water Flashcards
geometry of water
tetrahedral
the ideal angle of tetrahedral is ___ degrees, but repulsion of e- from H pushes H together to ___ degrees
109.5; 104.5
each water molecule can form H bonds with ___ other water cules to form an inter-molecular network
4
H-bonds hold water molecules ___% closer together than without H-bonds
15
the anomalous properties of H2O are due to its _____ H-bonds
intra-molecular
why are H2O MP and BP so unusually high?
because of the H bonds
why does top freeze and bottom remain liquid?
because the bottom is 4 degrees, which is heaviest, so it stays at the bottom; meanwhile ice volume is larger, it floats on top
what is phase transition?
the transformation of a thermodynamic system from one phase to another
what are the 5 different phases of water?
liquid, vapour, solid, glass, supercritical fluid
food with aw > ___ and pH > ___ are regarded as potentially hazardous
0.85; 4.6
what are humactants?
salts, sugars, glycerol that prevent moisture migration from high water activity bread to the fillings
army rations are baked at ____ F
185
what is the latent heat of vapourization of water?
540 cal/g
what is the latent heat of fusion of ice?
80 cal/g
what do the colligative properties of water solely depend on?
the number of solute molecules dissolved
dissolving of solute ___ vapour pressure, ___ freezing point, ____ boiling point
lowers; lowers; raises
how is water activity calculated?
aw=vapour pressure of food (p)/vapour pressure of pure water (po)
what are the three states of water in food?
bound, capillary, free
these graphs of data show relation between aw and moisture content:
moisture sorption isotherm
