2.2 Properties of Water Flashcards
What is water made up of ?
Two hydrogen covalently bonded to oxygen
Why is water polar ?
Electrons are not shared equally
Oxygen attracts electrons more strongly due to more protons, causing orbits closer to oxygen atom
It is polar - charge difference (oxygen slightly negative and hydrogen slightly positive)
Define and explain dipolarity’s function in water
Containing both positive and negative charge
Allows water to form weak association with polar or ionic molecules
Known as hydrogen bonding
What are the three properties of water
Thermal Properties
Cohesive / adhesive properties
Solvent properties
Explain Thermal properties of water
Hydrogen bonds have to be broken in order for water to change states
and to break these hydrogen bonds, energy has to be absorbed first
Comparison between water and methane
Similarities :
- Comparable size and weight (h2o = 18 and CH4 = 16)
- comparable valances both have a tetrahedral molecular geometry
Differences
- Water is polar, can form intermolecular hydrogen bonds
- Methane is non-polar, can only form weak dispersion forces between molecules
Comparison of thermal properties of water and methane
Water has a higher melting and boiling points
Water has a specific heat capacity
Water has higher heat of vaporization
Water as a higher heat of fusion
Explain why water is a good coolant
Water is evaporated on skin as sweat which cools us down
When water changes state from liquid to vapour it needs energy
When a human does sports or exercise
they generate heat
this heat causes water / sweat to evaporate to cool down skin
making it a highly effective coolant
Explain cohesive properties of water
Cohesion is the ability of like molecules to stick together
Water is strongly cohesive (it will form hydrogen bonds)
Explain adhesive properties of water
ability of dissimilar molecules to stick together
Water will form intermolecular associations with polar and charged molecules
Why is cohesive property important
The cohesive properties of water explain its surface tension
H bonding between water molecules allows the liquid to resist low levels of external force (surface tension)
The high surface tension of water makes it sufficiently dense for certain smaller organisms to move along its surface
Why is adhesive property important
The adhesive properties of water explain its capillary action
Attraction to charged or polar surfaces (e.g. glass) allows water to flow in opposition of gravitational forces (capillary action)
This capillary action is necessary to allow water to be transported up plant stems via a transpiration stream
Explain solvent properties of water
Water is known as universal solvent
can dissolve any substance that contains charged particles (ions) or electronegative atoms (polarity)
because the polar attraction of large quantities of water molecules can weaken intramolecular forces which dissociates atoms
The slightly charged regions of the water molecule surround atoms of opposing charge, forming dispersive hydration shells
why can substances can be hydrophilic or hydrophobic
Hydrophilic substances include all polar molecules and ions - can readily dissolve in water
Hydrophobic substances include large, non-polar molecules (such as fats and oils) - do not dissolve in water
Water soluble substances
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 – most oxygen is transported by haemoglobin within red blood cells
Glucose contains many hydroxyl groups (–OH) which may associate with water and thus can freely travel within the blood
Amino acids will be transported in the blood in an ionized state (either the amine and/or carboxyl groups may be charged)
