2.2 - Water Flashcards
Explain the Water Molecule
Water is made up of 2 hydrogen atoms covalently bonded to one oxygen atm.
The electrons in the covalent bond are not shared equally.
Oxygen has a greater pull on the electrons shared with the hydrogens
The shared electrons spend more time at the oxygen atom than at the hydrogen atoms
Oxygen gains a partial negative charge and the hydrogens gain a partial positive charge
Hydrogen Bonds
The charge difference across the molecule (dipole)
allows water to form weak associations with other molecules
The slightly negative pole of water will attract positive charges
of other molecules and the slightly positive pole of water will
attract the negative charges of other molecules
When the slightly positive charges of a hydrogen atom are attracted to the slightly negative charges of a fluorine, oxygen or nitrogen in another molecule, it forms a hydrogen bond.
Hydrogen bonds are relatively strong due the high electronegativity of F, O and N.
Hydrogen bonds are the attraction between polar molecules
What are the 4 properties of water?
cohesion - binding together of two molecules of the same type (ex. two water molecules)
thermal - High specific heat capacity & High latent heat of vaporization
adhesion - Hydrogen bonds can form between water and other polar molecules, causing water to stick to them
solvent
Cohesion with Example
Hydrogen bonds cause water molecules to stay close/stick to each other and the hydrogen bonds hold the substance together
water molecules are linked by multiple hydrogen bonds,
in which the arrangement of the molecules is constantly changing
Ex. Transpiration - water molecules form a column through the
xylem at low pressure in which the molecules stick together by hydrogen bonds
Adhesion with Examples
This property occurs as a result of the polarity of a water molecule and its ability to form hydrogen bonds
Water molecules tend to stick to other molecules that are charged or polar causing water to stick to them
Ex. Useful in transpiration: adhesion of water to cellulose molecules in cell walls by hydrogen bonds helps counter the downward pull of gravity
If water evaporates from the cell walls and is lost from the leaf via the network of air spaces, adhesive forces cause water to be drawn out of the nearest xylem vessel. This keeps the walls moist so they can absorb carbon dioxide needed for photosynthesis.
Thermal Properties
High Specific heat capacity: the amount of heat needed for 1g of a substance to change its temperature by 1oC
Hydrogen bonds restrict the motion of water molecules and increases in the temperature of water require hydrogen bonds to be broken
High Heat of Vaporization: the quantity of heat a liquid must absorb for
1g to be converted to the gaseous state
The heat needed to turn a liquid molecule into a vapor molecule is known as latent heat of vaporization. Evaporation therefore has a cooling effect.
Solvent Properties
Its partially negative oxygen pole is attracted to positively charged ions and its partially positive hydrogen pole is attracted to negatively charged ions, so both dissolve.
Allows a large number of substances to dissolve within it (the universal solvent)
Ex. Cytoplasm is a complex mixture of dissolved substances in which the chemical reactions of metabolism occur.
Ex. Ions dissolved in the water component of blood most biochemical reactions occur in aqueous solutions
Hydrophilic
Water Loving
All substances that dissolve in water are hydrophilic, including polar molecules such as glucose, and particles with negative or positive charges such as chloride and sodium ions.
Substances that water adheres to are also hydrophilic e.g. cellulose
Hydrophobic
Water Fearing
The forces that cause nonpolar molecules to join together into groups in water
Molecules are hydrophobic if they do not have negative or positive charges and are non-polar
Insoluble in water, but soluble in solvents such as propanone
(acetone)
Ex. lipids found in cell membranes are hydrophobic
they will interact with each other and not the with the water
useful for forming a barrier
Water Vs. Methane
Formula : CH4 and H20
MM : 16 and 18
Density : 0.46 and 1 g per cm3
SHC : 2.2 and 4.2 J per g per C
LHoV : 760 and 2257 J/g
MP : -182 and 0 C
BP : -160 and 100 C
How does Water work as a Coolant in Sweat?
When the water evaporates from the surface of the skin, it takes heat with it.
With the loss of heat energy, the skin feels cool because water has a high latent heat of vaporization.
Sweat secreted from sweat glands is carried out from narrow ducts reaching to the surface
Sweat secretion is controlled by the hypothalamus of the brain
Other methods of cooling - when adrenaline is secreted we sweat even if we are already cold. This is because adrenaline is secreted when our brain anticipates a period of intense activity that will tend to cause the body to overheat.
Solutes in the sweat, especially ions such as sodium, are left on the skin surface and can sometimes be detected by their salty taste.
Transport of Materials in the Blood
Transport of essential molecules in the blood will depend on their solubility. Water soluble substances will travel freely in the blood, while water insoluble substances cannot
Water Soluble Substances
Sodium chloride: ionic compound that dissolves as ions which can be carried in the blood plasma
Amino Acids: have both amine groups and carboxyl groups and can be carried in the blood plasma. They have both neg and pos charges and therefore are soluble in water but their solubility varies depending on the R group, some of which are hydrophilic while others are hydrophobic. All amino acids are soluble enough to be carried dissolved in blood plasma.
Glucose: a carbohydrate and polar molecule containing many hydroxyl groups, so it can dissolve in water and be transported in blood plasma
Oxygen: small non-polar molecule that can dissolve in blood plasma in small amounts, but is mostly transported in red blood cells by the molecule hemoglobin.
As the temperature of water rises, the solubility of oxygen decreases, so blood plasma at 37 °C can hold much less dissolved oxygen than water at 20 °C or lower.
The amount of oxygen that blood plasma can transport around the body is far too little (low concentrations) to provide for aerobic cell respiration. This problem is overcome by the use of hemoglobin in red blood cells. Hemoglobin has binding sites for oxygen and greatly increases the capacity of the blood for oxygen transport.
Water Insoluble Substances
Fat molecules: non-polar and must be carried inside a lipoprotein composed of a single layer of phospholipids outside and fats inside. The hydrophilic phosphate heads of the phospholipids face outwards and are in contact with water in the blood plasma. The hydrophobic hydrocarbon tails face inwards and are in contact with the fats. There are also proteins in the phospholipid monolayer, hence the name lipoprotein.
Cholesterol: the large hydrophobic region of the molecule makes
it insoluble in water and must be transported in lipoprotein complexes
They only have a small hydrophilic region at one end and this is not enough to make cholesterol dissolve in water and instead it is transported with fats in lipoprotein complexes.
The cholesterol molecules are positioned in the phospholipid monolayers, with the hydrophilic region facing outwards in the region with the phosphate heads of the phospholipids.
