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.
Difference between specific heat capacity and latent heat of vaporisation.
-The specific heat capacity is the amount of energy needed to heat up one gram of water by one degree Celsius.
-The latent heat of vaporisation is the amount of energy needed to change water liquid into water vapour (gas).
Solvent properties of water
-Water is one of the best-known solvents, considered the universal solvent. It can dissolve ionic compounds as well as many polar compounds such as glucose.
-All reactions in cells occur in a liquid medium and are dependent on water to dissolve the reactants for reactions to proceed (e.g. hydrolysis).
-Water dissolves many substances that are later carried around the body in the blood plasma.
-These are water-soluble metabolites such as glucose, amino acids, and sodium chloride.
-However, not every substance can be dissolved in water. These are known as fat-soluble or water-insoluble substances.
How do water molecules dissolve a compound (solute)?
The positive and negative ions of the solute interact with the δ+ (positive) and δ- (negative) dipoles of the water molecules.
Diagram showing how water molecules (solvent) act dissolve a compound (solute)
Benefit to living organisms of cohesive properties of water
1) Allows water to be pulled up from the roots to the leaves of plants.
2) Permits insects, such as pond skaters, to walk/float on the surface of water to catch their prey.
Benefit to living organisms of adhesive properties of water
1) Capillary action generated by adhesive forces assists the pumping action of the heart to help blood move through blood vessels.
2) Adhesion of water molecules to the cell wall of xylem vessels helps water move against gravity from the roots to the leaves.
Benefit to living organisms of thermal properties of water
1) Evaporation of sweat from body surfaces involves heat loss, which brings about a cooling effect.
2) The high specific heat capacity of water makes aquatic ecosystems more stable than terrestrial.
Benefit to living organisms of solvent properties of water
1) Water dissolves mineral ions in the soil and transports them along xylem vessels from the roots to all parts of the plant.
2) Water in blood plasma dissolves a range of solutes and gases, which makes it possible for blood to transport nutrients and gases around the body
All ___ contain water
Living organisms
Water molecules form ___ with each other
Hydrogen bonds
What causes water to have a relatively high specific heat capacity?
Hydrogen bonds between hydrogen and oxygen of different water molecules.
What property of water makes it an excellent coolant?
Water molecules are dipolar, allowing strong cohesive forces between the molecules.
Why is it necessary to transport many compounds throughout the body of a multicellular organism such as a human?
-Each cell needs access to oxygen, glucose, and minerals.
-At the same time, waste products have to be excreted.
-As a water-based liquid, blood takes care of the majority of these tasks.
-So, if a compound dissolves easily in water, it can usually be transported by blood.
-These compounds are transported in the blood plasma.
-The water-insoluble substances will be absorbed and transported via lymph vessels.
What biological molecules are found in blood?
-Glucose
-Amino acids
-Fats
-Cholesterol
-Oxygen
-Sodium chloride
Relationship between glucose and blood
-As a polar molecule, glucose is soluble in water so it can be transported in the blood.
-Blood glucose concentration needs to be strictly maintained between certain levels because of its effect on osmotic potential.
Relationship between amino acids and blood
-These are both negatively and positively charged.
-Most of them are soluble in water.
-However, their solubility varies depending on their size and the R group.
-Amino acids with a hydrophilic R group will be easily dissolved in water and transported in the blood.
-If amino acids contain a hydrophobic R group, they will not be easily dissolved in water and will be transported in lower concentrations in the blood.
Relationship between fats and blood
As they are nonpolar, fats are generally insoluble in water and therefore are transported in structures called lipoproteins (a single layer of phospholipids with proteins embedded among the molecules surrounding the fat).
Relationship between cholesterol and blood
-Cholesterol is required for the synthesis of many biologically important molecules and is a component of membranes.
-It requires the help of transport lipoproteins to be transported in blood because it is hydrophobic.
Relationship between oxygen and blood
-Oxygen is nonpolar but due to its small size, it is soluble in water to a limited extent.
-This is why oxygen transported in the blood is bound to the protein called hemoglobin.
Relationship between sodium chloride and blood
-As an ionic compound, sodium chloride is transported in blood in the form of Na + and Cl - ions .
-These ions are easily dissolved in water.
Diagram showing what nutrients and gases blood plasma carries
Which materials are dissolved in the blood?
Amino acids, sodium chloride and carbon dioxide.
Which materials are dissolved in the blood?
Amino acids, sodium chloride and carbon dioxide.
Water and ___ are both covalent compounds as they are made of atoms sharing electrons in covalent bonds.
Methane
Structure of water vs. methane
-Water consists of two hydrogen atoms attached to one oxygen atom, while methane has one carbon atom bonded to four hydrogen atoms.
-They are both small in size and have a similar molecular mass.
-However, they have very different properties, mainly because water is a polar molecule and methane is a non-polar molecule.
The cohesive, adhesive, thermal and solvent properties of water are all related to its ___
Polar nature and presence of hydrogen bonds.
Diagram showing the structure of a methane molecule
What is methane?
A gas that is produced by anaerobic bacteria as a waste product. It is also a greenhouse gas.
Comparison between physical state of water and methane at 20°C
Water = liquid
Methane = gas
Comparison of the polarity of water and methane
Water = polar
Methane = non-polar
Comparison of the solvent properties of water and methane
Water = excellent solvent
Methane = not a solvent
Comparison between boiling temperature of water and methane
Water = 100°C
Methane = -161 °C
Comparison between melting point of water and methane
Water = 0°C
Methane = -182°C
Comparison between specific heat capacity (energy in joules needed to change the temperature of unit mass of a substance by 1°C) of water and methane
Water = 4.2 J/g/°C
Methane = 2.2 J/g/°C
Comparison between latent heat of vaporisation (energy needed to convert a substance from liquid to vapour phase) of water and methane
Water = 2257 J/g
Methane = 760 J/g
Examples of sources of methane
-Wetlands
-Biomass burning
-Landfills
The latent heats of vaporisation of methane and water are 760 J/g and 2257 J/g, respectively. This implies that ___
Less energy is required to evaporate methane.
Which greenhouse gas has a chemical formula of CH4?
Methane
Organisms can live on ice sheets because ice is ___
Less dense than water
Table showing how different substances are transported in the blood based on their solubility in water
