2.2 Water Flashcards
What is water made up of?
Two hydrogen atoms covalently bonded to an oxygen atom
What does covalent bonding involve with electrons?
The sharing of electrons
What is different in water molecules that does not match a typical covalent bonding property?
Electrons are not equally shared between the atoms
Which element in water attracts electrons more strongly and why?
Oxygen due to having a higher electronegativity
What causes polarity in water molecules?
The shared electrons orbit closer to the oxygen atom than the hydrogen atoms
Why is water described as being polar?
As it has a slight charge difference across the different poles of the molecule
What is the charge of oxygen atoms?
Slightly negative
What is the charge of hydrogen atoms?
Slightly positive
What allows water to form weak associations with other polar molecules?
The charge difference across the molecule
What will the slightly negative poles attract?
The slightly positive poles of other molecules
What does a hydrogen atom form when it is attached to fluorine, oxygen or nitrogen of another molecule?
A hydrogen bond
Why are hydrogen bonds relatively stronger than other polar associations?
Due to the high electronegativity of Fluorine, Oxygen and nitrogen
What does the dipolarity of a water molecule enable?
To form polar associations with other charged molecules
What bond can water form with other water molecules?
Hydrogen bonds
What are the three distinct properties of water?
Thermal properties
Cohesive/adhesive properties
Solvent properties
What gives water distinct properties not seen in other substances?
The intermolecular bonding between water molecules
Explain the thermal property of water?
Water can absorb much heat before changing state
What does water changing state require?
The breaking of hydrogen bonds and that needs the absorption of energy
Explain cohesive/adhesive properties of water?
Water will stick to other water molecules and charged molecules
What is cohesion?
When like molecules sticks together
What is adhesion?
When dissimilar molecules stick together
Explain solvent properties of water?
Water dissolves polar and ionic substances
What does water form to draw materials apart?
Competing polar associations
Why can water absorb significant amounts of heat before changing state?
Due to the hydrogen bonding between water molecules
Why is water an excellent medium for living organisms?
It is relatively slow to change temperature and thus supports the maintenance of constant conditions
Why does methane provide a good basis of comparison of water?
Due to the similarities in their structures
What does methane and water have in common?
Comparable size and weight
Comparable valence structures
Where do the differences in thermal properties between water and methane come from?
Differences in polarity between the molecules
Is methane polar or non polar?
Non polar
What type of bonds can methane form between its molecules?
Weak dispersion forces
What absorbs more heat before changing heat: methane or water?
Water
Does methane or water have a higher melting and boiling point?
Water
Does methane or water have a higher specific heat capacity?
Water
Does methane or water have a higher heat of vaporisation?
Water
Does methane of water have a higher heat of fusion?
Water
What is a mechanism used by humans to cool down?
The evaporation of water as sweat
What does evaporation require?
An input of energy
Where does the energy needed for evaporation for sweat come from?
The surface of the the skin when it is hot
What happens to the skin when sweat evaporates?
It cools
Because water is polar it will be attracted to other molecules that are…
Polar or have an iconic charge
Why does water absorb a lot of thermal energy before it evaporates?
Because it has a high specific heat capacity
What will water form with polar and charged molecules?
Intermolecular associations
What explains waters surface tension?
Its cohesive properties
What does hydrogen bonding between water molecules allow?
The liquid to resist low levels of external force
What allows water to flow in opposition to gravity?
Attraction to charged or polar surfaces
What explains waters capillary action?
Its adhesive properties
What makes water suitable for smaller organisms to move along its surface?
Its high surface tension which makes it sufficiently dense
Why is capillary action necessary?
To allow water to be transported up plant stems via a transpiration stream
Why is water often referred to as the universal solvent?
Due to its capability to dissolve a large number of substances
What can water dissolve?
Any substance that contains charged particles or electronegative atoms
Why can water dissolve substances?
Because the polar attraction of the large amounts of water molecules can weaken intramolecular forces which causes the dissociation of the atoms
What forms dispersive hydration shells?
The slightly charged regions of the water molecule surround atoms of opposing charge
What are hydrophilic substances?
Substances that freely associate and readily dissolve in water
What are examples of hydrophilic substances?
All polar molecules and ions
What are hydrophobic substances?
Substances that do not freely associate or dissolve in water
What are examples of hydrophobic substances?
Large, non polar molecules
What does the transport of essential molecules within the bloodstream depend on?
Their solubility in water
What is the difference in water soluble and water insoluble substances when they travel in the blood plasma?
Water soluble substances can move freely but water insoluble substances cannot
What are four water soluble substances?
Sodium chloride
Oxygen
Glucose
Amino acids
Why can sodium chloride transport freely in blood?
It is an ionic compound
Is oxygen soluble?
Yes but in low amounts
How does most oxygen travel in the blood?
By haemoglobin within red blood cells
Why can glucose travel freely in blood?
As it has many hydroxyl groups which can associate with water
What state must amino acids be in for them to be transported in the blood?
An ionized state
Why won’t lipid dissolve in water?
Because they are non polar and hydrophobic
How do lipids move through the bloodstream?
By forming complexes with proteins called lipoproteins
What direction does the hydrophilic portions of proteins, cholesterol and phospholipids face and why?
Outwards to shield the the internal hydrophobic components
