohesion. Due to cohesion, water has a high surface tension (resistance to disruption at the surface). This property is exploited by many insects (e.g., the stonefly in Figure 2) and some vertebrates (e.g., basilisk lizards), which can actually stand or run on water without breaking the surface and falling through.
     

  3. Water is a repository for heat due to its high specific heat. This means that it takes a relatively large amount of energy to raise the temperature of water. Therefore, water absorbs (and stores) heat energy more efficiently than many other substances. Biologically, this is extremely important because large bodies of water tend to have relatively stable temperatures, whereas the air around them may fluctuate. The moderate temperatures in oceans and large lakes make them suitable year-round for an abundance of aquatic life. Water also has a relatively high heat of vaporization, therefore, water is relatively resistant to phase changes. (It takes a relatively large amount of energy to break all of the H-bonds in water to produce water vapor or steam.) This property allows some organisms to use water, in the form of sweat, to cool down.
     

  4. Water expands during freezing (Figure 3). When water molecules slow down and ice forms (below freezing), the hydrogen bonds keep water molecules at a distance from each other in a characteristic, 3-dimensional crystal that is relatively spacious. The distinction between ice and liquid water is illustrated in this figure, which also depicts how this arrangement makes ice less dense than water, thereby allowing ice to float on water.

     

PropertiesofWater_Source3_Image3.png


Figure 3. The structure of ice compared with the structure of water.

 

  1. Water is an excellent solvent, capable of dissolving many compounds. The polar character of water means that anything with a charge can dissolve in water. NaCl is table salt, and when added to water its sodium and chloride atoms disassociate. These ions have a charge. Both the positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-) can readily bond to the polar water molecules and in doing so they dissolve. Compounds that dissolve readily in water are hydrophilic. Compounds that do not interact with water are hydrophobic.
     

  2. In conclusion, water has many important properties that are important to life. The cells of terrestrial organisms (including ours) contain greater than 70% water, and most cells are surrounded by water. This means that a large percentage of biomolecules operate in an aqueous compartment. It should not surprise you to learn that water plays an important role in the functioning of biochemicals.

 

Source: Woodward, D. (2013, Jan.) Carbon and Life, Penn State Biology 110. Retrieved July 29, 2015 from https://wikispaces.psu.edu/displaylbio 110/Carbon-and-Life

 

 

 

 

Rubric:

PropertiesofWater_XP_Rubric_image_2017-09-25_Page_1.png

 

 

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