1.7 & 1.8 Water and Inorganic ions Flashcards
What is the structure of water?
- 2 atoms of hydrogen covalently bonded to a molecule of oxygen
- Polar molecule - electrons not evenly distributed across the molecule (hydrogens slightly positive, oxygens slightly negative)
- attraction between these charges forms hydrogen bond between water molecules
How does the structure of water affect its properties? x5
- high heat capacity
- large latent heat of vaporisation
- strong cohesion between water molecules
- an important solvent
- a metabolite in many metabolic reactions
What is specific heat capacity?
The heat needed to raise the temperature of 1kg of water by 1°C
What does having a high specific heat capacity mean for water?
It can absorb large amounts of heat energy before its temperature raises a significant amount
What is evaporation?
In a body of water some molecules of water are moving at faster speeds (have higher kinetic energy). Some have enough kinetic energy to escape the water, moving into the air.
What happens when the fast moving molecules of water evaporate?
Their energy goes with them, leading to the average kinetic energy of the water to decrease. This means the water cools down. The energy that is lost is called the latent heat of vaporisation
Why is there a strong cohesion between water molecules?
- Due to their polarity (charges), water molecules are attracted to each other, and form hydrogen bonds
- These hydrogen bonds help hold water together, so they can flow as a continuous stream
- This is known as mass flow
What is a solvent?
A solvent is a liquid that other substances (called solutes) can dissolve
Why is water an important solvent?
When substances are dissolved in water they are free to move around and react with other molecules
Why is high heat capacity important to living organisms?
*buffers changes in temperature
- The bodies of living organisms are mostly made of water. This water in and around our cells absorbs a lot of heat energy without its temperature increasing much. The water ‘buffers’ the heat changes
- Also an advantage for aquatic organisms as large bodies of water, like seas or lakes, do not change temperature as quickly as terrestrial environments
Why is large latent heat of vaporisation important to living organisms?
*so provides a cooling effect through evaporation
- Animals that are able to sweat can keep cool as the water in sweat evaporates off the surface of the animal
- Plants are also cooled when water evaporates from their leaves
Why is strong cohesion between water molecules important for living organisms?
- so supports columns of water in plants/so produces surface tension supporting small organisms
- In plants, water moves up the xylem vessels as a continuous stream. This allows water to move from the roots to the top of the tallest trees
- Water cohesion leads to ‘surface tension’ making water behave as if there is a skin where the water meets air. This allows small animals to live on the surface of water bodies
Why is water being an important solvent important to living organisms?
*so metabolic reactions can occur/allowing transport of substances
- The metabolic reactions that happen inside all living organisms can only happen when the reactants are dissolved in water
- Substances being dissolved in water also allows them to be transported around the bodies of living organisms
Why is water being a metabolite in many metabolic reactions important to living organisms?
*a metabolite in condensation/hydrolysis/photosynthesis/respiration
- Hydrolysis reactions are important in digestion of large molecules in animals
- Condensation reactions are important in synthesis of important molecules such as proteins in living organisms
Why is water a polar molecule?
O is more electronegative than H, so attracts the electron density in the covalent bond more strongly
