2.2 Syllabus
U1. Water molecules are polar and hydrogen bonds form between them.
-Water is made up of two hydrogen atoms covalently bonded to an oxygen atom (molecular formula = H2O)
-While this covalent bonding involves the unequal sharing of electrons, they are not shared equally between the atoms.
-Water is described as being polar because it has a slight charge difference across the different poles of the molecule
-While this covalent bonding involves the unequal sharing of electrons, they are not shared equally between the atoms.
-Water is described as being polar because it has a slight charge difference across the different poles of the molecule
- The oxygen atom is slightly negative (δ–) while the hydrogen atoms are slightly positive (δ+). Because of H2O molecules are bent rather than linear, 2 hydrogen atoms are on same side of molecule and form 1 pole and oxygen forms the opposite pole
- Positive particles and negatively charged particles attract each other and form an ionic bond
- Partial charges → Attraction less
U2. Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.
-The dipolarity of a water molecule enables it to form polar associations with other charged molecules (polar or ionic)
1. Thermal Properties: Water can absorb much heat before changing state (requires breaking of hydrogen bonds).
→ So amount of energy needed to raise the temp of water is relatively large.
→Water’s temp remains relatively stable in comparison to air or land so thermally stable habitat for aquatic organisms.
→This makes it god evaporative coolant. Sweating -> Example of use of water as coolant.
2. Cohesive Properties (Surface tension)
→It refers to binding together of 2 molecules of same type for instance two water molecules. They stick to each other due to H bonding. The hydrogen bonding between water molecules allows the liquid to resist low levels of external force (surface tension)
→It’s useful for H2O transport in plants.
→Due to H bonding this rarely happens and water can be pulled up to top of tallest trees – over 100m.
3. Adhesive Properties (Capillary Action)
→H bonds can form between water and other polar molecules, causing water to stick to them = adhesion.
→Property is useful in leaves where H2O adheres to cellulose molecules in cell walls.
→This capillary action is necessary to allow water to be transported up plant stems via a transpiration stream
4. Solvent Properties:
→ Water dissolves polar and ionic substances
→Its partially negative oxygen pole is attracted to negatively charged ions, so both dissolve.
Related Question:
Q. Properties of Water
Answer:
Good solvent: Due to polarity of water molecules and many different substances dissolve in it
Cohesion: Cohesion between adjacent water molecule due to hydrogen bonds
Heat: Large amount of energy needed to change temperature and energy needed to break H bonds
Cooling: High heat of vaporization and heat used it break H bonds so H2O can change to gas
Great Density at 4 celsius degree: Allows ice to form on top of water
1. Thermal Properties: Water can absorb much heat before changing state (requires breaking of hydrogen bonds).
- High specific heat capacity:
→ So amount of energy needed to raise the temp of water is relatively large.
→Water’s temp remains relatively stable in comparison to air or land so thermally stable habitat for aquatic organisms.
- High latent heat of vaporization:
→This makes it god evaporative coolant. Sweating -> Example of use of water as coolant.
2. Cohesive Properties (Surface tension)
→It refers to binding together of 2 molecules of same type for instance two water molecules. They stick to each other due to H bonding. The hydrogen bonding between water molecules allows the liquid to resist low levels of external force (surface tension)
→It’s useful for H2O transport in plants.
→Due to H bonding this rarely happens and water can be pulled up to top of tallest trees – over 100m.
3. Adhesive Properties (Capillary Action)
→H bonds can form between water and other polar molecules, causing water to stick to them = adhesion.
→Property is useful in leaves where H2O adheres to cellulose molecules in cell walls.
→This capillary action is necessary to allow water to be transported up plant stems via a transpiration stream
4. Solvent Properties:
→ Water dissolves polar and ionic substances
→Its partially negative oxygen pole is attracted to negatively charged ions, so both dissolve.
Related Question:
Q. Properties of Water
Answer:
Good solvent: Due to polarity of water molecules and many different substances dissolve in it
Cohesion: Cohesion between adjacent water molecule due to hydrogen bonds
Heat: Large amount of energy needed to change temperature and energy needed to break H bonds
Cooling: High heat of vaporization and heat used it break H bonds so H2O can change to gas
Great Density at 4 celsius degree: Allows ice to form on top of water
U3. Substances can be hydrophilic or hydrophobic.
-Substances that freely associate and readily dissolve in water are characterized as hydrophilic (‘water loving’) -> Chemically attracted to water
- Hydrophilic substances include all polar molecules and ions. All substances that dissolve in H2O are hydrophilic, including polar molecules
- Hydrophobic substances include large, non-polar molecules (such as fats and oils)
A1. Comparison of the thermal properties of water with those of methane.
A2. Use of water as a coolant in sweat.
-Sweat is secreted by glands in skin and it is carried along narrow ducts to the surface of the skin where it spreads out. Heat needed for evaporation of water in sweat is taken from the tissues of the skin, reducing their temp. So blood flowing through the skin is cooled.
→Effective method of cooling body because water has high latent heat of vaporization.
-Controlled by hypothalamus of brain. Has receptors that monitor blood temp and also receives sensory inputs from temp receptors in the skin.
-The evaporation of water as sweat is a fundamental mechanism employed by humans as a means of cooling down
→Effective method of cooling body because water has high latent heat of vaporization.
-Controlled by hypothalamus of brain. Has receptors that monitor blood temp and also receives sensory inputs from temp receptors in the skin.
-The evaporation of water as sweat is a fundamental mechanism employed by humans as a means of cooling down
A3. Modes of transport of glucose, amino acids, cholesterol, fats. Oxygen, and sodium in blood in relations to their solubility in water.
-The transport of essential molecules within the bloodstream will depend on their solubility in water
- Water soluble substances will usually be able to travel freely in the blood plasma, whereas water insoluble substances cannot
- Sodium chloride (NaCl) is an ionic compound and its components (Na+ and Cl–) may be freely transported within the blood
- Oxygen is soluble in water but in low amounts
- Lipids (fats and cholesterol) are non-polar and hydrophobic and hence will not dissolve in water