Water Flashcards
What type of bonding holds the hydrogen and oxygen molecules together?
Covalent bonds
What type of bonding holds water molecules together?
Hydrogen bonds
Explain how water is bonded (using electrons in your answer).
Each oxygen atom shares electrons with two hydrogen atoms. The oxygen atom has a greater affinity for for the electrons than the hydrogen’s so it pulls them closer (the electrons are not evenly distributed along the covalent bond). Making the O slightly negative (δ-) and the hydrogens slightly positive (δ+) which creates charged regions.
What is a water molecule?
A polar molecule (it has polarity - its dipolar)
Explain hydrogen bonding.
They are weak bonds between a slightly positively charged hydrogen atom and a slightly negatively charged atom in another molecule (in this case its oxygen). Hydrogen bonding gives water some of its useful properties. They provide water’s stable structure.
What is a solute?
The thing that dissolves.
What is a solvent?
A substance capable of dissolving another substance.
What is specific heat capacity (SHC)?
The amount of energy (heat) required to raise 1kg of water through 1 degree centigrade.
What is water’s (SHC) like?
High (4.2kJ) due to the H-bonds which helps keep the temperature of large bodies of water constant (most of the thermal energy absorbed is used to break hydrogen bonds and change state so less energy is available to inc. the temp.) - it can buffer (resist) changes in temperature.
What is Latent heat of Vaporisation?
The amount of energy required to change the state of 1 kg of a material without changing its temperature.
What is water’s latent heat of vaporisation like?
It is high. Water changes state when the hydrogen bonds holding water together are broken. This allows water molecules on the surface to escape into the air as a gas. It is especially difficult because hydrogen molecules continually attract other water molecules, continually making and breaking bonds.
What effect does water having a high latent heat of vaporisation have?
Large bodies of water can be cooled with minimal loss of water. Useful for living organisms as they can use water loss through evaporation (via sweating or panting in animals or the transpiration stream in plants) to cool down without loosing too much water - when water evaporates it carries heat energy away from a surface .
Why is water such a good solvent?
It has polarity so if the solute is an ionic compound the slightly positively charged end of the water molecule will be attracted to the negative ion and vice versa because opposites attract. Water molecules will surround the solute keeping the solute apart - its dissolved.
What does hydrophilic mean?
Will dissolve in water.
Examples of water being a good solvent?
Movement of minerals to lakes and seas, absorption of dissolved minerals, transport of dissolved substances (via the blood and lymph in animals), removal of metabolic waste such as urea and ammonia in urine, 70-95% of cytoplasm is water and that is where the basis on metabolic reactions occur.
What is cohesion?
The attraction between molecules of the same type (eg. two water molecules).
Is water cohesive?
Yes, very - due to the hydrogen bonds and therefore its polarity.
What properties does water have due to the fact its cohesive?
Helps water flow meaning its great for transporting substances, high surface tension when it comes into contact with air, makes long thin water columns very strong and difficult to break.
Examples of use of water because its cohesive?
Water being pulled up through the xylem in the transpiration stream due to the molecules sticking together (it can flow), surface tension which is the reason why sweat forms droplets form and why insects can walk on the surface of a pond.
What is adhesion?
When a substance (eg. water) can stick to other things
Why is water such a good lubricant?
Because its cohesive and adhesive which makes it viscous. Eg. synovial fluid (lubricates many vertebrae joints, pleural fluid (minimises friction between lungs and thoracic cage - ribs - during breathing), mucus (permits easy passage of faeces down the colon and lubricates the penis and vagina during intercourse).
Give info about waters molecular mobility.
Constant making and breaking of H-bonds because they are so weak which allows osmosis to take place.
What is waters transparency like?
Is transparent (lets light through) and has high transmission, so photosynthesis is possible in shallow areas.
Give info about waters density as it freezes.
When it cools its density increases until it gets to 4 degrees then it decreases as the water molecules move further apart to provide space for all four H-bonds to fit (it expands) this makes ice float on water, the max no. of hydrogen bonds are formed as it reaches freezing point
