Water
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Water is crucial to __________ of ______ and is present in all ____A___ systems - 3 common roles for water in ____A___ systems
• existence of life • food systems 1. carrier of nutrients and waste 2. reactant and reaction medium 3. stabilizer of biopolymer configuration (proteins and carbohydrates)
water’s (3) in food products is extremely important from standpoint of _________ and ________
1) amount of water 2) location of water 3) interaction of water with chemical components - acceptability and stability
texture is often associated with _________ (ie freeze-dried orange vs fresh orange)
moisture
because water is a major reactant and serves as a reaction ________, many of our food _________ and _________ methods involve the control of _________ content to slow down _________ reactions
• medium • preservation and processing methods • water • slow down deteriorative reactions
what (3) reduce water activity of a system?
• freezing • concentration • dehydration
what is one of the most abundant molecules on earth? - also the only common _________ and most abundant _________
water - only common liquid - most abundant solid
water is the only compound that exists in all _________ _________ under which conditions?
• all 3 states (solid, liquid and gas) • under conditions found on this planet
difference between water (____A_____ of oxygen) to other ____A_____ of other atoms (CH4, NH3, HF, H2S, H2Se, HeTe)?
• hydrate of oxygen • all other hydrates are gaseous at ambient temperature
relative to other hydrates, water is unusual in all of its physical properties (7)
• melting point • boiling point • surface tension • dielectric constant • heat of fusion • heat of vaporization • heat of sublimation
Oxygen has ___ electrons, ___ of which are valence electrons + 2 H have ___ electrons each - the 3 ____ orbitals and the ___ orbitals of oxygen atom are combined to form 4 ____ hybrid orbitals - only 2 of oxygen’s ___ valence electrons are used up in the # covalent bonds that form between H and O - the net result is that there are 2 oxygen _______ ________ _____ left in 2 of the _____ orbitals
• 8 e- –> 6 are valence + 2 hydrogen have 1 electrons each • three 2p orbitals and one 2s orbital –> 4 sp3 hybrid orbitals • 2 of 6 valence e- used in the 2 covalent bonds • 2 O lone electron pairs left in 2 of the sp3 orbitals
because of its lone electron pairs, O is highly _________ –> hence covalent bond formed with hydrogen is uniform/not uniform and the electron from Hydrogen is drawn away/towards Oxygen - the result is a(n) increase/lowering of the electron _________ around the hydrogen atom –> giving it a slight negative/positive character (electron-rich/poor) - the 2 lone e^pairs of O produce 2 regions of _________ character (electron rich/poor) relative to the _________
• electronegative –> bond is not uniform • H electrons drawn towards O • lowering of electron shield –> positive character (e- poor) • negative character (e- rich) relative to hydrogens
water molecules can be viewed as having # electron rich regions and # electron poor regions situated _________ally - in the presence of other water molecules, these regions of differential electron density will lead to _________ to minimize overall _________ _________ of system
2 rich + 2 poor - tetrahedrally - association –> overall energy
what spacial arrangements of e- rich and e- poor regions of water promotes ability to form 3D associations or networks?
tetrahedral nature
although hydrogen bonds are not very _________ (# kcal/mol) –> _________ can be formed = _________ effect - hydrogen bonding is the basis for water _________ _________ in atmosphere, leading to formation of _________
• strong (10 kcal/mol) • many can be formed –> cumulative effect • water vapor accumulation –> formation of clouds
what is the transitional structure of water called in its liquid phase? - regions of 3D _______-_______ water molecules somewhat similar in structure to _____
• flickering clusters • hydrogen-bonded • similar to ice
lifetime of flickering clusters?
10^-10 to 10^-11 seconds - continually form and break up
increase in temperature = - increase/decrease of number of clusters - increase/decrease of number of molecules per cluster
• increase in number of clusters • decrease in number of molecules per cluster
flickering cluster - exist at boiling point of water? - special feature of their structure? - have been postulated to explain the relatively normal (low) _________ of water
• yes • hole in the middle • normal viscosity of water
when ionic compounds dissolved in water, they ________ into their respective _______ - due to the _______ nature of water –> this _______ is sufficient/insufficient to break _______ bonds, but can dissociate _______ bonds by allowing multiple water molecules to act as _______ for opposing charged ionic species - hence, when NaCl is dissolved, each ion is _______ by water which substitutes its polar contributions for the _______ charges of the respective _______
• ionize into their respective ions • very polar nature of water molecule –> polarity is insufficient to break covalent bonds but can dissociate ionic bonds • act a counterions • each ion is hydrated by water • for the opposing charges of the respective ion
what forms around each ion to neutralize the charge of the respective ion? - this forces water into a _______ orientation around each ion, therefore disrupting the normal structure of water
• hydration shell • specific orientation
The formation of bulky hydrates generally causes an increase/decrease in viscosity and tends to increase/decrease the freezing point of a system
• increase in viscosity • decrease in freezing point of system
water around a hydrogen bonding site on a molecule will associate in a manner that disrupts the natural _______ geometry of water - overall effect is to _______ up water locally in a similar manner as occurs with _______ compounds - hydrogen bonding solutes will disrupt water structure –> number of flickering clusters will increase/decrease
tetrahedral geometry - tie up water - ionic compounds - number of flickering clusters will decrease
what happens with water in presence of macromolecules that have a large number of hydrogen bonding sites (polypeptides, proteins, carbohydrates, and polysacs)?
the water can be completely or extensively immobilized by hydrogen bonding if amount of water present is limited
when low concentrations of nonpolar substances (hydrocarbons, FA, nonpolar side chains of proteins) are dissolved or dispersed in water, _____-_______ _______ are though to be induced - explain
ice-like inclusions - formation of ice-like structure around a nonpolar group or molecule has been postulated to minimize the free energy state of system when symmetric electron-neutral constituents and asymmetric electron-rich hydrophilic materials are forced to associate