2.2 Water Flashcards
Structure of water
Two hydrogen atoms and one oxygen atom joined by covalent bonds.
Charge of water
-The oxygen atom is more electronegative than the hydrogen atoms.
-This means that oxygen has a greater pull on the electron cloud that exists between the atoms.
-Therefore, oxygen acquires a slightly negative charge (δ-), leaving each hydrogen atom with a slightly positive charge (δ+).
-The polarity of water is the main reason for its important biological properties such as solvency, cohesion, and adhesion.
The symbol delta δ is used to denote ___
Partial changes in charge
Diagram of a water molecule
Why are water molecules polar?
-Due to their dual nature.
-They have both positive and negative charges and act like small magnets.
What does the polarity of water molecules allow?
-The formation of hydrogen bonds between water molecules: the partially positive hydrogen atoms of one molecule are attracted to the partially negative oxygen atoms of other water molecules.
-This means that most polar or charged compounds can be dissolved in water.
-Such compounds are said to be hydrophilic.
Diagram showing polar water molecules joined together by hydrogen bonds.
What are hydrogen bonds?
-Weak interactions between water molecules
-These are responsible for many important properties of water such as cohesion and adhesion.
Examples of hydrophilic compounds
Sugars and most salts
Diagram of glucose
Diagram of fructose
Glucose and fructose are both ___
Hydrophilic and can be dissolved in water.
What kind of substances are fats and oils?
-Non-polar substances.
-There is no attraction between them and water molecules; instead they repel each other.
-You can’t mix water and oil because oil is hydrophobic.
Example of a hydrophobic property in nature.
-Some leaves have a waxy cuticle that has strong hydrophobic properties.
-It causes water to form droplets to minimize contact between the leaf and the water.
A hydrophilic substance is one that ___
Is soluble in water.
What types of compounds can be dissolved in water?
Polar compounds
What properties does the polarity or dipolarity of water explain?
1) Cohesion
2) Adhesion
3) Thermal properties
4) Solvent properties
Cohesion of water
-This is the tendency of water molecules to stick to each other due to the hydrogen bonding between them.
-Each water molecule can potentially form four hydrogen bonds with other water molecules in a tetrahedral arrangement.
Explain the high surface tension of water (cohesion)
-Although hydrogen bonds are weak bonds, the presence of a large number of hydrogen bonds in water gives the cohesive forces great strength.
-This, in turn, is responsible for the high surface tension of water, i.e. the stickiness, due to hydrogen bonding, of water molecules makes the water surface behave as a strong elastic membrane, allowing small organisms or some objects that are denser than water, to float on the water surface.
-Surface tension is also responsible for water droplets adopting a spherical shape, minimizing the ratio of area to volume.
Adhesion of water
-This is the interaction that water molecules have with other (different) molecules (e.g. a glass surface) and explains why water molecules stick to other polar compounds by forming hydrogen bonds.
-Forces of adhesion are responsible for capillary action, which is defined as the movement of water molecules and all the things that are dissolved in it within thin spaces without relying on gravity.
-This property of water molecules is essential to allow water to be transported up the stems of plants.
Diagram of how capillary action caused by the adhesive properties of water
Define cohesion and adhesion (how are they different)?
-Cohesion and adhesion describe different properties of water molecules.
-Cohesion is the interaction among water molecules, while adhesion is the interaction between water molecules and a surrounding material or surface.
Diagram showing the difference between adhesion and cohesion
.
Thermal properties of water
-The hydrogen bonds that hold water molecules together are responsible for the unique thermal properties of water including the high specific heat capacity.
-In order to break down the hydrogen bonds in water, a high amount of energy is needed.
-The high specific heat capacity of water means that the temperature in aquatic ecosystems, for example, ponds, lakes, and seas, does not change rapidly, making these ecosystems stable.
Define specific heat capacity
The amount of heat that must be absorbed or released for 1g of a substance to change its temperature by 1°C.
Why is water a great coolant?
-Because a large amount of energy is needed to turn liquid water into water vapor.
-This means that water has a high latent heat of vaporization, which can be defined as the amount of heat 1 g of a liquid absorbs to change its state from liquid to gaseous.
-When the water in sweat evaporates on the surface of our skin, it cools down its surface by taking away energy in the form of heat.
-If we compare water to any other substance, it has a high heat of vaporization.
-Related to the high heat of vaporization is the boiling point.
Diagram showing how water molecules (solvent) act dissolve a compound (solute)
Diagram showing what nutrients and gases blood plasma carries
Diagram showing the structure of a methane molecule
Table showing how different substances are transported in the blood based on their solubility in water
