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Flashcards in water Deck (19):
1

geometry of water

tetrahedral

2

the ideal angle of tetrahedral is ___ degrees, but repulsion of e- from H pushes H together to ___ degrees

109.5; 104.5

3

each water molecule can form H bonds with ___ other water cules to form an inter-molecular network

4

4

H-bonds hold water molecules ___% closer together than without H-bonds

15

5

the anomalous properties of H2O are due to its _____ H-bonds

intra-molecular

6

why are H2O MP and BP so unusually high?

because of the H bonds

7

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

8

what is phase transition?

the transformation of a thermodynamic system from one phase to another

9

what are the 5 different phases of water?

liquid, vapour, solid, glass, supercritical fluid

10

food with aw > ___ and pH > ___ are regarded as potentially hazardous

0.85; 4.6

11

what are humactants?

salts, sugars, glycerol that prevent moisture migration from high water activity bread to the fillings

12

army rations are baked at ____ F

185

13

what is the latent heat of vapourization of water?

540 cal/g

14

what is the latent heat of fusion of ice?

80 cal/g

15

what do the colligative properties of water solely depend on?

the number of solute molecules dissolved

16

dissolving of solute ___ vapour pressure, ___ freezing point, ____ boiling point

lowers; lowers; raises

17

how is water activity calculated?

aw=vapour pressure of food (p)/vapour pressure of pure water (po)

18

what are the three states of water in food?

bound, capillary, free

19

these graphs of data show relation between aw and moisture content:

moisture sorption isotherm