Structure and properties of water
- thermal properties of water
- water freezes and boils at higher temperatures than other
similar
compounds
(Fig)
- water is a polar molecule (Fig)
- concept of hydrogen bonds (Fig)
- heat capacity
- experiment: heating water in a paper
tray.
Why is
the paper not burning?
- About 1 calorie (the basic unit) of heat is needed to raise the
temperature
of 1g of water by 1oC. Specific heat capacity of water is
larger
than for most substances.
- phase changes of water as a function of added heat (Fig)
- latent heat of vaporization (539 cal/g) and fusion (80 cal/g);
1
calorie
(cal) = 4.184 joule (J)
- teh NY Times had an article in January 2007 about how farmers
protected their citrus fruit crop by irrigating with water (Fig)
- density of water
- density of water as a function of temperature. Water has its
highest
density
at 4oC. Water volume increases by 9% when it changes from
water
to ice (Fig)
- definition of density: mass per volume
- explanation based on hydrogen bond model (Fig)(Fig)(Fig)(Fig)
- viscosity
- viscosity of water decreases by 3% per oC increase
in
temperature
(Fig A2.1)
- experiment: measuring the flow
velocity of cold and
hot water in a capillary
- surface tension
- capillarity: in a 1/8 mm diameter tube water would rise more
than 25cm
(Fig)
- h = 2*sigma /
(r*rho*g); sigma: specific surface tension, rho: density, g: gravity
constant, r: radius of capillary
- sigma (at 18oC) = 0.0729 N/m
- experiment:
suspended paper clip and influence of
dishwashing liquid (Fig)
- experiment: measure rise
of water in a capillary (ID = 1mm) (Fig)
- adhesion/cohesion
- Absoption of radiation
- large in infrared and ultraviolet regions, less in visible
regions (Fig)
- compressibility
- compressibility of water is small. An increase of pressure by 1
atmosphere
(= 1013mbar = 14.7 psi) causes a decrease of the water volume by 5.3*10-5
of the original volume.
- solubility
- water is able to dissolve huge quantities of salts and is
therefore an
important factor in transporting substances in nature
- more than 300g of NaCl can be dissolved in a kg of water
- hydrophobic, hydrophilic substances, soap has hydrophobic &
hydrophilic ends, e.g. CH3(CH2)16CO2-Na+
- summary
Resources:
- Manning, J.C. (1997), chapter 2; see books on reserve.
- Hornberger et al. (1998), Appendix 3.
- equipment used for
experiments
